From: | Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com> |
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To: | Bruno BAGUETTE <pgsql-ml(at)baguette(dot)net> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Increase performance of a UNION query that thakes |
Date: | 2004-02-06 15:52:24 |
Message-ID: | 20040206074755.M86604@megazone.bigpanda.com |
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Thread: | |
Lists: | pgsql-performance |
On Fri, 6 Feb 2004, Bruno BAGUETTE wrote:
> I was thinking that a index on lower(substr(l_name, 1, 1)) and another
> index on lower(substr(org_name, 1, 1)) should gives better performances.
> When I've to create theses two indexes, it seems like this is not
> allowed :
>
> levure=> CREATE INDEX firstchar_lastname_idx ON
> people(lower(substr(l_name, 1, 1)));
> ERROR: parser: parse error at or near "(" at character 59
In 7.4, I believe you would say
on people((lower(substr(l_name,1,1))))
but I'm not sure that index would really help in practice.
> Do you have another idea to get better performances ?
In addition to what Tom said, the row estimates look suspiciously default.
You mention vacuuming, but do you ever analyze the tables?
Also, what do you have sort_mem set to?
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Previous Message | Tom Lane | 2004-02-06 15:28:24 | Re: Increase performance of a UNION query that thakes 655.07 msec to be runned ? |