Date: Tue, 21 Jun 2016 18:15:43 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andrew Gierth <andrew@tao11.riddles.org.uk>,
	Stephen Frost <sfrost@snowman.net>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: MultiXactId error after upgrade to 9.3.4
Message-ID: <20160621221543.GA123505@alvherre.pgsql>
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="qMm9M+Fa2AknHoGS"
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20160621200922.GA106138@alvherre.pgsql>
User-Agent: Mutt/1.5.23 (2014-03-12)
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org


--qMm9M+Fa2AknHoGS
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit

Alvaro Herrera wrote:
> Robert Haas wrote:
> > On Fri, Jun 17, 2016 at 9:33 AM, Andrew Gierth
> > <andrew@tao11.riddles.org.uk> wrote:
> > >>>>>> "Robert" == Robert Haas <robertmhaas@gmail.com> writes:
> > >  >> Why is the correct rule not "check for and ignore pre-upgrade mxids
> > >  >> before even trying to fetch members"?
> > >
> > >  Robert> I entirely believe that's the correct rule, but doesn't
> > >  Robert> implementing it require a crystal balll?
> > >
> > > Why would it? Pre-9.3 mxids are identified by the combination of flag
> > > bits in the infomask, see Alvaro's patch.
> > 
> > I see the patch, but I don't see much explanation of why the patch is
> > correct, which I think is pretty scary in view of the number of
> > mistakes we've already made in this area.
> 
> ... and actually the patch fails one isolation tests in 9.3, which is
> why I haven't pushed (I haven't tested 9.4 but I suppose it should be
> the same).  I'm looking into that now.

Ah, it should have been obvious; the reason it's failing is because 9.3
and 9.4 lack commit 27846f02c176 which removed
MultiXactHasRunningRemoteMembers(), so the straight backpatch plus
conflict fixes left one GetMultiXactIdMembers call with the allow_old
flag to true.  The attached patch fixes that omission.

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

--qMm9M+Fa2AknHoGS
Content-Type: text/x-diff; charset=us-ascii
Content-Disposition: attachment; filename="locked-upgraded-93-fixup.patch"
Content-Transfer-Encoding: quoted-printable

commit 17507b2a04b8c381997410d1fe3fbaacc34f5a31=1B[m
Author:     Alvaro Herrera <alvherre@alvh.no-ip.org>
AuthorDate: Tue Jun 21 18:07:49 2016 -0400
CommitDate: Tue Jun 21 18:07:49 2016 -0400

    fixup MultiXactHasRunningRemoteMembers

diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/tr=
ansam/multixact.c
index 15de62d..efbca6f 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -1448,7 +1448,7 @@ MultiXactHasRunningRemoteMembers(MultiXactId multi)
 	int			nmembers;
 	int			i;
=20
-	nmembers =3D GetMultiXactIdMembers(multi, &members, true);
+	nmembers =3D GetMultiXactIdMembers(multi, &members, false);
 	if (nmembers <=3D 0)
 		return false;
=20
diff --git a/src/backend/utils/time/tqual.c b/src/backend/utils/time/tqual.c
index 9d7050a..931e2fb 100644
--- a/src/backend/utils/time/tqual.c
+++ b/src/backend/utils/time/tqual.c
@@ -701,7 +701,9 @@ HeapTupleSatisfiesUpdate(HeapTupleHeader tuple, Command=
Id curcid,
=20
 				if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
 				{
-					if (MultiXactHasRunningRemoteMembers(xmax))
+					if (HEAP_LOCKED_UPGRADED(tuple->t_infomask))
+						return HeapTupleMayBeUpdated;
+					else if (MultiXactHasRunningRemoteMembers(xmax))
 						return HeapTupleBeingUpdated;
 					else
 						return HeapTupleMayBeUpdated;
@@ -725,6 +727,7 @@ HeapTupleSatisfiesUpdate(HeapTupleHeader tuple, Command=
Id curcid,
=20
 				/* not LOCKED_ONLY, so it has to have an xmax */
 				Assert(TransactionIdIsValid(xmax));
+				Assert(!HEAP_LOCKED_UPGRADED(tuple->t_infomask));
=20
 				/* updating subtransaction must have aborted */
 				if (!TransactionIdIsCurrentTransactionId(xmax))

--qMm9M+Fa2AknHoGS
Content-Type: text/plain
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
MIME-Version: 1.0


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers

--qMm9M+Fa2AknHoGS--