Re: index scan on =, but not < ?

From: Manfred Koizar <mkoi-pg(at)aon(dot)at>
To: David Brown <time(at)bigpond(dot)net(dot)au>
Cc: "Jim C(dot) Nasby" <decibel(at)decibel(dot)org>, pgsql-performance(at)postgresql(dot)org, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Subject: Re: index scan on =, but not < ?
Date: 2005-03-17 08:12:42
Message-ID: 3oei31lc0uitgvmgfbsehm4r92ad9reas3@email.aon.at
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On Thu, 10 Mar 2005 10:24:46 +1000, David Brown <time(at)bigpond(dot)net(dot)au>
wrote:
>What concerns me is that this all depends on the correlation factor, and
>I suspect that the planner is not giving enough weight to this.

The planner does the right thing for correlations very close to 1 (and
-1) and for correlations near zero. For correlations somewhere between
0 and 1 the cost is estimated by interpolation, but it tends too much
towards the bad end, IMHO.

Servus
Manfred

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