To: Will Reese <wreese@rackspace.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Slow deletes in 8.1 when FKs are involved 
In-reply-to: <22780344-3C6A-474E-8101-60B8806DA152@rackspace.com> 
References: <22780344-3C6A-474E-8101-60B8806DA152@rackspace.com>
Comments: In-reply-to Will Reese <wreese@rackspace.com>
	message dated "Sun, 23 Apr 2006 21:41:14 -0500"
Date: Sun, 23 Apr 2006 23:32:39 -0400
Message-ID: <20018.1145849559@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Will Reese <wreese@rackspace.com> writes:
> ... Both servers have identical postgresql.conf settings and were  
> restored from the same 7.4 backup. Almost everything is faster on the  
> 8.1 server (mostly due to hardware), except one thing...deletes from  
> tables with many foreign keys pointing to them.

I think it's unquestionable that you have a bad FK plan in use on the
8.1 server.  Double check that you have suitable indexes on the
referencing (not referenced) columns, that you've ANALYZEd all the
tables involved, and that you've started a fresh psql session (remember
the backend tends to cache FK plans for the life of the connection).

It might help to EXPLAIN ANALYZE one of the slow deletes --- 8.1 will
break out the time spent in FK triggers, which would let you see which
one(s) are the culprit.

			regards, tom lane