I use journal_mode=WAL and have periods of checkpoint starvation (complicated 
reasons) so I'm looking to prune the -wal file but in less blunt way than 

Behaviorally I want SQLITE_CHECKPOINT_PASSIVE *and then* if required -wal 
content < journal_size_limit, to do the truncation a la 

SQLITE_CHECKPOINT_PASSIVE gives me the best-effort checkpointing, but in the 
best case I don't get -wal shrinkage. SQLITE_CHECKPOINT_TRUNCATE is more of an 
aggressive do-it-now-wait-if-necessary which gets me the shrinkage behavior, 
but with *required*-effort rather than best-effort. I'd really like both -- 
best-effort checkpoint AND best-effort truncate.

sqlite3WalClose does exactly what I want (the key bits)

    sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE)
    sqlite3WalCheckpoint(pWal, db, SQLITE_CHECKPOINT_PASSIVE,...)
    sqlite3OsFileControlHint(pWal->pDbFd, SQLITE_FCNTL_PERSIST_WAL, &bPersist)
    if (bPersist) { if (pWal->mxWalSize>=0) { walLimitSize(pWal, 0) } }

But AFAICT this is only called when PRAGMA journal_mode changes to not WAL or 
the pager cache is closed when via sqlite3_close(). I'm a long running process 
with connection caching and associated prepared statements so torching the 
connection to trigger this isn't optimal.

Can I indirectly get this behavior if I open then immediately close a 

I think I can sorta approximate this it if I disable the busy-handler, do 
SQLITE_CHECKPOINT_TRUNCATE, ignore Busy/Locked errors and restore the 
busy-handler before returning, but that's merely 'sorta' -- ugly on several 

I don't see any way to directly try to best-effort truncate the -wal file e.g.

    sqlite3_wal_checkpoint_v2(db, NULL, SQLITE_CHECKPOINT_PASSIVE, NULL, NULL))
    sqlite3_file_control(db, NULL, SQLITE_FCNTL_TRUNCATE_WAL, NULL)

That would be ideal. Let's me handle both checkpoint'ing and truncation in 
low-impact best-effort manners. 

    - Howard
sqlite-users mailing list

Reply via email to