To: Jeff Frost <jeff@frostconsultingllc.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Index usage problem on 8.3.3 
In-reply-to: <490A5DCB.9060403@frostconsultingllc.com> 
References: <490A4EBE.9030804@frostconsultingllc.com>
	<13272.1225413116@sss.pgh.pa.us>
	<490A56C1.8020804@frostconsultingllc.com>
	<14519.1225415657@sss.pgh.pa.us>
	<490A5DCB.9060403@frostconsultingllc.com>
Comments: In-reply-to Jeff Frost <jeff@frostconsultingllc.com>
	message dated "Thu, 30 Oct 2008 18:22:19 -0700"
Date: Thu, 30 Oct 2008 21:27:58 -0400
Message-ID: <14766.1225416478@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Jeff Frost <jeff@frostconsultingllc.com> writes:
> Tom Lane wrote:
>> Okay.  What that means is that the indexes were created on data that had
>> already been inserted and updated to some extent, resulting in
>> HOT-update chains that turned out to be illegal for the new indexes.
>> The way we deal with this is to mark the indexes as not usable by any
>> query that can still see the dead HOT-updated tuples.

> Any idea why I don't see it on 8.3.4?

I think it's more likely some small difference in your test conditions
than any real version-to-version difference.  In particular I think the
"still see" test might be influenced by the ages of transactions running
concurrently.

			regards, tom lane