'What are the .db-shm and .db-wal extensions in Sqlite databases?
I am seeing some strange behavior with my application and the state of its database file after running some tests that close the database, delete it, and replace it with a test fixture. When I examine the database file with a tool on my debugging PC, it doesn't match what the application itself seems to be reporting. It's possible that this strange behavior is related to this bug.
I noticed that there are two files with the same base name as the database (with the normal .db extension.) The file extensions are .db-shm and .db-wal, and each is newer than the .db file's timestamp.
I assume that these are some type of temporary files. However, I am wondering if the application is terminated, shouldn't they be deleted? More importantly, I assume whatever data is stored in them is updated inside the .db file before the application is terminated by the operating system. Is this correct?
Solution 1:[1]
I do not yet have enough reputation to just add a comment to satur9nine's answer, so I'll pile on here.
As per the SQLite docs, the DB-SHM file is a Shared Memory file, only present when SQLite it running in WAL (Write-Ahead Log) mode. This is because in WAL mode, db connections sharing the same db file must all update the same memory location used as index for the WAL file, to prevent conflicts.
As for WAL file, as hinted above, it is a write log/journal, useful for commits/rollback purposes.
Solution 2:[2]
Make sure that you have closed cursor properly into SELECT operation. Sometimes SQLiteOpenHelper creates .db-shm and .db-wal extensions database due to unclosed Cursor.
Sources
This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.
Source: Stack Overflow
| Solution | Source |
|---|---|
| Solution 1 | Lutz Prechelt |
| Solution 2 | Simas Joneliunas |