Re: slow index lookup - Mailing list pgsql-performance

From Tom Lane
Subject Re: slow index lookup
Date
Msg-id 11812.1277258513@sss.pgh.pa.us
Whole thread Raw
In response to Re: slow index lookup  (Alvaro Herrera <alvherre@commandprompt.com>)
Responses Re: slow index lookup  (Anj Adu <fotographs@gmail.com>)
Re: slow index lookup  (Anj Adu <fotographs@gmail.com>)
List pgsql-performance
Alvaro Herrera <alvherre@commandprompt.com> writes:
> Excerpts from Anj Adu's message of mar jun 22 17:44:39 -0400 2010:
>> This query seems unreasonable slow on a well-indexed table (13 million
>> rows). Separate indexes are present on guardid_id , from_num and
>> targetprt columns.

> Maybe you need to vacuum or reindex?

Rethinking the set of indexes is probably a more appropriate suggestion.
Separate indexes aren't usefully combinable for a case like this --- in
principle the thing could do a BitmapAnd, but the startup time would be
pretty horrid, and the LIMIT 1 is discouraging it from trying that.
If this is an important case to optimize then you need a 3-column index.

            regards, tom lane

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