From: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Date: Fri, 26 Nov 2010 17:16:12 +0000 (-0600)
Subject: Progress on using conflict lists rather than conflict pointers.
X-Git-Url: http://git.postgresql.org/gitweb/static/We?a=commitdiff_plain;h=97d806a9b543fdde222e461d97af9b0f141d4772;p=users%2Fkgrittn%2Fpostgres.git

Progress on using conflict lists rather than conflict pointers.
This commit brings us back to having no false negatives, although
the false positive rate is still high.
---

diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index bc481d5232..b73fcaf77a 100644
--- a/src/backend/storage/lmgr/predicate.c
+++ b/src/backend/storage/lmgr/predicate.c
@@ -1930,7 +1930,7 @@ ReleasePredicateLocks(const bool isCommit)
 	 */
 	needToClear = false;
 	LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
-	if (MySerializableXact->xmin == SerializableGlobalXmin)
+	if (TransactionIdEquals(MySerializableXact->xmin, SerializableGlobalXmin))
 	{
 		Assert(SerializableGlobalXminCount > 0);
 		if (--SerializableGlobalXminCount == 0)
@@ -2186,7 +2186,9 @@ CheckForSerializableConflictOut(const bool valid, const Relation relation,
 		xid = HeapTupleHeaderGetXmin(tuple->t_data);
 	}
 
-	/* Bail out if xid is too early to be a conflict. */
+	/*
+	 * Find top level xid.  Bail out if xid is too early to be a conflict.
+	 */
 	if (TransactionIdPrecedes(xid, TransactionXmin))
 		return;
 	xid = SubTransGetTopmostTransaction(xid);
@@ -2540,12 +2542,19 @@ OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader,
 
 	failure = false;
 
+	/*
+	 * Check for already-committed writer with rw-conflict out flagged.
+	 * This means that the reader must immediately fail.
+	 */
+	if (SxactIsCommitted(writer) && (writer->flags & SXACT_FLAG_CONFLICT_OUT))
+		failure = true;
+
 	/*
 	 * Check whether the reader has become a pivot with a committed writer.
 	 * If so, we must roll back unless every in-conflict either committed
 	 * before the writer committed or is READ ONLY and overlaps the writer.
 	 */
-	if (SxactIsCommitted(writer) && !SxactIsReadOnly(reader))
+	if (!failure && SxactIsCommitted(writer) && !SxactIsReadOnly(reader))
 	{
 		conflict = (RWConflict)
 			SHMQueueNext(&reader->inConflicts,
@@ -2555,7 +2564,7 @@ OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader,
 		{
 			if (!SxactIsRolledBack(conflict->sxactIn)
 				&& (!SxactIsCommitted(conflict->sxactIn)
-				 || conflict->sxactIn->commitSeqNo > writer->commitSeqNo)
+				 || conflict->sxactIn->commitSeqNo >= writer->commitSeqNo)
 				&& (!SxactIsReadOnly(conflict->sxactIn)
 					|| conflict->sxactIn->lastCommitBeforeSnapshot >= writer->commitSeqNo))
 			{