From: Alvaro Herrera <alvherre@commandprompt.com>
To: Steve <cheetah@tanabi.org>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-patches@postgreSQL.org
Subject: Re: [HACKERS] choose_bitmap_and again (was Re: [PERFORM] Strangely Variable Query Performance)
Date: Mon, 16 Apr 2007 19:01:04 -0400
Message-ID: <20070416230104.GY5658@alvh.no-ip.org> (raw)
In-Reply-To: <Pine.GSO.4.64.0704161805060.593@kittyhawk.tanabi.org>
References: <Pine.GSO.4.64.0704122025450.17955@kittyhawk.tanabi.org>
<12360.1176436194@sss.pgh.pa.us>
<Pine.GSO.4.64.0704122354430.17955@kit!tyhawk.tanabi.org>
<26399.1176504501@sss.pgh.pa.us>
<20070413232409.GI27255@alvh.no-ip.org>
<7772.1176574886@sss.pgh.pa.us>
<23414.1176588173@sss.pgh.pa.us>
<Pine.GSO.4.64.0704141830490.17955@kittyhawk.tanabi.org>
<26103.1176613862@sss.pgh.pa.us>
<Pine.GSO.4.64.0704161805060.593@kittyhawk.tanabi.org>
Steve wrote:
> >Can you find any cases where it makes a worse choice than before?
> >Another thing to pay attention to is whether the planning time gets
> >noticeably worse. If we can't find any cases where it loses badly
> >on those measures, I'll feel comfortable in applying it...
>
> Okay, here's the vedict; all the "extremely slow" queries (i.e.
> queries that took more than 30 seconds and upwards of several minutes to
> complete) are now running in the realm of reason. In fact, most queries
> that took between 1 and 4 minutes are now down to taking about 9 seconds
> which is obviously a tremendous improvement.
>
> A few of the queries that were taking 9 seconds or less are
> "slightly slower" -- meaning a second or two slower. However most of them
> are running at the same speed they were before, or better.
>
> So I'd say as far as I can tell with my application and my
> dataset, this change is solid and an obvious improvement.
Maybe it would be interesting to see in detail those cases that got a
bit slower, to further tweak the heuristic if necessary. Is the extra
time, time spent in planning or in execution?
--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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To: pgsql-performance@postgresql.org
Cc: alvherre@commandprompt.com, cheetah@tanabi.org, tgl@sss.pgh.pa.us, pgsql-patches@postgreSQL.org
Subject: Re: [HACKERS] choose_bitmap_and again (was Re: [PERFORM] Strangely Variable Query Performance)
In-Reply-To: <20070416230104.GY5658@alvh.no-ip.org>
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