On Tue, Apr 5, 2016 at 11:30 AM, Andres Freund <andres@anarazel.de> wrote:
> On 2016-04-05 20:56:31 +0530, Amit Kapila wrote:
>> This fluctuation started appearing after commit 6150a1b0 which we have
>> discussed in another thread [1] and a colleague of mine is working on to
>> write a patch to try to revert it on current HEAD and then see the results.
>
> I don't see what that buys us. That commit is a good win on x86...
Maybe. But I wouldn't be surprised to find out that that is an
overgeneralization. Based on some results Mithun Cy showed me this
morning, I think that some of this enormous run-to-run fluctuation
that we're seeing is due to NUMA effects. So some runs we get two
things that are frequently accessed together on the same NUMA node and
other times they get placed on different NUMA nodes and then
everything sucks. I don't think we fully understand what's going on
here yet - and I think we're committing changes in this area awfully
quickly - but I see no reason to believe that x86 is immune to such
effects. They may just happen in different scenarios than what we see
on POWER.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
