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. -- Álvaro Herrera <alvhe...@commandprompt.com> The PostgreSQL Company - Command Prompt, Inc. PostgreSQL Replication, Consulting, Custom Development, 24x7 support -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
