Use of max_slot_wal_keep_size parameter

Good morning,

With our recent upgrade to PG 15, we've put the max_slot_wal_keep_size into
place, setting it about 3% lower than the size of the volume dedicated to
pg_wal. However last night we had an incident where the volume filled up
while we were performing a massive insert from one table into another.

I don't believe the replica was lagging, and we have pgbackrest configured
for async archiving, which I assume was fine. It seemed to just be a matter
of PG not cleaning up the WAL. Our understanding was that
max_slot_wal_keep_size would prevent this but perhaps it only deals with
situations where the replication slot lag is a factor?

Don.

--
Don Seiler
www.seiler.us