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

On Thu, 24 May 2012, Robert Haas wrote:

> On Thu, May 24, 2012 at 1:42 PM, Sergey Koposov <koposov(at)ast(dot)cam(dot)ac(dot)uk> wrote:
>> I guess there is nothing catastrophically wrong with that, but still I'm
>> very suprised that you get severe locking problems (factor of two slow-down)
>> when running parallel read-only transactions.
>
> Me, too. How many concurrent connections are you running, and does
> your working set exceed shared_buffers? Can you provide a
> self-contained reproducible test case?

The last tests I've been doing were with 8 connections.
And the working set is roughly 30Gig, which is ~ 3x the shared buffers.
(but ~ 50% of RAM).

Regarding the test-case, I'll try to see whether I can still observe the
same slowing down if I chop the main table by a factor of few, so I can
put the data somewhere for download.

S

*****************************************************
Sergey E. Koposov, PhD, Research Associate
Institute of Astronomy, University of Cambridge
Madingley road, CB3 0HA, Cambridge, UK
Tel: +44-1223-337-551 Web: http://www.ast.cam.ac.uk/~koposov/