数据库SQL优化大总结1之- 百万级数据库优化方案

╰+攻爆jí腚メ 2022-05-20 02:19 154阅读 0赞

转自：[https://mp.weixin.qq.com/s?\_\_biz=MzIxMjg4NDU1NA==&mid=2247483684&idx=1&sn=f5abc60e696b2063e43cd9ccb40df101&chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&mpshare=1&scene=1&srcid=0606XGHeBS4RBZloVv786wBY\#rd][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[一、百万级数据库优化方案][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[1.对查询进行优化，要尽量避免全表扫描，首先应考虑在 where 及 order by 涉及的列上建立索引。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2.应尽量避免在 where 子句中对字段进行 null 值判断，否则将导致引擎放弃使用索引而进行全表扫描，如：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select id from t where num is null

[最好不要给数据库留NULL，尽可能的使用 NOT NULL填充数据库.][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[备注、描述、评论之类的可以设置为 NULL，其他的，最好不要使用NULL。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[不要以为 NULL 不需要空间，比如：char(100) 型，在字段建立时，空间就固定了， 不管是否插入值（NULL也包含在内），都是占用 100个字符的空间的，如果是varchar这样的变长字段， null 不占用空间。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[  
可以在num上设置默认值0，确保表中num列没有null值，然后这样查询：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select id from t where num = 0

[  
][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3.应尽量避免在 where 子句中使用 != 或 <> 操作符，否则将引擎放弃使用索引而进行全表扫描。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[4.应尽量避免在 where 子句中使用 or 来连接条件，如果一个字段有索引，一个字段没有索引，将导致引擎放弃使用索引而进行全表扫描，如：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select id from t where num=10 or Name = 'admin'

[可以这样查询：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select id from t where num = 10 union allselect id from t where Name = 'admin'

[  
5.in和 not in 也要慎用，否则会导致全表扫描，如：  
][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select id from t where num in(1,2,3)

[对于连续的数值，能用 between就不要用 in 了：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select id from t where num between 1 and 3

[很多时候用 exists 代替 in 是一个好的选择：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select num from a where num in(select num from b)

[用下面的语句替换：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select num from a where exists(select 1 from b where num=a.num)

[6.下面的查询也将导致全表扫描：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select id from t where name like ‘%abc%’

[若要提高效率，可以考虑全文检索。  
  
7.如果在 where 子句中使用参数，也会导致全表扫描。因为SQL只有在运行时才会解析局部变量，但优化程序不能将访问计划的选择推迟到运行时；它必须在编译时进行选择。然 而，如果在编译时建立访问计划，变量的值还是未知的，因而无法作为索引选择的输入项。如下面语句将进行全表扫描：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select id from t where num = @num

[可以改为强制查询使用索引：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select id from t with(index(索引名)) where num = @num

[应尽量避免在 where子句中对字段进行表达式操作，这将导致引擎放弃使用索引而进行全表扫描。如：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select id from t where num/2 = 100

[应改为:][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select id from t wherenum = 100*2

[  
9.应尽量避免在where子句中对字段进行函数操作，这将导致引擎放弃使用索引而进行全表扫描。如：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1.  [select id from t where substring(name,1,3) = ’abc’ -–name以abc开头的id][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2.  [select id from t where datediff(day,createdate,’2005\-11\-30′) = 0 \-–‘2005\-11\-30’ *--生成的id*][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1. [select id from t where name like 'abc%'][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2. [select id from t where createdate >= '2005-11-30' and createdate < '2005-12-1'][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[  
10.不要在 where 子句中的“=”左边进行函数、算术运算或其他表达式运算，否则系统将可能无法正确使用索引。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[11.在使用索引字段作为条件时，如果该索引是复合索引，那么必须使用到该索引中的第一个字段作为条件时才能保证系统使用该索引，否则该索引将不会被使用，并且应尽可能的让字段顺序与索引顺序相一致。  
  
12.不要写一些没有意义的查询，如需要生成一个空表结构：  
][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select col1,col2 into #t from t where 1=0

[这类代码不会返回任何结果集，但是会消耗系统资源的，应改成这样：  
][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

create table #t(…)

[13.Update 语句，如果只更改1、2个字段，不要Update全部字段，否则频繁调用会引起明显的性能消耗，同时带来大量日志。  
  
14.对于多张大数据量（这里几百条就算大了）的表JOIN，要先分页再JOIN，否则逻辑读会很高，性能很差。  
  
15.select count(\*) from table；这样不带任何条件的count会引起全表扫描，并且没有任何业务意义，是一定要杜绝的。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[  
16.索引并不是越多越好，索引固然可以提高相应的 select 的效率，但同时也降低了 insert 及 update 的效率，因为 insert 或 update 时有可能会重建索引，所以怎样建索引需要慎重考虑，视具体情况而定。一个表的索引数最好不要超过6个，若太多则应考虑一些不常使用到的列上建的索引是否有 必要。  
  
17.应尽可能的避免更新 clustered 索引数据列，因为 clustered 索引数据列的顺序就是表记录的物理存储顺序，一旦该列值改变将导致整个表记录的顺序的调整，会耗费相当大的资源。若应用系统需要频繁更新 clustered 索引数据列，那么需要考虑是否应将该索引建为 clustered 索引。  
  
18.尽量使用数字型字段，若只含数值信息的字段尽量不要设计为字符型，这会降低查询和连接的性能，并会增加存储开销。这是因为引擎在处理查询和连 接时会逐个比较字符串中每一个字符，而对于数字型而言只需要比较一次就够了。  
  
19.尽可能的使用 varchar/nvarchar代替 char/nchar ，因为首先变长字段存储空间小，可以节省存储空间，其次对于查询来说，在一个相对较小的字段内搜索效率显然要高些。  
  
20.任何地方都不要使用 select \* from t ，用具体的字段列表代替“\*”，不要返回用不到的任何字段。  
  
21.尽量使用表变量来代替临时表。如果表变量包含大量数据，请注意索引非常有限（只有主键索引）。  
  
22. 避免频繁创建和删除临时表，以减少系统表资源的消耗。临时表并不是不可使用，适当地使用它们可以使某些例程更有效，例如，当需要重复引用大型表或常用表中的某个数据集时。但是，对于一次性事件， 最好使用导出表。  
  
23.在新建临时表时，如果一次性插入数据量很大，那么可以使用 select into 代替 create table，避免造成大量 log ，以提高速度；如果数据量不大，为了缓和系统表的资源，应先create table，然后insert。  
  
24.如果使用到了临时表，在存储过程的最后务必将所有的临时表显式删除，先 truncate table ，然后 drop table ，这样可以避免系统表的较长时间锁定。  
  
25.尽量避免使用游标，因为游标的效率较差，如果游标操作的数据超过1万行，那么就应该考虑改写。  
  
26.使用基于游标的方法或临时表方法之前，应先寻找基于集的解决方案来解决问题，基于集的方法通常更有效。  
  
27.与临时表一样，游标并不是不可使用。对小型数据集使用 FAST\_FORWARD 游标通常要优于其他逐行处理方法，尤其是在必须引用几个表才能获得所需的数据时。在结果集中包括“合计”的例程通常要比使用游标执行的速度快。如果开发时 间允许，基于游标的方法和基于集的方法都可以尝试一下，看哪一种方法的效果更好。  
  
