Date: Thu, 7 Jul 2011 17:21:59 -0400
From: Dan Ports <drkp@csail.mit.edu>
To: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>, pgsql-hackers@postgresql.org
Subject: Re: SSI atomic commit
Message-ID: <20110707212159.GF76634@csail.mit.edu>
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	<4E159B5C020000250003F063@gw.wicourts.gov>
	<4E160005.1020300@enterprisedb.com>
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We should also apply the attached patch, which corrects a minor issue
with the conditions for flagging transactions that could potentially
make a snapshot unsafe.

There's a small window wherein a transaction is committed but not yet
on the finished list, and we shouldn't flag it as a potential conflict
if so. We can also skip adding a doomed transaction to the list of
possible conflicts because we know it won't commit.

This is not really a related issue, but Kevin and I found it while
looking into this issue, and it was included in the patch we sent out.

Dan

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

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*** a/src/backend/storage/lmgr/predicate.c
--- b/src/backend/storage/lmgr/predicate.c
***************
*** 1669,1676 **** RegisterSerializableTransactionInt(Snapshot snapshot)
  			 othersxact != NULL;
  			 othersxact = NextPredXact(othersxact))
  		{
! 			if (!SxactIsOnFinishedList(othersxact) &&
! 				!SxactIsReadOnly(othersxact))
  			{
  				SetPossibleUnsafeConflict(sxact, othersxact);
  			}
--- 1676,1684 ----
  			 othersxact != NULL;
  			 othersxact = NextPredXact(othersxact))
  		{
! 			if (!SxactIsCommitted(othersxact)
! 				&& !SxactIsDoomed(othersxact)
! 				&& !SxactIsReadOnly(othersxact))
  			{
  				SetPossibleUnsafeConflict(sxact, othersxact);
  			}

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