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Re: reducing random_page_cost from 4 to 2 to force index scan

From: Nathan Boley <npboley(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Jesper Krogh <jesper(at)krogh(dot)cc>, pgsql-performance(at)postgresql(dot)org
Subject: Re: reducing random_page_cost from 4 to 2 to force index scan
Date: 2011-05-16 19:10:37
Message-ID: BANLkTimOEkO55L4g8u7-zyXwTnxFDjhpbA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
> The accesses to an index are far more likely to be clustered than the
> accesses to the underlying table, because the index is organized in a
> way that's application-meaningful and the table not so much.

So, to clarify, are you saying that if query were actually requesting
rows uniformly random, then there would be no reason to suspect that
index accesses would have hotspots? It seems like the index structure
( ie, the top node in b-trees ) could also get in the way.

Best,
Nathan

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