From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Michael Glaesemann <grzm(at)seespotcode(dot)net> |
Cc: | "Phoenix Kiula" <phoenix(dot)kiula(at)gmail(dot)com>, "PG-General Mailing List" <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: Timestamp indexes (why ">" or "between" does not use index?) |
Date: | 2008-02-16 15:39:39 |
Message-ID: | 19464.1203176379@sss.pgh.pa.us |
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Lists: | pgsql-general |
Michael Glaesemann <grzm(at)seespotcode(dot)net> writes:
> The planner will choose a seq scan if it thinks that it will be
> faster than using an index: if based on its statistics it thinks a
> large portion of rows will match the criteria, a seq scan may well be
> faster than an index scan.
> Have you analyzed recently?
If you've never analyzed at all, the default assumptions will
discourage the planner from using an indexscan for a one-sided
inequality condition (like "x > constant"). On the other hand,
it usually will use an indexscan for a range inequality (like
"x > constant1 and x < constant2", or a BETWEEN construct).
If you do have ANALYZE stats then it all depends on what fraction of
the column's range is selected by the inequality or range condition.
regards, tom lane
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