On Fri, Sep 23, 2016 at 6:50 AM, Robert Haas <robertmh...@gmail.com> wrote: > On Thu, Sep 22, 2016 at 7:44 PM, Tomas Vondra > <tomas.von...@2ndquadrant.com> wrote: >> I don't dare to suggest rejecting the patch, but I don't see how we could >> commit any of the patches at this point. So perhaps "returned with feedback" >> and resubmitting in the next CF (along with analysis of improved workloads) >> would be appropriate. > > I think it would be useful to have some kind of theoretical analysis > of how much time we're spending waiting for various locks. So, for > example, suppose we one run of these tests with various client counts > - say, 1, 8, 16, 32, 64, 96, 128, 192, 256 - and we run "select > wait_event from pg_stat_activity" once per second throughout the test. > Then we see how many times we get each wait event, including NULL (no > wait event). Now, from this, we can compute the approximate > percentage of time we're spending waiting on CLogControlLock and every > other lock, too, as well as the percentage of time we're not waiting > for lock. That, it seems to me, would give us a pretty clear idea > what the maximum benefit we could hope for from reducing contention on > any given lock might be. >
As mentioned earlier, such an activity makes sense, however today, again reading this thread, I noticed that Dilip has already posted some analysis of lock contention upthread [1]. It is clear that patch has reduced LWLock contention from ~28% to ~4% (where the major contributor was TransactionIdSetPageStatus which has reduced from ~53% to ~3%). Isn't it inline with what you are looking for? [1] - https://www.postgresql.org/message-id/CAFiTN-u-XEzhd%3DhNGW586fmQwdTy6Qy6_SXe09tNB%3DgBcVzZ_A%40mail.gmail.com -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
