通过 Elasticsearch 实现聚合检索

超、凢脫俗 2022-09-08 06:19 198阅读 0赞

*  [1 普通聚合分析][1]
    
     *  [1.1 直接聚合统计][1.1]
     *  [1.2 先检索, 再聚合][1.2 _]
     *  [1.3 扩展: fielddata和keyword的聚合比较][1.3 _ fielddata_keyword]
 *  [2 嵌套聚合][2]
    
     *  [2.1 先分组, 再聚合统计][2.1 _]
     *  [2.2 先分组, 再统计, 最后排序][2.2 _ _]
     *  [2.3 先分组, 组内再分组, 然后统计、排序][2.3 _ _]
 *  [版权声明][Link 1]

# 1 普通聚合分析 #

## 1.1 直接聚合统计 ##

**(1) 计算每个tag下的文档数量, 请求语法:**

GET book_shop/it_book/_search
    {
        "size": 0,    			// 不显示命中(hits)的所有文档信息
        "aggs": {
            "group_by_tags": {	// 聚合结果的名称, 需要自定义(复制时请去掉此注释)
                "terms": {
                    "field": "tags"
                }
            }
        }
    }

**(2) 发生错误:**

说明: 索引book\_shop的mapping映射是ES自动创建的, 它把tag解析成了text类型, 在发起对tag的聚合请求后, 将抛出如下错误:

{
        "error": {
            "root_cause": [
                {
                    "type": "illegal_argument_exception",
                    "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [tags] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead."
                }
            ],
            "type": "search_phase_execution_exception",
            "reason": "all shards failed",
            "phase": "query",
            "grouped": true,
            "failed_shards": [......]
        },
        "status": 400
    }

**(3) 错误分析:**

> 错误信息: `Set fielddata=true on [xxxx] ......`  
> 错误分析: 默认情况下, Elasticsearch 对 text 类型的字段(field)禁用了 fielddata;  
> text 类型的字段在创建索引时会进行分词处理, 而聚合操作必须基于字段的原始值进行分析;  
> 所以如果要对 text 类型的字段进行聚合操作, 就需要存储其原始值 —— 创建mapping时指定`fielddata=true`, 以便通过反转倒排索引(即正排索引)将索引数据加载至内存中.

**(4) 解决方案一: 对text类型的字段开启fielddata属性:**

*  将要分组统计的text field(即tags)的fielddata设置为true:
    
        PUT book_shop/_mapping/it_book
        {
            "properties": {
                "tags": {
                    "type": "text",
                    "fielddata": true
                }
            }
        }
 *  可参考官方文档进行设置:  
    [https://www.elastic.co/guide/en/elasticsearch/reference/6.6/fielddata.html][https_www.elastic.co_guide_en_elasticsearch_reference_6.6_fielddata.html]. 成功后的结果如下:
    
        {
          "acknowledged": true
        }
 *  再次统计, 得到的结果如下:
    
        {
            "took": 153,
            "timed_out": false,
            "_shards": {
                "total": 5,
                "successful": 5,
                "skipped": 0,
                "failed": 0
            },
            "hits": {
                "total": 4,
                "max_score": 0.0,
                "hits": []
            },
            "aggregations": {
                "group_by_tags": {
                    "doc_count_error_upper_bound": 0,
                    "sum_other_doc_count": 6,
                    "buckets": [
                        {
                            "key": "java",
                            "doc_count": 3
                        },
                        {
                            "key": "程",
                            "doc_count": 2
                        },
                        ......
                    ]
                }
            }
        }

**(5) 解决方法二: 使用内置keyword字段:**

*  开启fielddata将占用大量的内存.
 *  Elasticsearch 5.x 版本开始支持通过text的内置字段keyword作精确查询、聚合分析:
    
        GET shop/it_book/_search
        {
            "size": 0,
            "aggs": {
                "group_by_tags": {
                    "terms": {
                        "field": "tags.keyword"	// 使用text类型的内置keyword字段
            	    }
            	}
            }
        }