28.在所有的存储过程和触发器的开始处设置 SET NOCOUNT ON ，在结束时设置 SET NOCOUNT OFF 。无需在执行存储过程和触发器的每个语句后向客户端发送 DONE\_IN\_PROC 消息。  
  
29.尽量避免大事务操作，提高系统并发能力。  
  
30.尽量避免向客户端返回大数据量，若数据量过大，应该考虑相应需求是否合理。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[实际案例分析：拆分大的 DELETE 或INSERT 语句，批量提交SQL语句  
　　如果你需要在一个在线的网站上去执行一个大的 DELETE 或 INSERT 查询，你需要非常小心，要避免你的操作让你的整个网站停止相应。因为这两个操作是会锁表的，表一锁住了，别的操作都进不来了。  
　　Apache 会有很多的子进程或线程。所以，其工作起来相当有效率，而我们的服务器也不希望有太多的子进程，线程和数据库链接，这是极大的占服务器资源的事情，尤其是内存。  
　　如果你把你的表锁上一段时间，比如30秒钟，那么对于一个有很高访问量的站点来说，这30秒所积累的访问进程/线程，数据库链接，打开的文件数，可能不仅仅会让你的WEB服务崩溃，还可能会让你的整台服务器马上挂了。  
　　所以，如果你有一个大的处理，你一定把其拆分，使用 LIMIT Oracle(rownum),sqlserver(top)条件是一个好的方法。下面是一个MySQL示例：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1. [while(1)\{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3. [ 　　//每次只做1000条　　 mysql\_query(“delete from logs where log\_date <= ’2012\-11\-01’ limit 1000”);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
4. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
5. [ 　　if(mysql\_affected\_rows() == 0)\{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
6. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
7. [　　 　　//删除完成，退出！　　 　　break；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
8. [　　\}//每次暂停一段时间，释放表让其他进程/线程访问。usleep(50000)][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
9. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
10. [\}][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[二、数据库访问性能优化][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[特别说明：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[1、  本文只是面对数据库应用开发的程序员，不适合专业DBA，DBA在数据库性能优化方面需要了解更多的知识；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2、  本文许多示例及概念是基于Oracle数据库描述，对于其它关系型数据库也可以参考，但许多观点不适合于KV数据库或内存数据库或者是基于SSD技术的数据库；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3、  本文未深入数据库优化中最核心的执行计划分析技术。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[读者对像：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[开发人员：如果你是做数据库开发，那本文的内容非常适合，因为本文是从程序员的角度来谈数据库性能优化。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[架构师：如果你已经是数据库应用的架构师，那本文的知识你应该清楚90%，否则你可能是一个喜欢折腾的架构师。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[DBA（数据库管理员）：大型数据库优化的知识非常复杂，本文只是从程序员的角度来谈性能优化，DBA除了需要了解这些知识外，还需要深入数据库的内部体系架构来解决问题。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[    在网上有很多文章介绍数据库优化知识，但是大部份文章只是对某个一个方面进行说明，而对于我们程序员来说这种介绍并不能很好的掌握优化知识，因为很多介绍只是对一些特定的场景优化的，所以反而有时会产生误导或让程序员感觉不明白其中的奥妙而对数据库优化感觉很神秘。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[    很多程序员总是问如何学习数据库优化，有没有好的教材之类的问题。在书店也看到了许多数据库优化的专业书籍，但是感觉更多是面向DBA或者是PL/SQL开发方面的知识，个人感觉不太适合普通程序员。而要想做到数据库优化的高手，不是花几周，几个月就能达到的，这并不是因为数据库优化有多高深，而是因为要做好优化一方面需要有非常好的技术功底，对操作系统、存储硬件网络、数据库原理等方面有比较扎实的基础知识，另一方面是需要花大量时间对特定的数据库进行实践测试与总结。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[    作为一个程序员，我们也许不清楚线上正式的服务器硬件配置，我们不可能像DBA那样专业的对数据库进行各种实践测试与总结，但我们都应该非常了解我们SQL的业务逻辑，我们清楚SQL中访问表及字段的数据情况，我们其实只关心我们的SQL是否能尽快返回结果。那程序员如何利用已知的知识进行数据库优化？如何能快速定位SQL性能问题并找到正确的优化方向？][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[面对这些问题，笔者总结了一些面向程序员的基本优化法则，本文将结合实例来坦述数据库开发的优化知识。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[    要正确的优化SQL，我们需要快速定位能性的瓶颈点，也就是说快速找到我们SQL主要的开销在哪里？而大多数情况性能最慢的设备会是瓶颈点，如下载时网络速度可能会是瓶颈点，本地复制文件时硬盘可能会是瓶颈点，为什么这些一般的工作我们能快速确认瓶颈点呢，因为我们对这些慢速设备的性能数据有一些基本的认识，如网络带宽是2Mbps，硬盘是每分钟7200转等等。因此，为了快速找到SQL的性能瓶颈点，我们也需要了解我们计算机系统的硬件基本性能指标，下图展示的当前主流计算机性能指标数据。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[![640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1][]][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[从图上可以看到基本上每种设备都有两个指标：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[延时（响应时间）：表示硬件的突发处理能力；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[带宽（吞吐量）：代表硬件持续处理能力。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[从上图可以看出，计算机系统硬件性能从高到代依次为：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[CPU——Cache(L1-L2-L3)——内存——SSD硬盘——网络——硬盘][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[由于SSD硬盘还处于快速发展阶段，所以本文的内容不涉及SSD相关应用系统。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[根据数据库知识，我们可以列出每种硬件主要的工作内容：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[CPU及内存：缓存数据访问、比较、排序、事务检测、SQL解析、函数或逻辑运算；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[网络：结果数据传输、SQL请求、远程数据库访问（dblink）；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[硬盘：数据访问、数据写入、日志记录、大数据量排序、大表连接。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[根据当前计算机硬件的基本性能指标及其在数据库中主要操作内容，可以整理出如下图所示的性能基本优化法则：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[这个优化法则归纳为5个层次：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[1、  减少数据访问（减少磁盘访问）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2、  返回更少数据（减少网络传输或磁盘访问）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3、  减少交互次数（减少网络传输）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[4、  减少服务器CPU开销（减少CPU及内存开销）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[5、  利用更多资源（增加资源）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[由于每一层优化法则都是解决其对应硬件的性能问题，所以带来的性能提升比例也不一样。传统数据库系统设计是也是尽可能对低速设备提供优化方法，因此针对低速设备问题的可优化手段也更多，优化成本也更低。我们任何一个SQL的性能优化都应该按这个规则由上到下来诊断问题并提出解决方案，而不应该首先想到的是增加资源解决问题。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[以下是每个优化法则层级对应优化效果及成本经验参考：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[![0_wx_fmt_gif_wxfrom_5_wx_lazy_1][]][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[接下来，我们针对5种优化法则列举常用的优化手段并结合实例分析。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

