| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Dan Ports <drkp(at)csail(dot)mit(dot)edu>, pgsql-hackers(at)postgresql(dot)org, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov> |
| Subject: | Re: Repeated PredicateLockRelation calls during seqscan |
| Date: | 2011-06-22 18:19:44 |
| Message-ID: | 4E023240.6070100@enterprisedb.com |
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| Lists: | pgsql-hackers |
On 22.06.2011 17:28, Tom Lane wrote:
> Dan Ports<drkp(at)csail(dot)mit(dot)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
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