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List:       postgresql-general
Subject:    Re: [GENERAL] Bitmap Scan Pages
From:       Jim Nasby <decibel () decibel ! org>
Date:       2007-04-30 12:53:09
Message-ID: F752FE4D-D222-475D-8B07-275FEBBE143C () decibel ! org
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On Apr 25, 2007, at 7:36 AM, Listmail wrote:
> 	Is there a way to know how many pages were hit by a Bitmap Heap  
> scan ?
>
> 	For instance :
>
> Bitmap Heap Scan on posts
> (cost=56.71..295.24 rows=2123 width=67)
> (actual time=0.575..1.462 rows=2160 loops=1)
>
> 	I'd like to know if it hit 2160 pages (ie I should really run  
> CLUSTER) or 50 pages (ie. my table is well clustered, everything  
> cool).
> 	Since, when it's cached, it's so fast anyway I cant' tell the  
> difference, but when it's not cached, it is important.
>
> 	This would give an interesting probe for EXPLAIN ANALYZE tuning...

If you don't have anything else running in the database and you've  
got stats_block_level on, you could probably determine how many pages  
are being run by consulting the appropriate pg_statio_* view.
--
Jim Nasby                                            jim@nasby.net
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)



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