# [二、oracle数据库两个基本概念][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd] #

[数据块是数据库中数据在磁盘中存储的最小单位，也是一次IO访问的最小单位，一个数据块通常可以存储多条记录，数据块大小是DBA在创建数据库或表空间时指定，可指定为2K、4K、8K、16K或32K字节。下图是一个Oracle数据库典型的物理结构，一个数据库可以包括多个数据文件，一个数据文件内又包含多个数据块；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[![640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 1][]][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ROWID是每条记录在数据库中的唯一标识，通过ROWID可以直接定位记录到对应的文件号及数据块位置。ROWID内容包括文件号、对像号、数据块号、记录槽号，如下图所示：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[![640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 2][]][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[三、数据库访问优化法则详解][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[减少数据访问][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[创建并使用正确的索引][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[数据库索引的原理非常简单，但在复杂的表中真正能正确使用索引的人很少，即使是专业的DBA也不一定能完全做到最优。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[索引会大大增加表记录的DML(INSERT,UPDATE,DELETE)开销，正确的索引可以让性能提升100，1000倍以上，不合理的索引也可能会让性能下降100倍，因此在一个表中创建什么样的索引需要平衡各种业务需求。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[索引常见问题：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[索引有哪些种类？][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[常见的索引有B-TREE索引、位图索引、全文索引，位图索引一般用于数据仓库应用，全文索引由于使用较少，这里不深入介绍。B-TREE索引包括很多扩展类型，如组合索引、反向索引、函数索引等等，以下是B-TREE索引的简单介绍：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[B-TREE索引也称为平衡树索引(Balance Tree)，它是一种按字段排好序的树形目录结构，主要用于提升查询性能和唯一约束支持。B-TREE索引的内容包括根节点、分支节点、叶子节点。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[叶子节点内容：索引字段内容+表记录ROWID][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[根节点，分支节点内容：当一个数据块中不能放下所有索引字段数据时，就会形成树形的根节点或分支节点，根节点与分支节点保存了索引树的顺序及各层级间的引用关系。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[         一个普通的BTREE索引结构示意图如下所示：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[![640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 3][]][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果我们把一个表的内容认为是一本字典，那索引就相当于字典的目录，如下图所示：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[![640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 4][]][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[![640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 5][]][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[图中是一个字典按部首+笔划数的目录，相当于给字典建了一个按部首+笔划的组合索引。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[一个表中可以建多个索引，就如一本字典可以建多个目录一样（按拼音、笔划、部首等等）。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[一个索引也可以由多个字段组成，称为组合索引，如上图就是一个按部首+笔划的组合目录。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[SQL什么条件会使用索引？][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[当字段上建有索引时，通常以下情况会使用索引：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1. [INDEX\_COLUMN = ?][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3. [INDEX\_COLUMN > ?][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
4. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
5. [INDEX\_COLUMN >= ?][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
6. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
7. [INDEX\_COLUMN < ?][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
8. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
9. [INDEX\_COLUMN <= ?][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
10. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
11. [INDEX\_COLUMN between ? and ?][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
12. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
13. [INDEX\_COLUMN in (?,?,...,?)][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
14. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
15. [INDEX\_COLUMN like ?||'%'（后导模糊查询）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
16. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
17. [T1. INDEX\_COLUMN=T2. COLUMN1（两个表通过索引字段关联）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[SQL什么条件不会使用索引？  
][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

<table style="border-spacing:0px;color:rgb(51,51,51);font-family:'-apple-system', 'SF UI Text', Arial, 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'WenQuanYi Micro Hei', sans-serif, SimHei, SimSun;font-size:14px;background-color:rgb(255,255,255);"> 
 <tbody> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">查询条件</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">不能使用索引原因</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">INDEX_COLUMN &lt;&gt; ?</a><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">INDEX_COLUMN not in (?,?,...,?)</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">不等于操作不能使用索引</a></td> 
 </tr> 
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 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">function(INDEX_COLUMN) = ?</a><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">INDEX_COLUMN + 1 = ?</a><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">INDEX_COLUMN || 'a' = ?</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">经过普通运算或函数运算后的索引字段不能使用索引</a></td> 
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 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">INDEX_COLUMN like '%'||?</a><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">INDEX_COLUMN like '%'||?||'%'</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">含前导模糊查询的Like语法不能使用索引</a></td> 
 </tr> 
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 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">INDEX_COLUMN is null</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">B-TREE索引里不保存字段为NULL值记录，因此IS NULL不能使用索引</a></td> 
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 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">NUMBER_INDEX_COLUMN='12345'</a><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">CHAR_INDEX_COLUMN=12345</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">Oracle在做数值比较时需要将两边的数据转换成同一种数据类型，如果两边数据类型不同时会对字段值隐式转换，相当于加了一层函数处理，所以不能使用索引。</a></td> 
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 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">a.INDEX_COLUMN=a.COLUMN_1</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">给索引查询的值应是已知数据，不能是未知字段值。</a></td> 
 </tr> 
 <tr> 
 <td colspan="2"><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">注：</a><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">经过函数运算字段的字段要使用可以使用函数索引，这种需求建议与DBA沟通。</a><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">有时候我们会使用多个字段的组合索引，如果查询条件中第一个字段不能使用索引，那整个查询也不能使用索引</a><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">如：我们company表建了一个id+name的组合索引，以下SQL是不能使用索引的</a><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">Select * from company where name=?</a><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">Oracle9i后引入了一种index skip scan的索引方式来解决类似的问题，但是通过index skip scan提高性能的条件比较特殊，使用不好反而性能会更差。</a><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">&nbsp;</a></td> 
 </tr> 
 </tbody> 
</table>

[我们一般在什么字段上建索引？][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[这是一个非常复杂的话题，需要对业务及数据充分分析后再能得出结果。主键及外键通常都要有索引，其它需要建索引的字段应满足以下条件：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[1、字段出现在查询条件中，并且查询条件可以使用索引；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2、语句执行频率高，一天会有几千次以上；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3、通过字段条件可筛选的记录集很小，那数据筛选比例是多少才适合？][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[这个没有固定值，需要根据表数据量来评估，以下是经验公式，可用于快速评估：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[小表(记录数小于10000行的表)：筛选比例<10%；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[大表：(筛选返回记录数)<(表总记录数\*单条记录长度)/10000/16][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[      单条记录长度≈字段平均内容长度之和+字段数\*2][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[以下是一些字段是否需要建B-TREE索引的经验分类：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

<table style="border-spacing:0px;color:rgb(51,51,51);font-family:'-apple-system', 'SF UI Text', Arial, 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'WenQuanYi Micro Hei', sans-serif, SimHei, SimSun;font-size:14px;background-color:rgb(255,255,255);"> 
 <tbody> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow"> </a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">字段类型</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">常见字段名</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">需要建索引的字段</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">主键</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">ID,PK</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">外键</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">PRODUCT_ID,COMPANY_ID,MEMBER_ID,ORDER_ID,TRADE_ID,PAY_ID</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">有对像或身份标识意义字段</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">HASH_CODE,USERNAME,IDCARD_NO,EMAIL,TEL_NO,IM_NO</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">索引慎用字段,需要进行数据分布及使用场景详细评估</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">日期</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">GMT_CREATE,GMT_MODIFIED</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">年月</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">YEAR,MONTH</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">状态标志</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">PRODUCT_STATUS,ORDER_STATUS,IS_DELETE,VIP_FLAG</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">类型</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">ORDER_TYPE,IMAGE_TYPE,GENDER,CURRENCY_TYPE</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">区域</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">COUNTRY,PROVINCE,CITY</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">操作人员</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">CREATOR,AUDITOR</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">数值</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">LEVEL,AMOUNT,SCORE</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">长字符</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">ADDRESS,COMPANY_NAME,SUMMARY,SUBJECT</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">不适合建索引的字段</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">描述备注</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">DESCRIPTION,REMARK,MEMO,DETAIL</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">大字段</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">FILE_CONTENT,EMAIL_CONTENT</a></td> 
 </tr> 
 </tbody> 
</table>

