From: Rod Taylor <pg@rbt.ca>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@postgresql.org
Subject: Re: More thoughts about planner's cost estimates
Date: Fri, 02 Jun 2006 19:05:15 -0400
Message-ID: <1149289515.6071.211.camel@home> (raw)
In-Reply-To: <11319.1149287800@sss.pgh.pa.us>
References: <14821.1149104747@sss.pgh.pa.us>
<11319.1149287800@sss.pgh.pa.us>
> One objection to this is that after moving "off the gold standard" of
> 1.0 = one page fetch, there is no longer any clear meaning to the
> cost estimate units; you're faced with the fact that they're just an
> arbitrary scale. I'm not sure that's such a bad thing, though. For
> instance, some people might want to try to tune their settings so that
> the estimates are actually comparable to milliseconds of real time.
Any chance that the correspondence to time could be made a part of the
design on purpose and generally advise people to follow that rule? If we
could tell people to run *benchmark* and use those numbers directly as a
first approximation tuning, it could help quite a bit for people new to
PostgreSQL experiencing poor performance.
effective_cache_size then becomes essentially the last hand-set variable
for medium sized installations.
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To: pgsql-hackers@postgresql.org
Cc: pg@rbt.ca, tgl@sss.pgh.pa.us
Subject: Re: More thoughts about planner's cost estimates
In-Reply-To: <1149289515.6071.211.camel@home>
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