Is it safe to delete sqlite's WAL file?

Question

I have a strange problem with Core Data in an iOS app where sometimes the WAL file becomes huge (~1GB). It appears there are other people with the problem (e.g. Cor

Answer 1

Couple of things:

1. You can certainly delete the WAL file. You will lose any committed transactions that haven't been checkpointed back to the main file. (Thus violating the "durability" part of ACID, but perhaps you don't care.)

2. You can control the size of the WAL file on disk with the journal_size_limit pragma (if it bothers you). You may want to manually checkpoint more often too. See "Avoiding Excessively Large WAL files" here: https://www.sqlite.org/wal.html

3. I dislike all the superstitious bashing of WAL mode. WAL mode is faster, more concurrent, and much simpler since it dispenses with the all the locking level shenanigans (and most "database is busy" problems) that go with rollback journals. WAL mode is the right choice in almost every situation. (The only place it is problematic is on flash filesystems that don't support shared memory-mapped access to files. In that case, the "unofficial" SQLITE_SHM_DIRECTORY compile directive can be used to move the .shm file to a different kind of filesystem -- e.g. tmpfs -- but this should not be a concern on iOS.)