[如何知道SQL是否使用了正确的索引？][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[简单SQL可以根据索引使用语法规则判断，复杂的SQL不好办，判断SQL的响应时间是一种策略，但是这会受到数据量、主机负载及缓存等因素的影响，有时数据全在缓存里，可能全表访问的时间比索引访问时间还少。要准确知道索引是否正确使用，需要到数据库中查看SQL真实的执行计划，这个话题比较复杂，详见SQL执行计划专题介绍。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[索引对DML(INSERT,UPDATE,DELETE)附加的开销有多少？][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[这个没有固定的比例，与每个表记录的大小及索引字段大小密切相关，以下是一个普通表测试数据，仅供参考：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[索引对于Insert性能降低56%][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[索引对于Update性能降低47%][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[索引对于Delete性能降低29%][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[因此对于写IO压力比较大的系统，表的索引需要仔细评估必要性，另外索引也会占用一定的存储空间。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[1.2、只通过索引访问数据][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[有些时候，我们只是访问表中的几个字段，并且字段内容较少，我们可以为这几个字段单独建立一个组合索引，这样就可以直接只通过访问索引就能得到数据，一般索引占用的磁盘空间比表小很多，所以这种方式可以大大减少磁盘IO开销。如：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select id,name from company where type='2';

[如果这个SQL经常使用，我们可以在type,id,name上创建组合索引][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

create index my_comb_index on company(type,id,name);

[有了这个组合索引后，SQL就可以直接通过my\_comb\_index索引返回数据，不需要访问company表。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[还是拿字典举例：有一个需求，需要查询一本汉语字典中所有汉字的个数，如果我们的字典没有目录索引，那我们只能从字典内容里一个一个字计数，最后返回结果。如果我们有一个拼音目录，那就可以只访问拼音目录的汉字进行计数。如果一本字典有1000页，拼音目录有20页，那我们的数据访问成本相当于全表访问的50分之一。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[切记，性能优化是无止境的，当性能可以满足需求时即可，不要过度优化。在实际数据库中我们不可能把每个SQL请求的字段都建在索引里，所以这种只通过索引访问数据的方法一般只用于核心应用，也就是那种对核心表访问量最高且查询字段数据量很少的查询。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[1.3、优化SQL执行计划][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[SQL执行计划是关系型数据库最核心的技术之一，它表示SQL执行时的数据访问算法。由于业务需求越来越复杂，表数据量也越来越大，程序员越来越懒惰，SQL也需要支持非常复杂的业务逻辑，但SQL的性能还需要提高，因此，优秀的关系型数据库除了需要支持复杂的SQL语法及更多函数外，还需要有一套优秀的算法库来提高SQL性能。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[目前ORACLE有SQL执行计划的算法约300种，而且一直在增加，所以SQL执行计划是一个非常复杂的课题，一个普通DBA能掌握50种就很不错了，就算是资深DBA也不可能把每个执行计划的算法描述清楚。虽然有这么多种算法，但并不表示我们无法优化执行计划，因为我们常用的SQL执行计划算法也就十几个，如果一个程序员能把这十几个算法搞清楚，那就掌握了80%的SQL执行计划调优知识。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[由于篇幅的原因，SQL执行计划需要专题介绍，在这里就不多说了。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2、返回更少的数据][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2.1、数据分页处理][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[一般数据分页方式有：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2.1.1、客户端(应用程序或浏览器)分页][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[将数据从应用服务器全部下载到本地应用程序或浏览器，在应用程序或浏览器内部通过本地代码进行分页处理][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[优点：编码简单，减少客户端与应用服务器网络交互次数][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[缺点：首次交互时间长，占用客户端内存][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[适应场景：客户端与应用服务器网络延时较大，但要求后续操作流畅，如手机GPRS，超远程访问（跨国）等等。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2.1.2、应用服务器分页][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[将数据从数据库服务器全部下载到应用服务器，在应用服务器内部再进行数据筛选。以下是一个应用服务器端Java程序分页的示例：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1.  [List list=executeQuery(“select \* from employee order by id”);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2.  [Int count= list.size();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3.  [List subList= list.subList(10, 20);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[优点：编码简单，只需要一次SQL交互，总数据与分页数据差不多时性能较好。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[缺点：总数据量较多时性能较差。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[适应场景：数据库系统不支持分页处理，数据量较小并且可控。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2.1.3、数据库SQL分页][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[采用数据库SQL分页需要两次SQL完成][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[一个SQL计算总数量][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[一个SQL返回分页后的数据][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[优点：性能好][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[缺点：编码复杂，各种数据库语法不同，需要两次SQL交互。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[oracle数据库一般采用rownum来进行分页，常用分页语法有如下两种：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[直接通过rownum分页：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1. [select \* from (][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2. [ select a.\*,rownum rn from][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3. [ (select \* from product a where company\_id=? order by status) a][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
4. [ where rownum<=20)][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
5. [where rn>10;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[数据访问开销=索引IO+索引全部记录结果对应的表数据IO][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[采用rowid分页语法][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[优化原理是通过纯索引找出分页记录的ROWID，再通过ROWID回表返回数据，要求内层查询和排序字段全在索引里。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1. [create index myindex on product(company\_id,status);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2. [select b.\* from (][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3. [ select \* from (][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
4. [ select a.\*,rownum rn from][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
5. [ (select rowid rid,status from product a where company\_id=? order by status) a][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
6. [ where rownum<=20)][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
7. [ where rn>10) a, product b][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
8. [where a.rid=b.rowid;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[数据访问开销=索引IO+索引分页结果对应的表数据IO][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[实例：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[一个公司产品有1000条记录，要分页取其中20个产品，假设访问公司索引需要50个IO，2条记录需要1个表数据IO。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[那么按第一种ROWNUM分页写法，需要550(50+1000/2)个IO，按第二种ROWID分页写法，只需要60个IO(50+20/2);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2.2、只返回需要的字段][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[通过去除不必要的返回字段可以提高性能，例：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1.  [调整前：select \* from product where company\_id=?;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2.  [调整后：select id,name from product where company\_id=?;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[优点：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[1、减少数据在网络上传输开销][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2、减少服务器数据处理开销][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3、减少客户端内存占用][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[4、字段变更时提前发现问题，减少程序BUG][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[5、如果访问的所有字段刚好在一个索引里面，则可以使用纯索引访问提高性能。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[缺点：增加编码工作量][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[由于会增加一些编码工作量，所以一般需求通过开发规范来要求程序员这么做，否则等项目上线后再整改工作量更大。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果你的查询表中有大字段或内容较多的字段，如备注信息、文件内容等等，那在查询表时一定要注意这方面的问题，否则可能会带来严重的性能问题。如果表经常要查询并且请求大内容字段的概率很低，我们可以采用分表处理，将一个大表分拆成两个一对一的关系表，将不常用的大内容字段放在一张单独的表中。如一张存储上传文件的表：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

