From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | The Hermit Hacker <scrappy(at)hub(dot)org>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: How to get around LIKE inefficiencies?] |
Date: | 2000-11-06 02:48:45 |
Message-ID: | 200011060248.VAA08902@candle.pha.pa.us |
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Lists: | pgsql-hackers |
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > Sorry to be getting in here late. Have you tried CLUSTER?
>
> Prolly won't help much. I think what he's getting burnt by
> is that the planner thinks that an indexscan based on the
> LIKE 'http://www.postgresql.org/%' condition will be extremely
> selective --- it has no idea that most of the URLs in his table
> will match that prefix. It's ye same olde nonuniform-distribution
> problem; until we have better statistics, there's not much hope
> for a non-kluge solution.
But I think it will help. There will be lots of index lookups, but they
will be sequential in the heap, not random over the heap.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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