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 <robertmhaas(at)gmail(dot)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.
> 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.
Álvaro Herrera <alvherre(at)commandprompt(dot)com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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