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. >> 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. -- 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
