From 35e5767503e1292c321acd7af0953d75ee969f30 Mon Sep 17 00:00:00 2001
From: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Date: Sat, 27 Nov 2010 10:24:02 -0600
Subject: [PATCH] Clean up rolled-back transaction immediately. Minor LW
 locking adjustments and comment improvements also included.

---
 src/backend/storage/lmgr/predicate.c | 33 ++++++++++++++++------------
 1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index 37d9c207c5..79d0216a46 100644
--- a/src/backend/storage/lmgr/predicate.c
+++ b/src/backend/storage/lmgr/predicate.c
@@ -217,6 +217,7 @@
 #define SxactIsCommitted(sxact) (((sxact)->flags & SXACT_FLAG_COMMITTED) != 0)
 #define SxactIsRolledBack(sxact) (((sxact)->flags & SXACT_FLAG_ROLLED_BACK) != 0)
 #define SxactIsReadOnly(sxact) (((sxact)->flags & SXACT_FLAG_READ_ONLY) != 0)
+#define SxactHasConflictOut(sxact) (((sxact)->flags & SXACT_FLAG_CONFLICT_OUT) != 0)
 
 #define SxactCommittedBefore(sxactPivotOut, sxactOther) \
 	((!TransactionIdIsValid((sxactOther)->finishedBefore)) \
@@ -1859,6 +1860,7 @@ ReleasePredicateLocks(const bool isCommit)
 		Assert(!SxactIsRolledBack((SERIALIZABLEXACT *) MySerializableXact));
 		Assert(SxactIsCommitted((SERIALIZABLEXACT *) MySerializableXact));
 		MySerializableXact->commitSeqNo = ++LastSerializableCommitSeqNo;
+		/* Recognize implicit read-only transaction (commit without write). */
 		if (!(MySerializableXact->flags & SXACT_FLAG_DID_WRITE))
 			MySerializableXact->flags |= SXACT_FLAG_READ_ONLY;
 	}
@@ -1915,11 +1917,12 @@ ReleasePredicateLocks(const bool isCommit)
 
 	LWLockRelease(SerializableXactHashLock);
 
-	/* Add this to the list of transactions to check for later cleanup. */
 	LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE);
-	SHMQueueInsertBefore(FinishedSerializableTransactions,
-						 (SHM_QUEUE *) &(MySerializableXact->finishedLink));
-	LWLockRelease(SerializableFinishedListLock);
+
+	/* Add this to the list of transactions to check for later cleanup. */
+	if (isCommit)
+		SHMQueueInsertBefore(FinishedSerializableTransactions,
+							 (SHM_QUEUE *) &(MySerializableXact->finishedLink));
 
 	/*
 	 * Check whether it's time to clean up old transactions. This can only be
@@ -1929,17 +1932,22 @@ ReleasePredicateLocks(const bool isCommit)
 	 * was launched.
 	 */
 	needToClear = false;
-	LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
 	if (TransactionIdEquals(MySerializableXact->xmin, SerializableGlobalXmin))
 	{
+		LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
 		Assert(SerializableGlobalXminCount > 0);
 		if (--SerializableGlobalXminCount == 0)
 		{
 			SetNewSerializableGlobalXmin();
 			needToClear = true;
 		}
+		LWLockRelease(SerializableXactHashLock);
 	}
-	LWLockRelease(SerializableXactHashLock);
+
+	LWLockRelease(SerializableFinishedListLock);
+
+	if (!isCommit)
+		ReleaseOneSerializableXact((SERIALIZABLEXACT *) MySerializableXact);
 
 	if (needToClear)
 		ClearOldPredicateLocks();
@@ -1978,6 +1986,7 @@ ClearOldPredicateLocks(void)
 											 SerializableGlobalXmin))
 		{
 			LWLockRelease(SerializableXactHashLock);
+			SHMQueueDelete(&(finishedSxact->finishedLink));
 			ReleaseOneSerializableXact(finishedSxact);
 			LWLockAcquire(SerializableXactHashLock, LW_SHARED);
 		}
@@ -2005,7 +2014,6 @@ ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact)
 
 	Assert(sxact != NULL);
 	Assert(SxactIsRolledBack(sxact) || SxactIsCommitted(sxact));
-	Assert(SxactIsOnFinishedList(sxact));
 
 	LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED);
 	predlock = (PREDICATELOCK *)
@@ -2036,10 +2044,9 @@ ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact)
 
 		LWLockAcquire(partitionLock, LW_EXCLUSIVE);
 		SHMQueueDelete(targetLink);
-
 		/*
-		 * No need to do retail removal from transaction object; it's going
-		 * away.
+		 * No need to do retail removal of predicate locks from transaction
+		 * object; it's going away.
 		 */
 		hash_search_with_hash_value(PredicateLockHash, &tag,
 								PredicateLockHashCodeFromTargetHashCode(&tag,
@@ -2053,8 +2060,6 @@ ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact)
 	}
 	LWLockRelease(SerializablePredicateLockListLock);
 
-	SHMQueueDelete(&(sxact->finishedLink));
-
 	sxidtag.xid = sxact->topXid;
 	LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
 
@@ -2235,7 +2240,7 @@ CheckForSerializableConflictOut(const bool valid, const Relation relation,
 	 */
 	if (SxactIsReadOnly((SERIALIZABLEXACT *) MySerializableXact)
 		&& SxactIsCommitted(sxact)
-		&& (sxact->flags & SXACT_FLAG_CONFLICT_OUT) == 0)
+		&& !SxactHasConflictOut(sxact))
 	{
 		/* Read-only transaction will appear to run first.	No conflict. */
 		LWLockRelease(SerializableXactHashLock);
@@ -2572,7 +2577,7 @@ OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader,
 	 * 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))
+	if (SxactIsCommitted(writer) && SxactHasConflictOut(writer))
 		failure = true;
 
 	/*
-- 
2.39.5