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Re: timestamp indexing

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Tobias Brox <tobias(at)nordicbet(dot)com>
Cc: Michael Fuhr <mike(at)fuhr(dot)org>, pgsql-performance(at)postgresql(dot)org
Subject: Re: timestamp indexing
Date: 2005-05-30 17:57:54
Message-ID: 24839.1117475874@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Tobias Brox <tobias(at)nordicbet(dot)com> writes:
>> What version of PostgreSQL are you using?

> Also answered in my follow-up - "not yet pg8" :)

Your followup hasn't shown up here yet, but if the query is written like
	WHERE timestampcol >= now() - interval 'something'
then the pre-8.0 planner is not capable of making a good estimate of the
selectivity of the WHERE clause.  One solution is to fold the timestamp
computation to a constant on the client side.

			regards, tom lane

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