From: Tom Lane <tgl@sss.pgh.pa.us>
To: jkapad@csd.uoc.gr
Cc: pgsql-performance@postgresql.org
Subject: Re: Problem with bitmap-index-scan plan
Date: Thu, 13 Jul 2006 18:32:58 -0400
Message-ID: <21981.1152829978@sss.pgh.pa.us> (raw)
In-Reply-To: <1152078884.44ab542441450@ermis.edu.uoc.gr>
References: <1152078884.44ab542441450@ermis.edu.uoc.gr>
jkapad@csd.uoc.gr writes:
> ... is quite reasonable.The table has 1.000.000 rows (17.242 pages). From
> pg_stat_get_blocks_fetched I can see that there were 102 page requests for
> table. So all things seem to work great here!
> But if I multiply the size of the table ten-times (10.000.000 rows - 172.414
> pages) and run the same query I get:
> ...
> which is slower even than a seq scan. Now I get that there were 131.398 page
> requests for table in order to retrieve almost 1250 tuples!Can someone explain
> why this is happening? All memory parameters are set to default.
You probably need to increase work_mem so that the bitmaps don't become
lossy ...
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, jkapad@csd.uoc.gr
Subject: Re: Problem with bitmap-index-scan plan
In-Reply-To: <21981.1152829978@sss.pgh.pa.us>
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