T_FILE（ID,FILE_NAME,FILE_SIZE,FILE_TYPE,FILE_CONTENT）

[我们可以分拆成两张一对一的关系表：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1.  [T\_FILE（ID,FILE\_NAME,FILE\_SIZE,FILE\_TYPE）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2.  [T\_FILECONTENT（ID, FILE\_CONTENT）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[  通过这种分拆，可以大大提少T\_FILE表的单条记录及总大小，这样在查询T\_FILE时性能会更好，当需要查询FILE\_CONTENT字段内容时再访问T\_FILECONTENT表。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3、减少交互次数][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3.1、batch DML][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[数据库访问框架一般都提供了批量提交的接口，jdbc支持batch的提交处理方法，当你一次性要往一个表中插入1000万条数据时，如果采用普通的executeUpdate处理，那么和服务器交互次数为1000万次，按每秒钟可以向数据库服务器提交10000次估算，要完成所有工作需要1000秒。如果采用批量提交模式，1000条提交一次，那么和服务器交互次数为1万次，交互次数大大减少。采用batch操作一般不会减少很多数据库服务器的物理IO，但是会大大减少客户端与服务端的交互次数，从而减少了多次发起的网络延时开销，同时也会降低数据库的CPU开销。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[假设要向一个普通表插入1000万数据，每条记录大小为1K字节，表上没有任何索引，客户端与数据库服务器网络是100Mbps，以下是根据现在一般计算机能力估算的各种batch大小性能对比值：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

<table style="border-spacing:0px;color:rgb(51,51,51);font-family:'-apple-system', 'SF UI Text', Arial, 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'WenQuanYi Micro Hei', sans-serif, SimHei, SimSun;font-size:14px;background-color:rgb(255,255,255);"> 
 <tbody> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">　单位：ms</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">No batch</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">Batch=10</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">Batch=100</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">Batch=1000</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">Batch=10000</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">服务器事务处理时间</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.1</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.1</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.1</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.1</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.1</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">服务器IO处理时间</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.02</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.2</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">2</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">20</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">200</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">网络交互发起时间</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.1</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.1</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.1</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.1</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.1</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">网络数据传输时间</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.01</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.1</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">1</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">10</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">100</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">小计</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.23</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.5</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">3.2</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">30.2</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">300.2</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">平均每条记录处理时间</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.23</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.05</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.032</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.0302</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">0.03002</a></td> 
 </tr> 
 </tbody> 
</table>

[从上可以看出，Insert操作加大Batch可以对性能提高近8倍性能，一般根据主键的Update或Delete操作也可能提高2-3倍性能，但不如Insert明显，因为Update及Delete操作可能有比较大的开销在物理IO访问。以上仅是理论计算值，实际情况需要根据具体环境测量。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3.2、In List][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[很多时候我们需要按一些ID查询数据库记录，我们可以采用一个ID一个请求发给数据库，如下所示：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1.  [for :var in ids\[\] do begin][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2.  [ select \* from mytable where id=:var;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3.  [end;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[我们也可以做一个小的优化， 如下所示，用ID INLIST的这种方式写SQL：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select * from mytable where id in(:id1,id2,...,idn);

[通过这样处理可以大大减少SQL请求的数量，从而提高性能。那如果有10000个ID，那是不是全部放在一条SQL里处理呢？答案肯定是否定的。首先大部份数据库都会有SQL长度和IN里个数的限制，如ORACLE的IN里就不允许超过1000个值。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[另外当前数据库一般都是采用基于成本的优化规则，当IN数量达到一定值时有可能改变SQL执行计划，从索引访问变成全表访问，这将使性能急剧变化。随着SQL中IN的里面的值个数增加，SQL的执行计划会更复杂，占用的内存将会变大，这将会增加服务器CPU及内存成本。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[评估在IN里面一次放多少个值还需要考虑应用服务器本地内存的开销，有并发访问时要计算本地数据使用周期内的并发上限，否则可能会导致内存溢出。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[综合考虑，一般IN里面的值个数超过20个以后性能基本没什么太大变化，也特别说明不要超过100，超过后可能会引起执行计划的不稳定性及增加数据库CPU及内存成本，这个需要专业DBA评估。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3.3、设置Fetch Size][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[当我们采用select从数据库查询数据时，数据默认并不是一条一条返回给客户端的，也不是一次全部返回客户端的，而是根据客户端fetch\_size参数处理，每次只返回fetch\_size条记录，当客户端游标遍历到尾部时再从服务端取数据，直到最后全部传送完成。所以如果我们要从服务端一次取大量数据时，可以加大fetch\_size，这样可以减少结果数据传输的交互次数及服务器数据准备时间，提高性能。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[以下是jdbc测试的代码，采用本地数据库，表缓存在数据库CACHE中，因此没有网络连接及磁盘IO开销，客户端只遍历游标，不做任何处理，这样更能体现fetch参数的影响：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1. [String vsql ="select \* from t\_employee";][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2. [PreparedStatement pstmt = conn.prepareStatement(vsql,ResultSet.TYPE\_FORWARD\_ONLY,ResultSet.CONCUR\_READ\_ONLY);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3. [pstmt.setFetchSize(1000);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
4. [ResultSet rs = pstmt.executeQuery(vsql);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
5. [int cnt = rs.getMetaData().getColumnCount();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
6. [Object o;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
7. [while (rs.next()) \{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
8. [ for (int i = 1; i <= cnt; i++) \{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
9. [ o = rs.getObject(i);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
10. [ \}][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
11. [\}][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[测试示例中的employee表有100000条记录，每条记录平均长度135字节][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[以下是测试结果，对每种fetchsize测试5次再取平均值：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

<table style="border-spacing:0px;color:rgb(51,51,51);font-family:'-apple-system', 'SF UI Text', Arial, 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'WenQuanYi Micro Hei', sans-serif, SimHei, SimSun;font-size:14px;background-color:rgb(255,255,255);"> 
 <tbody> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">fetchsize</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">&nbsp;elapse_time（s）</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">1</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">20.516</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">2</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">11.34</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">4</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">6.894</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">8</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">4.65</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">16</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">3.584</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">32</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">2.865</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">64</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">2.656</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">128</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">2.44</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">256</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">2.765</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">512</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">3.075</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">1024</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">2.862</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">2048</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">2.722</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">4096</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">2.681</a></td> 
 </tr> 
 <tr> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">8192</a></td> 
 <td><a href="https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&amp;mid=2247483684&amp;idx=1&amp;sn=f5abc60e696b2063e43cd9ccb40df101&amp;chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&amp;mpshare=1&amp;scene=1&amp;srcid=0606XGHeBS4RBZloVv786wBY#rd" rel="nofollow">2.715</a></td> 
 </tr> 
 </tbody> 
</table>

