Heikki Linnakangas wrote:
Tom Lane wrote:
Heikki Linnakangas <[EMAIL PROTECTED]> 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.

Ok, found it. The plan for stock-level transaction changed as a result of a lot of dead tuples in the district table.

I turned autovacuum on for the small, frequently-updated tables, and that fixed the problem.

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

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