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Re: increasing collapse_limits?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: increasing collapse_limits?
Date: 2011-04-30 17:38:38
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Lists: pgsql-hackers
Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> Actually we had to solve a issue with slow SELECT. The problem was in
> low value of JOIN_COLLAPSE_LIMITS. Can we increase a default of this
> value. I checked some complex query, and planner needed about 200ms
> for JOIN_COLLAPSE_LIMIT = 16. So some around 12 can be well.

I'd like to see a rather larger survey of cases before changing that.
Also, amount of memory consumed is at least as large a concern here
as runtime.

			regards, tom lane

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