Message-ID: <4E023240.6070100@enterprisedb.com>
Date: Wed, 22 Jun 2011 21:19:44 +0300
From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: Dan Ports <drkp@csail.mit.edu>, pgsql-hackers@postgresql.org,
	Kevin Grittner <Kevin.Grittner@wicourts.gov>
Subject: Re: Repeated PredicateLockRelation calls during seqscan
References: <20110622045850.GN83336@csail.mit.edu>
	<29470.1308752899@sss.pgh.pa.us>
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On 22.06.2011 17:28, Tom Lane wrote:
> Dan Ports<drkp@csail.mit.edu>  writes:
>> I was looking at ExecSeqScan today and noticed that it invokes
>> PredicateLockRelation each time it's called, i.e. for each tuple
>> returned. Any reason we shouldn't skip that call if
>> rs_relpredicatelocked is already set, as in the attached patch?
>
> Why is the call in ExecSeqScan at all, and not in the node startup
> function?

It makes sense to delay it until the scan is actually started, so that 
you don't get unnecessary serialization failures if the scan is never 
actually executed. I don't know if that was Kevin's original reason for 
putting it there, but that's why I left it there.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com