From: | Bruno Wolff III <bruno(at)wolff(dot)to> |
---|---|
To: | Zavier Sheran <zsheran(at)yahoo(dot)com> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: slow count() |
Date: | 2005-01-28 05:38:34 |
Message-ID: | 20050128053834.GA11394@wolff.to |
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Thread: | |
Lists: | pgsql-performance |
On Thu, Jan 27, 2005 at 21:17:56 -0800,
Zavier Sheran <zsheran(at)yahoo(dot)com> wrote:
> quote from manual:
> --
> Unfortunately, there is no similarly trivial query
> that can be used to improve the performance of count()
> when applied to the entire table
> --
>
> does count(1) also cause a sequential scan of the
> entire table? It should be able to just use the
> primary keys.
No it can't just use the index file, so that an index scan will be slower
than the sequential scan unless there is a where clause restricting the
number of rows to a small fraction (about 5%) of the table.
Search the archives for if you want to read more about this.
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