From: | Andreas Kretschmer <akretschmer(at)spamfence(dot)net> |
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To: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: multicolumn indexes still efficient if not fully stressed? |
Date: | 2009-01-12 19:23:25 |
Message-ID: | 20090112192325.GA10675@tux |
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Lists: | pgsql-performance |
Jörg Kiegeland <kiegeland(at)ikv(dot)de> schrieb:
> Hello,
>
> I created a multicolumn index on the columns c_1,..,c_n .
> If I do use only a true subset of these columns in a SQL query, is the
> index still efficient?
> Or is it better to create another multicolumn index defined on this subset?
Create several indexes for each column, since 8.1 PG can use a so called
Bitmap Index Scan. Read more about that:
- http://www.postgresql-support.de/pgbook/node492.html
(in german, i think, you can read that)
- http://en.wikipedia.org/wiki/Bitmap_index
Andreas
--
Really, I'm not out to destroy Microsoft. That will just be a completely
unintentional side effect. (Linus Torvalds)
"If I was god, I would recompile penguin with --enable-fly." (unknown)
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