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Re: effective_cache_size patch

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: pgsql-patches(at)postgresql(dot)org
Subject: Re: effective_cache_size patch
Date: 2004-11-04 19:13:05
Message-ID: 27927.1099595585@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-patches
Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> I enclose a doc patch for the effective_cache_size parameter in
> runtime.sgml: efcdoc.patch

Applied after translation into English ;-)

> Also, another minor patch which prevents effective_cache_size and
> random_page_cost from being set incorrectly: plancost.patch
> - previously it was possible to set effective_cache_size to 0, which
> would then be ignored and treated as 1 at run-time, so set minimum to 1
> and remove test at run-time.

I applied the guc.c change but did not remove the run-time test, just
to be on the safe side.

> - previously it was possible to set random_page_cost as a fractional
> value between 0 and 1, which screws up planner estimation, so set
> minimum value of 1 (i.e. random cost same as sequential cost).

Did not apply this.  People sometimes use random_cost < 1 to force the
planner to pick index scans.  Ideally this shouldn't be necessary...

			regards, tom lane

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