From: Jeremy Haile <jhaile@fastmail.fm>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: Slow inner join, but left join is fast
Date: Wed, 10 Jan 2007 13:38:24 -0500
Message-ID: <1168454304.25047.1168597535@webmail.messagingengine.com> (raw)
In-Reply-To: <14865.1168454295@sss.pgh.pa.us>
References: <1168445842.5566.1168570133@webmail.messagingengine.com>
<10060.1168449344@sss.pgh.pa.us>
<1168453218.22654.1168592237@webmail.messagingengine.com>
<14865.1168454295@sss.pgh.pa.us>
I'm pretty sure it didn't analyze in between - autovac is turned off
and I ran the test multiple times before posting.
But since I can't reproduce it anymore, I can't be 100% sure. And it
certainly doesn't make sense that the estimate for the index scan would
change based on an unrelated join condition.
If I ever get it to happen again, I'll be more careful and repost if it
is a real issue. Thanks for pointing me in the right direction!
On Wed, 10 Jan 2007 13:38:15 -0500, "Tom Lane" <tgl@sss.pgh.pa.us> said:
> "Jeremy Haile" <jhaile@fastmail.fm> writes:
> > I still don't understand why the inner join would be so different from
> > the left join prior to the analyze.
>
> Are you sure you hadn't analyzed in between? Or maybe autovac did it
> for you? The reason for the plan change is the change from estimating
> 1 row matching the transaction_date range constraint, to estimating lots
> of them, and the join type away up at the top would surely not have
> affected that.
>
> regards, tom lane
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Cc: jhaile@fastmail.fm, tgl@sss.pgh.pa.us
Subject: Re: Slow inner join, but left join is fast
In-Reply-To: <1168454304.25047.1168597535@webmail.messagingengine.com>
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