[![640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 6][]][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[Oracle jdbc fetchsize默认值为10，由上测试可以看出fetchsize对性能影响还是比较大的，但是当fetchsize大于100时就基本上没有影响了。fetchsize并不会存在一个最优的固定值，因为整体性能与记录集大小及硬件平台有关。根据测试结果建议当一次性要取大量数据时这个值设置为100左右，不要小于40。注意，fetchsize不能设置太大，如果一次取出的数据大于JVM的内存会导致内存溢出，所以建议不要超过1000，太大了也没什么性能提高，反而可能会增加内存溢出的危险。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[注：图中fetchsize在128以后会有一些小的波动，这并不是测试误差，而是由于resultset填充到具体对像时间不同的原因，由于resultset已经到本地内存里了，所以估计是由于CPU的L1,L2 Cache命中率变化造成，由于变化不大，所以笔者也未深入分析原因。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[iBatis的SqlMapping配置文件可以对每个SQL语句指定fetchsize大小，如下所示：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1. [<select id="getAllProduct" resultMap="HashMap" fetchSize="1000">][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2. [select \* from employee][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3. [</select>][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3.4、使用存储过程][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[大型数据库一般都支持存储过程，合理的利用存储过程也可以提高系统性能。如你有一个业务需要将A表的数据做一些加工然后更新到B表中，但是又不可能一条SQL完成，这时你需要如下3步操作：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[a：将A表数据全部取出到客户端；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[b：计算出要更新的数据；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[c：将计算结果更新到B表。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果采用存储过程你可以将整个业务逻辑封装在存储过程里，然后在客户端直接调用存储过程处理，这样可以减少网络交互的成本。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[当然，存储过程也并不是十全十美，存储过程有以下缺点：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[a、不可移植性，每种数据库的内部编程语法都不太相同，当你的系统需要兼容多种数据库时最好不要用存储过程。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[b、学习成本高，DBA一般都擅长写存储过程，但并不是每个程序员都能写好存储过程，除非你的团队有较多的开发人员熟悉写存储过程，否则后期系统维护会产生问题。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[c、业务逻辑多处存在，采用存储过程后也就意味着你的系统有一些业务逻辑不是在应用程序里处理，这种架构会增加一些系统维护和调试成本。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[d、存储过程和常用应用程序语言不一样，它支持的函数及语法有可能不能满足需求，有些逻辑就只能通过应用程序处理。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[e、如果存储过程中有复杂运算的话，会增加一些数据库服务端的处理成本，对于集中式数据库可能会导致系统可扩展性问题。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[f、为了提高性能，数据库会把存储过程代码编译成中间运行代码(类似于java的class文件)，所以更像静态语言。当存储过程引用的对像(表、视图等等)结构改变后，存储过程需要重新编译才能生效，在24\*7高并发应用场景，一般都是在线变更结构的，所以在变更的瞬间要同时编译存储过程，这可能会导致数据库瞬间压力上升引起故障(Oracle数据库就存在这样的问题)。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[个人观点：普通业务逻辑尽量不要使用存储过程，定时性的ETL任务或报表统计函数可以根据团队资源情况采用存储过程处理。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3.5、优化业务逻辑][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[要通过优化业务逻辑来提高性能是比较困难的，这需要程序员对所访问的数据及业务流程非常清楚。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[举一个案例：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[某移动公司推出优惠套参，活动对像为VIP会员并且2010年1，2，3月平均话费20元以上的客户。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[那我们的检测逻辑为：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果我们修改业务逻辑为:][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1.  [select avg(money) as avg\_money from bill where phone\_no='13988888888' and date between '201001' and '201003';][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2.  [if avg\_money>20 then][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3.  [begin][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
4.  [ select vip\_flag from member where phone\_no='13988888888';][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
5.  [ if vip\_flag=true then][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
6.  [ begin][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
7.  [ 执行套参();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
8.  [ end;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
9.  [end;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[通过这样可以减少一些判断vip\_flag的开销，平均话费20元以下的用户就不需要再检测是否VIP了。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果程序员分析业务，VIP会员比例为1%，平均话费20元以上的用户比例为90%，那我们改成如下：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1.  [select vip\_flag from member wherephone\_no='13988888888';][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2.  [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3.  [if vip\_flag=true then][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
4.  [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
5.  [begin][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
6.  [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
7.  [ select avg(money) as avg\_money frombill where phone\_no='13988888888' and date between '201001' and '201003';][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
8.  [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
9.  [ if avg\_money>20 then][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
10. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
11. [ begin][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
12. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
13. [ 执行套参();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
14. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
15. [ end;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
16. [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
17. [end;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[这样就只有1%的VIP会员才会做检测平均话费，最终大大减少了SQL的交互次数。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[以上只是一个简单的示例，实际的业务总是比这复杂得多，所以一般只是高级程序员更容易做出优化的逻辑，但是我们需要有这样一种成本优化的意识。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3.6、使用ResultSet游标处理记录][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[现在大部分Java框架都是通过jdbc从数据库取出数据，然后装载到一个list里再处理，list里可能是业务Object，也可能是hashmap。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[由于JVM内存一般都小于4G，所以不可能一次通过sql把大量数据装载到list里。为了完成功能，很多程序员喜欢采用分页的方法处理，如一次从数据库取1000条记录，通过多次循环搞定，保证不会引起JVM Out of memory问题。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[以下是实现此功能的代码示例，t\_employee表有10万条记录，设置分页大小为1000：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1. [d1 = Calendar.getInstance().getTime();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2. [vsql = "select count(\*) cnt from t\_employee";][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3. [pstmt = conn.prepareStatement(vsql);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
4. [ResultSet rs = pstmt.executeQuery();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
5. [Integer cnt = 0;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
6. [while (rs.next()) \{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
7. [ cnt = rs.getInt("cnt");][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
8. [\}][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
9. [Integer lastid=0;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
10. [Integer pagesize=1000;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
11. [System.out.println("cnt:" + cnt);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
12. [String vsql = "select count(\*) cnt from t\_employee";][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
13. [PreparedStatement pstmt = conn.prepareStatement(vsql);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
14. [ResultSet rs = pstmt.executeQuery();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
15. [Integer cnt = 0;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
16. [while (rs.next()) \{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
17. [ cnt = rs.getInt("cnt");][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
18. [\}][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
19. [Integer lastid = 0;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
20. [Integer pagesize = 1000;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
21. [System.out.println("cnt:" + cnt);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
22. [for (int i = 0; i <= cnt / pagesize; i++) \{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
23. [ vsql = "select \* from (select \* from t\_employee where id>? order by id) where rownum<=?";][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
24. [ pstmt = conn.prepareStatement(vsql);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
25. [ pstmt.setFetchSize(1000);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
26. [ pstmt.setInt(1, lastid);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
27. [ pstmt.setInt(2, pagesize);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
28. [ rs = pstmt.executeQuery();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
29. [ int col\_cnt = rs.getMetaData().getColumnCount();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
30. [ Object o;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
31. [ while (rs.next()) \{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
32. [ for (int j = 1; j <= col\_cnt; j++) \{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
33. [ o = rs.getObject(j);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
34. [ \}][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
35. [ lastid = rs.getInt("id");][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
36. [ \}][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
37. [ rs.close();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
38. [ pstmt.close();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
39. [\}][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[以上代码实际执行时间为6.516秒][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[很多持久层框架为了尽量让程序员使用方便，封装了jdbc通过statement执行数据返回到resultset的细节，导致程序员会想采用分页的方式处理问题。实际上如果我们采用jdbc原始的resultset游标处理记录，在resultset循环读取的过程中处理记录，这样就可以一次从数据库取出所有记录。显著提高性能。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[这里需要注意的是，采用resultset游标处理记录时，应该将游标的打开方式设置为FORWARD\_READONLY模式(ResultSet.TYPE\_FORWARD\_ONLY,ResultSet.CONCUR\_READ\_ONLY)，否则会把结果缓存在JVM里，造成JVM Out of memory问题。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[代码示例：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1. [String vsql ="select \* from t\_employee";][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2. [PreparedStatement pstmt = conn.prepareStatement(vsql,ResultSet.TYPE\_FORWARD\_ONLY,ResultSet.CONCUR\_READ\_ONLY);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3. [pstmt.setFetchSize(100);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
4. [ResultSet rs = pstmt.executeQuery(vsql);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
5. [int col\_cnt = rs.getMetaData().getColumnCount();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
6. [Object o;][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
7. [while (rs.next()) \{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
8. [ for (int j = 1; j <= col\_cnt; j++) \{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
9. [ o = rs.getObject(j);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
10. [ \}][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
11. [\}][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[调整后的代码实际执行时间为3.156秒][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[从测试结果可以看出性能提高了1倍多，如果采用分页模式数据库每次还需发生磁盘IO的话那性能可以提高更多。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[iBatis等持久层框架考虑到会有这种需求，所以也有相应的解决方案，在iBatis里我们不能采用queryForList的方法，而应用该采用queryWithRowHandler加回调事件的方式处理，如下所示：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1.  [MyRowHandler myrh=new MyRowHandler();][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2.  [sqlmap.queryWithRowHandler("getAllEmployee", myrh);][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3.  [ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
4.  [class MyRowHandler implements RowHandler \{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
5.  [ public void handleRow(Object o) \{ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
6.  [ //todo something][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
7.  [ \}][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
8.  [\}][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[iBatis的queryWithRowHandler很好的封装了resultset遍历的事件处理，效果及性能与resultset遍历一样，也不会产生JVM内存溢出。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[4、减少数据库服务器CPU运算][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[4.1、使用绑定变量][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[绑定变量是指SQL中对变化的值采用变量参数的形式提交，而不是在SQL中直接拼写对应的值。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1.  [非绑定变量写法：Select \* from employee where id=1234567][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2.  [绑定变量写法：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3.  [Select \* from employee where id=?][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
4.  [Preparestatement.setInt(1,1234567)][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[Java中Preparestatement就是为处理绑定变量提供的对像，绑定变量有以下优点：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[1、防止SQL注入][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2、提高SQL可读性][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[3、提高SQL解析性能，不使用绑定变更我们一般称为硬解析，使用绑定变量我们称为软解析。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[第1和第2点很好理解，做编码的人应该都清楚，这里不详细说明。关于第3点，到底能提高多少性能呢，下面举一个例子说明：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[假设有这个这样的一个数据库主机：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2个4核CPU ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[100块磁盘，每个磁盘支持IOPS为160][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[业务应用的SQL如下：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[select \* from table where pk=?][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[这个SQL平均4个IO（3个索引IO+1个数据IO）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[IO缓存命中率75%（索引全在内存中，数据需要访问磁盘）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[SQL硬解析CPU消耗：1ms  （常用经验值）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[SQL软解析CPU消耗：0.02ms（常用经验值）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[假设CPU每核性能是线性增长，访问内存Cache中的IO时间忽略，要求计算系统对如上应用采用硬解析与采用软解析支持的每秒最大并发数：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[从以上计算可以看出，不使用绑定变量的系统当并发达到8000时会在CPU上产生瓶颈，当使用绑定变量的系统当并行达到16000时会在磁盘IO上产生瓶颈。所以如果你的系统CPU有瓶颈时请先检查是否存在大量的硬解析操作。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[使用绑定变量为何会提高SQL解析性能，这个需要从数据库SQL执行原理说明，一条SQL在Oracle数据库中的执行过程如下图所示：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[![640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 7][]][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[当一条SQL发送给数据库服务器后，系统首先会将SQL字符串进行hash运算，得到hash值后再从服务器内存里的SQL缓存区中进行检索，如果有相同的SQL字符，并且确认是同一逻辑的SQL语句，则从共享池缓存中取出SQL对应的执行计划，根据执行计划读取数据并返回结果给客户端。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果在共享池中未发现相同的SQL则根据SQL逻辑生成一条新的执行计划并保存在SQL缓存区中，然后根据执行计划读取数据并返回结果给客户端。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[为了更快的检索SQL是否在缓存区中，首先进行的是SQL字符串hash值对比，如果未找到则认为没有缓存，如果存在再进行下一步的准确对比，所以要命中SQL缓存区应保证SQL字符是完全一致，中间有大小写或空格都会认为是不同的SQL。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果我们不采用绑定变量，采用字符串拼接的模式生成SQL,那么每条SQL都会产生执行计划，这样会导致共享池耗尽，缓存命中率也很低。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[一些不使用绑定变量的场景：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[a、数据仓库应用，这种应用一般并发不高，但是每个SQL执行时间很长，SQL解析的时间相比SQL执行时间比较小，绑定变量对性能提高不明显。数据仓库一般都是内部分析应用，所以也不太会发生SQL注入的安全问题。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[b、数据分布不均匀的特殊逻辑，如产品表，记录有1亿，有一产品状态字段，上面建有索引，有审核中，审核通过，审核未通过3种状态，其中审核通过9500万，审核中1万，审核不通过499万。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[要做这样一个查询：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select count(*) from product where status=?

