From: Scott Marlowe <scott.marlowe@gmail.com>
To: Gregory Stark <stark@enterprisedb.com>
Cc: Luke Lonergan <llonergan@greenplum.com>
Cc: Carlo Stonebanks <stonec.register@sympatico.ca>
Cc: pgsql-performance@postgresql.org
Subject: Re: random_page_costs - are defaults of 4.0 realistic for SCSI RAID 1
Date: Mon, 10 Sep 2007 16:59:38 -0500
Message-ID: <dcc563d10709101459o11451c33y8cab7dcf1e00a93f@mail.gmail.com> (raw)
In-Reply-To: <87y7fekxga.fsf@oxford.xeocode.com>
References: <C30AF4C7.4230B%llonergan@greenplum.com>
<87y7fekxga.fsf@oxford.xeocode.com>
On 9/10/07, Gregory Stark <stark@enterprisedb.com> wrote:
>
> "Luke Lonergan" <llonergan@greenplum.com> writes:
>
> > Should be a lot higher, something like 10-15 is approximating accurate.
>
> Most people's experience is that due to Postgres underestimating the benefits
> of caching lowering the random_page_cost is helpful.
Quite often the real problem is that they have effective_cache_size
too small, and they use random_page_cost to get the planner to switch
to index scans on small tables. With a large effective_cache_size and
small to moderate table (i.e. it fits in memory pretty handily) the
planner seems much better in the last few major releases about picking
an index over a sequential scan.
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To: pgsql-performance@postgresql.org
Cc: scott.marlowe@gmail.com, stark@enterprisedb.com, llonergan@greenplum.com, stonec.register@sympatico.ca
Subject: Re: random_page_costs - are defaults of 4.0 realistic for SCSI RAID 1
In-Reply-To: <dcc563d10709101459o11451c33y8cab7dcf1e00a93f@mail.gmail.com>
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