Re: Performance regression on CVS head

Tom Lane wrote:
> Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
>> I tried to repeat the DBT-2 runs with the "oldestxmin refresh" patch,
>> but to my surprise the baseline run with CVS head, without the patch,
>> behaved very differently than it did back in March.
>
>> I rerun the a shorter 1h test with CVS head from May 20th, and March 6th
>> (which is when I ran the earlier tests), and something has clearly been
>> changed between those dates that affects the test. Test run 248 is with
>> CVS checkout from May 20th, and 249 is from March 6th:
>
> May 20th is not quite my idea of "HEAD" ;-). It might be worth checking
> current code before investing any think-time on this. But having said
> that, it looks a bit like a planner problem --- if I'm reading the
> graphs correctly, I/O wait time goes through the roof, suggesting a
> change to a much less efficient plan.

I tracked this down to the patch to enable plan invalidation for SPI plans:

http://archives.postgresql.org/pgsql-committers/2007-03/msg00136.php

Apparently the vacuum causes a plan invalidation and a worse plan is
chosen. I'll dig deeper into which queries are being affected and why.
Unless someone has any better ideas.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com