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macossqliteimessage

iMessage app storage location - why is chat.db-wal updated instantly but chat.db takes awhile?

So playing around with iMessages and thinking of ways to back them up and various things.

I found their location at ~/Library/Messages.

There are three files

1. chat.db
2. chat.db-wal
3. chat.db-shm

If I run a node script that watches for file changes while sending a iMessage to someone I see chat.db-wal is changed instantly but chat.db takes awhile to update.

I would like to get the messages as soon as possible, but I am not sure I can read the .db-wal file. Anyone know if I can read that file? Or why the .db file seems to take longer to update?

Thanks.

Solution

  • Everything is fine. Your data is there. This is just how SQLite works.

    In order to support ACID transactions, where your data is guaranteed to be stored properly in the case of crashes or power-offs, SQLite first writes your data into a "write-ahead log" (the *-wal file). When the database is properly closed, or the write-ahead log gets too full, SQLite will update the database file with the contents of the log.

    SQLite, when reading, will consult the write-ahead log first, even if multiple connections are using the same database. Data in the log is still "in the database".

    SQLite should apply the log to the database as part of closing the database. If it does not, you can run PRAGMA wal_checkpoint; to manually checkpoint the log file.

    Corollary to this: do not delete the -wal file, especially if you have not cleanly closed the database last time you used it.

    More information about write-ahead logging in SQLite can be found in the SQLite documentation.