[采用绑定变量的话，那么只会有一个执行计划，如果走索引访问，那么对于审核中查询很快，对审核通过和审核不通过会很慢；如果不走索引，那么对于审核中与审核通过和审核不通过时间基本一样；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[对于这种情况应该不使用绑定变量，而直接采用字符拼接的方式生成SQL，这样可以为每个SQL生成不同的执行计划，如下所示。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1.  [select count(\*) from product where status='approved'; //不使用索引][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2.  [select count(\*) from product where status='tbd'; //不使用索引][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3.  [select count(\*) from product where status='auditing';//使用索引][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[4.2、合理使用排序][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[Oracle的排序算法一直在优化，但是总体时间复杂度约等于nLog(n)。普通OLTP系统排序操作一般都是在内存里进行的，对于数据库来说是一种CPU的消耗，曾在PC机做过测试，单核普通CPU在1秒钟可以完成100万条记录的全内存排序操作，所以说由于现在CPU的性能增强，对于普通的几十条或上百条记录排序对系统的影响也不会很大。但是当你的记录集增加到上万条以上时，你需要注意是否一定要这么做了，大记录集排序不仅增加了CPU开销，而且可能会由于内存不足发生硬盘排序的现象，当发生硬盘排序时性能会急剧下降，这种需求需要与DBA沟通再决定，取决于你的需求和数据，所以只有你自己最清楚，而不要被别人说排序很慢就吓倒。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[以下列出了可能会发生排序操作的SQL语法：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1.  [Order by][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2.  [Group by][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3.  [Distinct][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
4.  [Exists子查询][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
5.  [Not Exists子查询][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
6.  [In子查询][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
7.  [Not In子查询][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[Union（并集），Union All也是一种并集操作，但是不会发生排序，如果你确认两个数据集不需要执行去除重复数据操作，那请使用Union All 代替Union。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

