System.err: android.database.sqlite.SQLiteCantOpenDatabaseException: unable to open database file (c

浅浅的花香味﹌ 2022-06-04 08:17 233阅读 0赞

12-08 15:10:17.278 30336 30351 E SQLiteLog: (14) cannot open file at line 31289 of \[5a3022e081\]  
12-08 15:10:17.278 30336 30351 E SQLiteLog: (14) os\_unix.c:31289: (2) open(/data/user/0/com.xxx.xxxx/k.db-wal) -  
12-08 15:10:17.278 30336 30351 E SQLiteLog: (14) unable to open database file  
12-08 15:10:17.278 30336 30351 W System.err: android.database.sqlite.SQLiteCantOpenDatabaseException: unable to open database file (code 14): , while compiling: select \* from content  
12-08 15:10:17.279 30336 30351 W System.err: at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)  
12-08 15:10:17.279 30336 30351 W System.err: at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:926)  
12-08 15:10:17.279 30336 30351 W System.err: at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:537)  
12-08 15:10:17.279 30336 30351 W System.err: at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)  
12-08 15:10:17.279 30336 30351 W System.err: at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)  
12-08 15:10:17.279 30336 30351 W System.err: at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)  
12-08 15:10:17.279 30336 30351 W System.err: at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)  
12-08 15:10:17.279 30336 30351 W System.err: at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1316)  
12-08 15:10:17.279 30336 30351 W System.err: at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1255)

12-08 15:10:17.279 30336 30351 W System.err: at com.uusafe.wrapper.model.KHelper.load(KHelper.java:417)

sqlite是支持write ahead logging(WAL)模式的，开启WAL模式可以提高写入数据库的速度，读和写之间不会阻塞，但是写与写之间依然是阻塞的，但是如果使用默认的TRUNCATE模式，当写入数据时会阻塞android中其他线程或者进程的读操作，并发降低。 相反，使用WAL可以提高并发。 由于使用WAL比ROLLBACK JOURNAL的模式减少了写的I/O，所以写入时速度较快，但是由于在读取数据时也需要读取WAL日志验证数据的正确性，所以读取数据相对要慢。当开启了WAL模式更新数据时，**会先将数据写入到\*.db-wal文件中**，而不是直接修改数据库文件，当执行checkpoint时或某个时间点才会将数据更新到数据库文件。当出现rollback也只是清除wal日志文件,而ROLLBACK JOURNAL模式，当数据有更新时，先将需要修改的数据备份到journal文件中，然后修改数据库文件，当发生rollback，从journal日志中取出数据，并修改数据库文件，然后清除journal日志。 从以上流程来看 WAL在数据更新上I/0量要小，所以写操作要快。

有些人认为网上有有效的简单解决办法直接删除，

String book\_journal = "/data/data/com.stevenhu.android.phone.ui/databases/Book.db-journal";  
File file\_journal = new File(book\_journal);  
if ( file\_journal.exists() )  
\{  
file\_journal.delete();  
\}

为什么会报错呢， 原因是手机默认开启了wal 模式， 但是我们读取的db 文件及其目录不可写， 导致，系统在进行数据库的wal 操作，打开k.db-wal 文件时， 该临时文件不能创建， 导致 执行的事物操作中断。

1.  publicboolean enableWriteAheadLogging() \{ 
2.  // make sure the database is not READONLY. WAL doesn't make sense for readonly-databases.
3.  if (isReadOnly()) \{ 
4.  returnfalse; 
5.   \} 
6.  // acquire lock - no that no other thread is enabling WAL at the same time
7.   lock(); 
8.  try \{ 
9.  if (mConnectionPool != null) \{ 
10. // already enabled
11. returntrue; 
12.  \} 
13. if (mPath.equalsIgnoreCase(MEMORY\_DB\_PATH)) \{ 
14.  Log.i(TAG, "can't enable WAL for memory databases."); 
15. returnfalse; 
16.  \} 
17. 
18. // make sure this database has NO attached databases because sqlite's write-ahead-logging
19. // doesn't work for databases with attached databases
20. if (mHasAttachedDbs) \{ 
21. if (Log.isLoggable(TAG, Log.DEBUG)) \{ 
22.  Log.d(TAG, 
23. "this database: " \+ mPath + " has attached databases. can't enable WAL."); 
24.  \} 
25. returnfalse; 
26.  \} 
27.  mConnectionPool = new DatabaseConnectionPool(this); 
28.  setJournalMode(mPath, "WAL"); 
29. returntrue; 
30.  \} finally \{ 
31.  unlock(); 
32.  \} 
33.  \}

/**
     * Open flag: Flag for {
       @link #openDatabase} to open the database file with
     * write-ahead logging enabled by default.  Using this flag is more efficient
     * than calling {
       @link #enableWriteAheadLogging}.
     *
     * Write-ahead logging cannot be used with read-only databases so the value of
     * this flag is ignored if the database is opened read-only.
     *
     * @see #enableWriteAheadLogging
     */
    public static final int ENABLE_WRITE_AHEAD_LOGGING = 0x20000000;

这些源码都说明了一个问题， 开启wal 模式需要对db 文件所在的目录可写权限。

File export = new File(path, PathHelper.EXPORT_DIR);
    Log.e("tianxuhong", "dir"+export.getAbsolutePath());
    export.setWritable(true, false);

// for app sql load flags  to readOnly
    public static final int SQL_FLAGS_READONLY = SQLiteDatabase.NO_LOCALIZED_COLLATORS|SQLiteDatabase.CONFLICT_IGNORE|SQLiteDatabase.OPEN_READONLY;

db = SQLiteDatabase.openDatabase(a, null, UGlobal.SQL_FLAGS_READONLY);