On 12/12/16 22:42, Andres Freund wrote: > Hi, > > On 2016-12-10 23:10:19 +0100, Petr Jelinek wrote: >> Hi, >> First one is outright bug, which has to do with how we track running >> transactions. What snapbuild basically does while doing initial snapshot >> is read the xl_running_xacts record, store the list of running txes and >> then wait until they all finish. The problem with this is that >> xl_running_xacts does not ensure that it only logs transactions that are >> actually still running (to avoid locking PGPROC) so there might be xids >> in xl_running_xacts that already committed before it was logged. > > I don't think that's actually true? Notice how LogStandbySnapshot() > only releases the lock *after* the LogCurrentRunningXacts() iff > wal_level >= WAL_LEVEL_LOGICAL. So the explanation for the problem you > observed must actually be a bit more complex :( >
Hmm, interesting, I did see the transaction commit in the WAL before the xl_running_xacts that contained the xid as running. I only seen it on production system though, didn't really manage to easily reproduce it locally. -- Petr Jelinek http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
