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Re: Repeated PredicateLockRelation calls during seqscan

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Dan Ports" <drkp(at)csail(dot)mit(dot)edu>, "Heikki Linnakangas" <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Repeated PredicateLockRelation calls during seqscan
Date: 2011-06-22 22:08:40
Message-ID: 4E022198020000250003EAC0@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-hackers
Dan Ports <drkp(at)csail(dot)mit(dot)edu> wrote:
 
> Note that this hadn't been a reasonable option until last week
> when we added the check for non-MVCC snapshots, since there are
> lots of things that use heap scans but SeqScan is the only
> (currently-existing) one we want to lock.
 
That is the sort of thing that I tended to notice going through the
backtraces from heap access I mentioned in another post, and is most
likely the reason the call landed where it did.  The MVCC snapshot
tests are then a game-changer.  It would be nice to find a way not
to acquire the relation lock if the node is never used, though.
 
> I am rather uneasy about making changes here unless we can be
> absolutely certain they're right...
 
Yeah....
 
-Kevin

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