## 1.2 先检索, 再聚合 ##

**(1) 统计name中含有“jvm”的图书中每个tag的文档数量, 请求语法:**

GET book_shop/it_book/_search
    {
        "query": {
            "match": { "name": "jvm" }
        }, 
        "aggs": {
            "group_by_tags": {  // 聚合结果的名称, 需要自定义. 下面使用内置的keyword字段: 
                "terms": { "field": "tags.keyword" }
            }
        }
    }

**(2) 响应结果:**

{
      "took" : 7,
      "timed_out" : false,
      "_shards" : {
        "total" : 5,
        "successful" : 5,
        "skipped" : 0,
        "failed" : 0
      },
      "hits" : {
        "total" : 1,
        "max_score" : 0.64072424,
        "hits" : [
          {
            "_index" : "book_shop",
            "_type" : "it_book",
            "_id" : "2",
            "_score" : 0.64072424,
            "_source" : {
              "name" : "深入理解Java虚拟机：JVM高级特性与最佳实践",
              "author" : "周志明",
              "category" : "编程语言",
              "desc" : "Java图书领域公认的经典著作",
              "price" : 79.0,
              "date" : "2013-10-01",
              "publisher" : "机械工业出版社",
              "tags" : [
                "Java",
                "虚拟机",
                "最佳实践"
              ]
            }
          }
        ]
      },
      "aggregations" : {
        "group_by_tags" : {
          "doc_count_error_upper_bound" : 0,
          "sum_other_doc_count" : 0,
          "buckets" : [
            {
              "key" : "Java",
              "doc_count" : 1
            },
            {
              "key" : "最佳实践",
              "doc_count" : 1
            },
            {
              "key" : "虚拟机",
              "doc_count" : 1
            }
          ]
        }
      }
    }

## 1.3 扩展: fielddata和keyword的聚合比较 ##

*  为某个 text 类型的字段开启fielddata字段后, 聚合分析操作会对这个字段的所有分词分别进行聚合, 获得的结果大多数情况下并不符合我们的需求.
 *  **使用keyword内置字段, 不会对相关的分词进行聚合, 结果可能更有用.**

—— **推荐使用text类型字段的内置keyword进行聚合操作.**

# 2 嵌套聚合 #

## 2.1 先分组, 再聚合统计 ##

**(1) 先按tags分组, 再计算每个tag下图书的平均价格, 请求语法:**

GET book_shop/it_book/_search
    {
        "size": 0, 
        "aggs": {
            "group_by_tags": {
                "terms": { "field": "tags.keyword" },
                "aggs": {
                    "avg_price": {
                        "avg": { "field": "price" }
                    }
                }
            }
        }
    }

**(2) 响应结果:**

"hits" : {
        "total" : 3,
        "max_score" : 0.0,
        "hits" : [ ]
      },
      "aggregations" : {
        "group_by_tags" : {
          "doc_count_error_upper_bound" : 0,
          "sum_other_doc_count" : 0,
          "buckets" : [
            {
              "key" : "Java",
              "doc_count" : 3,
              "avg_price" : {
                "value" : 102.33333333333333
              }
            },
            {
              "key" : "编程语言",
              "doc_count" : 2,
              "avg_price" : {
                "value" : 114.0
              }
            },
            ......
          ]
        }
      }

## 2.2 先分组, 再统计, 最后排序 ##

**(1) 计算每个tag下图书的平均价格, 再按平均价格降序排序, 查询语法:**

GET book_shop/it_book/_search
    {
        "size": 0,
        "aggs": {
            "all_tags": {
                "terms": {
                    "field": "tags.keyword", 
                    "order": { "avg_price": "desc" } // 根据下述统计的结果排序
                },
                "aggs": {
                    "avg_price": {
                        "avg": { "field": "price" }
                    }
                }
            }
        }
    }

**(2) 响应结果:**

与\#2.1节内容相似, 区别在于按照价格排序显示了.

