From: Tom Lane <tgl@sss.pgh.pa.us>
To: Ian Westmacott <ianw@intellivid.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: merge>hash>loop
Date: Fri, 14 Apr 2006 12:13:25 -0400
Message-ID: <10000.1145031205@sss.pgh.pa.us> (raw)
In-Reply-To: <1145029009.3422.31.camel@spectre.intellivid.com>
References: <1145029009.3422.31.camel@spectre.intellivid.com>
Ian Westmacott <ianw@intellivid.com> writes:
> I have this query, where PG (8.1.2) prefers Merge Join over Hash Join
> over Nested Loop. However, this order turns out to increase in
> performance. I was hoping someone might be able to shed some light on
> why PG chooses the plans in this order, and what I might do to
> influence it otherwise. Thanks,
Reducing random_page_cost would influence it to prefer the nestloop.
However, I doubt you're ever going to get really ideal results for
this query --- the estimated row counts are too far off, and the
WHERE conditions are sufficiently bizarre that there's not much hope
that they'd ever be much better.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, ianw@intellivid.com
Subject: Re: merge>hash>loop
In-Reply-To: <10000.1145031205@sss.pgh.pa.us>
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