Re: Database performance problem

Porell, Chris wrote:
> I have recently migrated a Postgres database from 7.4 running on gentoo to
> 8.1 running on SLES 10. I migrated the data using pg_dump and then running
> the SQL in psql. The old server was a dual AMD opteron 2.6 GHz machine with
> a RAID 5 array and 4GB memory. The new machine is a dual dual-core AMD
> Opteron 2.6GHz with RAID 1 and 16GB memory. Several reports are taking way
> too long to run. I snagged a SELECT from one of the reports. It is a
> fairly complex query with 4 joins, which unfortunately I can't share. I can
> say that the plan for the query on both machines looks nearly identical -
> that is there are no sequential scans happening on the old DB server that
> aren't also happening on the new server.
>
> The total database size is less that 1GB.
>
> On my new DB server, it takes about 27 seconds for this query to run. On
> the old server, it takes 2 seconds.
>
> I've changed shared_buffers, checkpoint_segments, effective_cache_size and
> random_page_cost in an attempt to improve performance. That has helped a
> little, but 27 seconds is still almost 14 times what it used to take. I
> feel I'm missing something obvious, and I don't have much experience with
> Postgres.
>
> Any ideas?

I assume you have analyzed after you reloaded the data? If so, can you
get a explain analzye of the query in question from both the old server
and the new server and post that to the list.