From: Tom Lane <tgl@sss.pgh.pa.us>
To: Merlin Moncure <merlin.moncure@rcsonline.com>
Cc: pgsql-performance@postgresql.org
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] bitmap scan issues 8.1 devel
Date: Wed, 17 Aug 2005 17:54:36 -0400
Message-ID: <17374.1124315676@sss.pgh.pa.us> (raw)
In-Reply-To: <6EE64EF3AB31D5448D0007DD34EEB3417DD11C@Herge.rcsinc.local>
References: <6EE64EF3AB31D5448D0007DD34EEB3417DD11C@Herge.rcsinc.local>
"Merlin Moncure" <merlin.moncure@rcsonline.com> writes:
> Doing some testing on upcoming 8.1 devel and am having serious issues
> with new bitmap index scan feature. It is easy to work around (just
> disable it) but IMO the planner is using it when a regular index scan
> should be strongly favored.
I think blaming the bitmap code is the wrong response. What I see in
your example is that the planner doesn't know what the LIMIT value is,
and accordingly is favoring a plan that isn't going to get blown out of
the water if the LIMIT is large. I'd suggest not parameterizing the
LIMIT.
(But hmm ... I wonder if we could use estimate_expression_value for
LIMIT items, instead of handling only simple Consts as the code does
now?)
regards, tom lane
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, merlin.moncure@rcsonline.com, pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] bitmap scan issues 8.1 devel
In-Reply-To: <17374.1124315676@sss.pgh.pa.us>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox