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	Thu, 18 May 2006 09:41:23 PDT
Date: Thu, 18 May 2006 09:41:23 -0700 (PDT)
From: Stephen Byers <stephenabyers@yahoo.com>
Subject: Re: why is bitmap index chosen for this query?
To: "Steinar H. Gunderson" <sgunderson@bigfoot.com>,
	pgsql-performance@postgresql.org
In-Reply-To: <20060518155906.GA6909@uio.no>
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"Steinar H. Gunderson" <sgunderson@bigfoot.com> wrote:  
It sounds like PostgreSQL badly overestimates the cost of the index scan.
Does the table perchance fit completely into memory, without
effective_cache_size indicating that?

  Don't know the exact way to answer your question, but my initial instinct is "no way."
    select pg_relation_size('packets');
   pg_relation_size 
------------------
      19440115712

  19GB.  So it's a big table.  The query I submitted earlier returns about 13M rows and the table currently has about 38M rows.
   
   

		
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<B><I>"Steinar H. Gunderson" &lt;sgunderson@bigfoot.com&gt;</I></B> wrote:  <BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid"><BR>It sounds like PostgreSQL badly overestimates the cost of the index scan.<BR>Does the table perchance fit completely into memory, without<BR>effective_cache_size indicating that?<BR><BR></BLOCKQUOTE>  <div>Don't know the exact way to&nbsp;answer your question, but my initial instinct&nbsp;is "no way."</div>  <div>&nbsp; select pg_relation_size('packets');</div>  <div>&nbsp;pg_relation_size <BR>------------------<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 19440115712<BR></div>  <div>19GB.&nbsp; So it's a big table.&nbsp; The query I submitted earlier returns about 13M rows and the table currently has about 38M rows.</div>  <div>&nbsp;</div>  <div>&nbsp;</div><p>
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