| 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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| Lists: | pgsql-hackers pgsql-performance |
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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