8.2rc1 (much) slower than 8.2dev?

Hi List,

We've been doing some benchmarks lately (one of them made it to the
PostgreSQL frontpage) with postgresql 8.2 dev (cvs checkout of 3 june
2006). But we prefer of course to run a more production-like version and
installed postgresql 8.2rc1.

As it turns out after a dump/restore (to go from 820 to 822), copying
the configuration files doing a fresh 'vacuumdb -z' (z is analyze) and
'clusterdb' the RC1 processes about 50% *less* (webpage)requests than
the 8.2dev we had, on the same machine/linux kernel/etc. On all
cpu-configurations and loads we throw at it. Since its a read-mostly
database the location on disk should matter only very slightly.

For instance, with the system currently at hand it peaks at about 20
concurrent clients in pg8.2 dev with 465407 requests processed in a 10
minuten timeframe. 8.2rc1 can only achieve 332499 requests in that same
time frame with the same load and has a peak of 335995 with 35
concurrent clients (but with 30 it only reached 287624). And we see the
same for all loads we throw at them.

So either I'm missing something, there is a (significant enough)
difference in how the tables where analyzed or there have been some
code-changes since then to change the behaviour and thereby decreasing
performance in our set-up.

Preferably I'd load the statistics from the 8.2-dev database in the
8.2-rc1 one, but a simple insert or copy-statement won't work due to the
'anyarray'-fields of pg_statistic, will it?

I'll run another analyze on the database to see if that makes any
difference, but after that I'm not sure what to check first to figure
out where things go wrong?

Best regards,

Arjen van der Meijden
Tweakers.net