1.  [Minus（差集）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
2.  [Intersect（交集）][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]
3.  [Create Index][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[Merge Join，这是一种两个表连接的内部算法，执行时会把两个表先排序好再连接，应用于两个大表连接的操作。如果你的两个表连接的条件都是等值运算，那可以采用Hash Join来提高性能，因为Hash Join使用Hash 运算来代替排序的操作。具体原理及设置参考SQL执行计划优化专题。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[4.3、减少比较操作][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[我们SQL的业务逻辑经常会包含一些比较操作，如a=b，a<b之类的操作，对于这些比较操作数据库都体现得很好，但是如果有以下操作，我们需要保持警惕：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[Like模糊查询，如下所示：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

a like ‘%abc%’

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[Like模糊查询对于数据库来说不是很擅长，特别是你需要模糊检查的记录有上万条以上时，性能比较糟糕，这种情况一般可以采用专用Search或者采用全文索引方案来提高性能。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[不能使用索引定位的大量In List，如下所示：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

a in (:1,:2,:3,…,:n) ----n>20

[如果这里的a字段不能通过索引比较，那数据库会将字段与in里面的每个值都进行比较运算，如果记录数有上万以上，会明显感觉到SQL的CPU开销加大，这个情况有两种解决方式：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[a、  将in列表里面的数据放入一张中间小表，采用两个表Hash Join关联的方式处理；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[b、  采用str2varList方法将字段串列表转换一个临时表处理，关于str2varList方法可以在网上直接查询，这里不详细介绍。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[以上两种解决方案都需要与中间表Hash Join的方式才能提高性能，如果采用了Nested Loop的连接方式性能会更差。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果发现我们的系统IO没问题但是CPU负载很高，就有可能是上面的原因，这种情况不太常见，如果遇到了最好能和DBA沟通并确认准确的原因。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[4.4、大量复杂运算在客户端处理][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[什么是复杂运算，一般我认为是一秒钟CPU只能做10万次以内的运算。如含小数的对数及指数运算、三角函数、3DES及BASE64数据加密算法等等。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果有大量这类函数运算，尽量放在客户端处理，一般CPU每秒中也只能处理1万-10万次这样的函数运算，放在数据库内不利于高并发处理。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[5、利用更多的资源][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[5.1、客户端多进程并行访问][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[多进程并行访问是指在客户端创建多个进程(线程)，每个进程建立一个与数据库的连接，然后同时向数据库提交访问请求。当数据库主机资源有空闲时，我们可以采用客户端多进程并行访问的方法来提高性能。如果数据库主机已经很忙时，采用多进程并行访问性能不会提高，反而可能会更慢。所以使用这种方式最好与DBA或系统管理员进行沟通后再决定是否采用。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[例如：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[我们有10000个产品ID，现在需要根据ID取出产品的详细信息，如果单线程访问，按每个IO要5ms计算，忽略主机CPU运算及网络传输时间，我们需要50s才能完成任务。如果采用5个并行访问，每个进程访问2000个ID，那么10s就有可能完成任务。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[那是不是并行数越多越好呢，开1000个并行是否只要50ms就搞定，答案肯定是否定的，当并行数超过服务器主机资源的上限时性能就不会再提高，如果再增加反而会增加主机的进程间调度成本和进程冲突机率。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[以下是一些如何设置并行数的基本建议：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果瓶颈在服务器主机，但是主机还有空闲资源，那么最大并行数取主机CPU核数和主机提供数据服务的磁盘数两个参数中的最小值，同时要保证主机有资源做其它任务。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果瓶颈在客户端处理，但是客户端还有空闲资源，那建议不要增加SQL的并行，而是用一个进程取回数据后在客户端起多个进程处理即可，进程数根据客户端CPU核数计算。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果瓶颈在客户端网络，那建议做数据压缩或者增加多个客户端，采用map reduce的架构处理。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[如果瓶颈在服务器网络，那需要增加服务器的网络带宽或者在服务端将数据压缩后再处理了。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[5.2、数据库并行处理][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[数据库并行处理是指客户端一条SQL的请求，数据库内部自动分解成多个进程并行处理，如下图所示：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[![640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 8][]][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[并不是所有的SQL都可以使用并行处理，一般只有对表或索引进行全部访问时才可以使用并行。数据库表默认是不打开并行访问，所以需要指定SQL并行的提示，如下所示：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

select /*+parallel(a,4)*/ * from employee;

[并行的优点：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[使用多进程处理，充分利用数据库主机资源（CPU,IO），提高性能。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[并行的缺点：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[1、单个会话占用大量资源，影响其它会话，所以只适合在主机负载低时期使用；][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2、只能采用直接IO访问，不能利用缓存数据，所以执行前会触发将脏缓存数据写入磁盘操作。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[ ][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[注：][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[1、并行处理在OLTP类系统中慎用，使用不当会导致一个会话把主机资源全部占用，而正常事务得不到及时响应，所以一般只是用于数据仓库平台。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[2、一般对于百万级记录以下的小表采用并行访问性能并不能提高，反而可能会让性能更差。][https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]

[https_mp.weixin.qq.com_s_biz_MzIxMjg4NDU1NA_mid_2247483684_idx_1_sn_f5abc60e696b2063e43cd9ccb40df101_chksm_97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38_mpshare_1_scene_1_srcid_0606XGHeBS4RBZloVv786wBY_rd]: https://mp.weixin.qq.com/s?__biz=MzIxMjg4NDU1NA==&mid=2247483684&idx=1&sn=f5abc60e696b2063e43cd9ccb40df101&chksm=97be0c01a0c98517029ff9aa280b398ab5c81fa1fcfe0e746222a3bfe75396d9eea1e249af38&mpshare=1&scene=1&srcid=0606XGHeBS4RBZloVv786wBY#rd
[640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1]: /images/20220520/8e8cdefd0f5f4cf7b8cd59e7c56de3fb.png
[0_wx_fmt_gif_wxfrom_5_wx_lazy_1]: /images/20220520/fdb67a05e1254c228d174325bafcacb1.png
[640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 1]: /images/20220520/01ee9a1f371941b6b6676eb390b46b85.png
[640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 2]: /images/20220520/52f220f143e446ad9acfc7680a4de390.png
[640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 3]: /images/20220520/7430e369e49f4d0fb08ba48bb8bee785.png
[640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 4]: /images/20220520/f856025b5fa1435c948c76e1348fa7dd.png
[640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 5]: /images/20220520/54b3bb2c33844df79c73832ef6231c6f.png
[640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 6]: /images/20220520/e53e44740fca4baf8257cb0eb94d5bc9.png
[640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 7]: /images/20220520/961b5355554c4530a4d0529f887486d0.png
[640_wx_fmt_jpeg_wxfrom_5_wx_lazy_1 8]: /images/20220520/1b74dfaed12b4823a5d9c767ee83e1bd.png