Re: Odd problem with performance in duplicate database

On Mon, 2003-08-11 at 17:03, Josh Berkus wrote:
> Folks,
>
> More followup on this:
>
> The crucial difference between the two execution plans is this clause:
>
> test db has:
> ->  Seq Scan on case_clients  (cost=0.00..3673.48 rows=11274 width=11) (actual
> time=0.02..302.20 rows=8822 loops=855)
>
> whereas live db has:
> ->  Index Scan using idx_caseclients_case on case_clients  (cost=0.00..5.10
> rows=1 width=11) (actual time=0.03..0.04 rows=1 loops=471)
>
> using an enable_seqscan = false fixes this, but is obviously not a long-term
> solution.
>
> I've re-created the test system from an immediate copy of the live database,
> and checked that the the main tables and indexes were reproduced faithfully.
>
> Lowering random_page_cost seems to do the trick.  But I'm still mystified; why
> would one identical database pick a different plan than its copy?

If the databases are on different machines, maybe the postgres.conf
or pg_hba.conf files are different, and the buffer counts is affect-
ing the optimizer?

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| Ron Johnson, Jr.        Home: ron.l.johnson@cox.net           |
| Jefferson, LA  USA                                            |
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