On Thu, May 17, 2012 16:10, Ants Aasma wrote: > On Thu, May 17, 2012 at 4:53 PM, Erik Rijkers <e...@xs4all.nl> wrote: >> The count(*) was done in the way that I showed, i.e. *after* psql had >> exited. My understanding >> is >> that, with synchronous replication 'on' and configured properly, psql could >> only return *after* >> the sync-replica had the data safely on disk. Either my understanding is >> not correct or there >> is >> a bug in postgres sync-rep. > > Commit can only return when sync-replica has the data safely on disk, > but this doesn't mean that it's visible yet. > > The sequence of events is in dot notation: > commit_command -> master_wal_sync -> replica_wal_sync -> > master_commit_visible -> commit_response > replica_wal_sync -> replica_replay_wal -> replica_commit_visible > > If you issue a select on the replica after getting a commit response > from master you can see that the query getting a snapshot races with > replay of the commit record. >
Ah yes, that makes sense. I hadn't thought of that. Thank you for that explanation. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
