Re: [PERFORM] Slow query: bitmap scan troubles

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [PERFORM] Slow query: bitmap scan troubles
Date: 2013-01-15 19:46:39
Message-ID: 20130115194639.GG27934@momjian.us
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On Mon, Jan 14, 2013 at 12:56:37PM -0500, Tom Lane wrote:
> > The reported behavior was that the planner would prefer to
> > sequential-scan the table rather than use the index, even if
> > enable_seqscan=off. I'm not sure what the query looked like, but it
> > could have been something best implemented as a nested loop w/inner
> > index-scan.
>
> Remember also that "enable_seqscan=off" merely adds 1e10 to the
> estimated cost of seqscans. For sufficiently large tables this is not
> exactly a hard disable, just a thumb on the scales. But I don't know
> what your definition of "extremely large indexes" is.

Wow, do we need to bump up that value based on larger modern hardware?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +

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