From: Andrus <eetasoft@online.ee>
To: pgsql-performance@postgresql.org
Subject: Re: Why date index is not used
Date: Fri, 9 Jun 2006 12:52:21 +0300
Message-ID: <e6bgd5$1vgk$3@news.hub.org> (raw)
References: <e69rq9$2a1b$1@news.hub.org>
<196.1149794455@sss.pgh.pa.us>
Tom,
> Because it doesn't help --- the system still has to do the sort.
It can help a lot in this case.
kuupaev is sales date
kellaaeg is sales time
Postgres can use kuupaev index to fetch first 100 rows plus a number of more
rows whose kellaaeg value is equal to kellaaeg in 100 th row. I have 500
sales per day.
So it can fetch 600 rows using index on kuupaev column.
After that it can sort those 600 rows fast.
Currently it sorts blindly all 54000 rows in table.
> You'd need a two-column index on both of the ORDER BY columns to avoid
> sorting.
Thank you. It works.
Andrus.
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Subject: Re: Why date index is not used
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