Re: upgraded to pgsql 8.2.4, getting worse performance then 7.4.x

Douglas J Hunley <doug(at)hunley(dot)homeip(dot)net> writes:
> ... We dumped their db, removed pgsql, installed the 8.2.4
> rpms from postgresql.org, did an initdb, and the pg_restored their data. It's
> been about a week now, and the customer is complaining that in their testing,
> they are seeing a 30% /decrease/ in general performance.

Well, you've definitely blown it on transferring the config-file
settings --- a quick look says that shared_buffers, work_mem, and
max_fsm_pages are all still default in the 8.2 config file.
Don't be frightened off by the "KB/MB" usages in the 8.2 file ---
you can still write "shared_buffers = 25000" if you'd rather specify
it in number of buffers than in megabytes.

There are some things you *did* transfer that I find pretty
questionable, like "enable_mergejoin = false". There are very major
differences between the 7.4 and 8.2 planners, so you need to revisit
the tests that led you to do that.

Another thing that seems strange is that the 8.2 config file does not
seem to have been processed by initdb --- or did you explicitly comment
out the settings it made?

Another thing to check is whether you ANALYZEd the new database after
loading data; a pg_dump/reload sequence doesn't do that.

regards, tom lane