## 2.3 先分组, 组内再分组, 然后统计、排序 ##

**(1) 先按价格区间分组, 组内再按tags分组, 计算每个tags组的平均价格, 查询语法:**

GET book_shop/it_book/_search
    {
        "size": 0, 
        "aggs": {
            "group_by_price": {
                "range": {
                    "field": "price", 
                    "ranges": [
                        { "from": 00,  "to": 100 },
                        { "from": 100, "to": 150 }
                    ]
                }, 
                "aggs": {
                    "group_by_tags": {
                        "terms": { "field": "tags.keyword" }, 
                        "aggs": {
                            "avg_price": {
                                "avg": { "field": "price" }
                            }
                        }
                    }
                }
            }
        }
    }

**(2) 响应结果:**

"hits" : {
        "total" : 3,
        "max_score" : 0.0,
        "hits" : [ ]
      },
      "aggregations" : {
        "group_by_price" : {
          "buckets" : [
            {
              "key" : "0.0-100.0",    // 区间0.0-100.0
              "from" : 0.0,
              "to" : 100.0,
              "doc_count" : 1,        // 共查找到了3条文档
              "group_by_tags" : {     // 对tags分组聚合
                "doc_count_error_upper_bound" : 0,
                "sum_other_doc_count" : 0,
                "buckets" : [
                  {
                    "key" : "Java",
                    "doc_count" : 1,
                    "avg_price" : {
                      "value" : 79.0
                    }
                  },
                  ......
                ]
              }
            },
            {
              "key" : "100.0-150.0",
              "from" : 100.0,
              "to" : 150.0,
              "doc_count" : 2,
              "group_by_tags" : {
                "doc_count_error_upper_bound" : 0,
                "sum_other_doc_count" : 0,
                "buckets" : [
                  {
                    "key" : "Java",
                    "doc_count" : 2,
                    "avg_price" : {
                      "value" : 114.0
                    }
                  },
                  ......
                  }
                ]
              }
            }
          ]
        }
      }

[1]: https://www.cnblogs.com/shoufeng/p/11290669.html#1--%E6%99%AE%E9%80%9A%E8%81%9A%E5%90%88%E5%88%86%E6%9E%90
[1.1]: https://www.cnblogs.com/shoufeng/p/11290669.html#11--%E7%9B%B4%E6%8E%A5%E8%81%9A%E5%90%88%E7%BB%9F%E8%AE%A1
[1.2 _]: https://www.cnblogs.com/shoufeng/p/11290669.html#12--%E5%85%88%E6%A3%80%E7%B4%A2-%E5%86%8D%E8%81%9A%E5%90%88
[1.3 _ fielddata_keyword]: https://www.cnblogs.com/shoufeng/p/11290669.html#13--%E6%89%A9%E5%B1%95-fielddata%E5%92%8Ckeyword%E7%9A%84%E8%81%9A%E5%90%88%E6%AF%94%E8%BE%83
[2]: https://www.cnblogs.com/shoufeng/p/11290669.html#2--%E5%B5%8C%E5%A5%97%E8%81%9A%E5%90%88
[2.1 _]: https://www.cnblogs.com/shoufeng/p/11290669.html#21--%E5%85%88%E5%88%86%E7%BB%84-%E5%86%8D%E8%81%9A%E5%90%88%E7%BB%9F%E8%AE%A1
[2.2 _ _]: https://www.cnblogs.com/shoufeng/p/11290669.html#22--%E5%85%88%E5%88%86%E7%BB%84-%E5%86%8D%E7%BB%9F%E8%AE%A1-%E6%9C%80%E5%90%8E%E6%8E%92%E5%BA%8F
[2.3 _ _]: https://www.cnblogs.com/shoufeng/p/11290669.html#23--%E5%85%88%E5%88%86%E7%BB%84-%E7%BB%84%E5%86%85%E5%86%8D%E5%88%86%E7%BB%84-%E7%84%B6%E5%90%8E%E7%BB%9F%E8%AE%A1%E3%80%81%E6%8E%92%E5%BA%8F
[Link 1]: https://www.cnblogs.com/shoufeng/p/11290669.html#%E7%89%88%E6%9D%83%E5%A3%B0%E6%98%8E
[https_www.elastic.co_guide_en_elasticsearch_reference_6.6_fielddata.html]: https://www.elastic.co/guide/en/elasticsearch/reference/6.6/fielddata.html