On Thu, Mar 15, 2012 at 10:13 PM, Alvaro Herrera <alvhe...@commandprompt.com> wrote: > > Excerpts from Simon Riggs's message of jue mar 15 19:04:41 -0300 2012: >> >> On Thu, Mar 15, 2012 at 9:54 PM, Alvaro Herrera >> <alvhe...@commandprompt.com> wrote: >> > >> > Excerpts from Simon Riggs's message of jue mar 15 18:38:53 -0300 2012: >> >> On Thu, Mar 15, 2012 at 2:26 AM, Robert Haas <robertmh...@gmail.com> >> >> wrote: >> > >> >> > But that would only make sense if >> >> > we thought that getting rid of the fsyncs would be more valuable than >> >> > avoiding the blocking here, and I don't. >> >> >> >> You're right that the existing code could use some optimisation. >> >> >> >> I'm a little tired, but I can't see a reason to fsync this except at >> >> checkpoint. >> > >> > Hang on. What fsyncs are we talking about? I don't see that the >> > multixact code calls any fsync except that checkpoint and shutdown. >> >> If a dirty page is evicted it will fsync. > > Ah, right. > >> >> Also seeing that we issue 2 WAL records for each RI check. We issue >> >> one during MultiXactIdCreate/MultiXactIdExpand and then immediately >> >> afterwards issue a XLOG_HEAP_LOCK record. The comments on both show >> >> that each thinks it is doing it for the same reason and is the only >> >> place its being done. Alvaro, any ideas why that is. >> > >> > AFAIR the XLOG_HEAP_LOCK log entry only records the fact that the row is >> > being locked by a multixact -- it doesn't record the contents (member >> > xids) of said multixact, which is what the other log entry records. >> >> Agreed. But issuing two records when we could issue just one seems a >> little strange, especially when the two record types follow one >> another so closely - so we end up queuing for the lock twice while >> holding the lock on the data block. > > Hmm, that seems optimization that could be done separately.
Oh yes, definitely not something for you to add to the main patch. Just some additional tuning to alleviate Robert's concerns. -- Simon Riggs 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