Re: Why is that index not used?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Michael Monnerie <michael(dot)monnerie(at)is(dot)it-management(dot)at>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: Why is that index not used?
Date: 2009-01-21 15:51:40
Message-ID: 2612.1232553100@sss.pgh.pa.us
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-admin

Michael Monnerie <michael(dot)monnerie(at)is(dot)it-management(dot)at> writes:
> Can somebody explain me why on the last line, "dbmail_physmessage",
> there is a seq. scan going on and no index used?

Because it chose to use a hash instead. Given the rowcounts I don't
think that's wrong, but if you want to see the other plan you can try
setting enable_hashjoin = off (and maybe enable mergejoin = off if
it goes to a merge join next).

As for your other question, the reason it likes the dbmail_messages_1
index is probably that it's a lot smaller than dbmail_messages_7.
The only thing I'm seeing that seems curious is that when forced to
use dbmail_messages_7, it isn't using what seems to be an available
index condition.

regards, tom lane

In response to

Responses

Browse pgsql-admin by date

  From Date Subject
Next Message Vladimir Rusinov 2009-01-21 16:51:10 Re: PostgreSQL monitoring
Previous Message Alvaro Herrera 2009-01-21 15:40:46 Re: Why is that index not used?