The docs are a little unclear =>
https://sqlite.org/pragma.html#pragma_journal_size_limit
I need to disable autocheckpoint@close (for other reasons) so I'm looking for
ways to fence the -wal file. If I want to bound a database's -wal file to <=1MB
when I'm not in a transaction is it just PRAGMA journal_size_limit=1048576;?
Does this affect -wal growth *during* a transaction, i.e. if I BEGIN; ...INSERT
lots...; COMMIT will I successfully reach COMMIT? The journal_size_limit
doesn't affect *growth* of the -wal, right? Just 'at rest' size (i.e. outside
any transaction)?
As for why... I'm good with -wal growth while I do work but in some cases I've
got too much work coming and going w/o any idle period for autocheckpoint@close
to kick in. In a few cases I see huge (700MB+) -wal files when I've got no
transaction in play. I've set SQLITE_FCNTL_PERSIST_WAL=1 and want to explicitly
checkpoint similar to how sqlite does on close i.e. Passive + truncate
SQLITE_PRIVATE int sqlite3WalClose(...){
...
rc = sqlite3WalCheckpoint(pWal, db,
SQLITE_CHECKPOINT_PASSIVE, 0, 0, sync_flags, nBuf, zBuf, 0, 0
);
...
}else if( pWal->mxWalSize>=0 ){
/* Try to truncate the WAL file to zero bytes if the checkpoint
** completed and fsynced (rc==SQLITE_OK) and we are in persistent
** WAL mode (bPersist) and if the PRAGMA journal_size_limit is a
** non-negative value (pWal->mxWalSize>=0). Note that we truncate
** to zero bytes as truncating to the journal_size_limit might
** leave a corrupt WAL file on disk. */
walLimitSize(pWal, 0);
}
}
}
Is this the functional equivalent?
int limit = ...get current value via sqlite3_exec(db, "PRAGMA
journal_size_limit;")...
sqlite3_exec(db, "PRAGMA journal_size_limit=0;")
sqlite3_wal_checkpoint_v2(db, NULL, SQLITE_CHECKPOINT_PASSIVE, &size, &chkpt);
sqlite3_exec(db, "PRAGMA journal_size_limit=" + limit + ";")
Thanks,
* Howard
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