Re: Repeated PredicateLockRelation calls during seqscan

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