On Tue, Oct 7, 2014 at 4:30 PM, Andres Freund <and...@2ndquadrant.com> wrote: > On 2014-10-07 17:22:18 +0300, Heikki Linnakangas wrote: >> FWIW, I liked Ilya's design. Before going to sleep, store the lock ID in >> shared memory. When you wake up, clear it. That should be cheap enough to >> have it always enabled. And it can easily be extended to other "waits", e.g. >> when you're waiting for input from client. > > I think there's a few locks where that's interesting. But in my > experience many slowdowns aren't caused by actual waits, but because of > cacheline contention. And for that the number of acquisitions is much > more relevant than the waiting. The primary example for this is probably > the procarray lock.
I would say, that to see particular lwlockid 50 times in 100 samples or to see it 50 times one after another or see it only 2 times, provides good and representative information for DBA. At least better than nothing. > >> I don't think counting the number of lock acquisition is that interesting. >> It doesn't give you any information on how long the waits were, for >> example. > > Sure, that's a separate thing that we should be able to answer. The point is that a lot of short waits sometimes could be as worse as one long wait. That is why it is important, but I thing propper sampling provides good estimation for this. > > Greetings, > > Andres Freund > > -- > Andres Freund http://www.2ndQuadrant.com/ > PostgreSQL Development, 24x7 Support, Training & Services -- Ilya Kosmodemiansky, PostgreSQL-Consulting.com tel. +14084142500 cell. +4915144336040 i...@postgresql-consulting.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
