On Thu, Jan 29, 2015 at 4:09 PM, Jim Nasby <jim.na...@bluetreble.com> wrote: >> The difference between the autovacuum-run vacuum and the cron-run vacuum >> is that the one running out of cron will just keep holding the lock >> until it's actually able to truncate the end of the relation, no? I >> recall discussion previously that we need a way to either support that >> in autovacuum for (a configurable set of) regular relations or come up >> with a solution that doesn't require that lock. > > AFAICT, in master, there is no difference in truncation between auto and > manual vacuum. What we do is attempt to acquire the truncation lock for up > to 5 seconds, giving up after that. Once we do have the lock, we check to > see how many pages we can actually truncate. During that check, we test > every ~20ms or so to see if someone else is waiting on our exclusive lock; > if they are we stop counting and will only truncate the relation up to that > point.
I don't think this is true, and I don't think it's been true for a long time, if ever. The difference between a manual vacuum and autovacuum is that autovacuum commits suicide when it conflicts with somebody else's lock request, and a manual vacuum doesn't. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
