Re: 9.2beta1, parallel queries, ReleasePredicateLocks, CheckForSerializableConflictIn in the oprofile

On Fri, May 25, 2012 at 10:30 AM, Merlin Moncure <mmoncure@gmail.com> wrote:
> I think what's happening here is that the buffer partitions don't help
> (in fact, they hurt) in the presence of multiple concurrent scans that
> are operating on approximately the same data.  Sooner or later the
> scans line up on each other and start binding when reassigning lock
> tags (which take out up to two ordered exclusive lwlocks). This is on
> the read side, so the buffer access strategy is zero help (I confirmed
> this off list).

This theory is seeming fairly plausible - how can we test it?

How about trying it with synchronize_seqscans = off?  If the
synchronized-seqscan logic is causing contention on the buf mapping
locks and individual buffer locks, that should fix it.

--
Robert Haas
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