Repeated PredicateLockRelation calls during seqscan

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?

That would save us a bit of overhead, since checking that flag is
cheaper than doing a hash lookup in the local predicate lock table
before bailing out.

Dan

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Dan R. K. Ports              MIT CSAIL                http://drkp.net/