diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index 27c4af9..09c757f 100644
--- a/src/backend/storage/lmgr/predicate.c
+++ b/src/backend/storage/lmgr/predicate.c
@@ -374,12 +374,6 @@ int			max_predicate_locks_per_page;		/* set by guc.c */
 static PredXactList PredXact;
 
 /*
- * This provides a pool of RWConflict data elements to use in conflict lists
- * between transactions.
- */
-static RWConflictPoolHeader RWConflictPool;
-
-/*
  * The predicate locking hash tables are in shared memory.
  * Each backend keeps pointers to them.
  */
@@ -471,6 +465,15 @@ static void OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *read
 /*------------------------------------------------------------------------*/
 
 /*
+ * Test whether a hash table is empty.
+ * I didn't find any function in dynamic hash supports the requirement.
+ */
+#define hash_table_empty(hashp)	\
+			(hash_get_num_entries(hashp) == 0)
+
+/*------------------------------------------------------------------------*/
+
+/*
  * Does this relation participate in predicate locking? Temporary and system
  * relations are exempt, as are materialized views.
  */
@@ -573,6 +576,14 @@ CreatePredXact(void)
 
 	SHMQueueDelete(&ptle->link);
 	SHMQueueInsertBefore(&PredXact->activeList, &ptle->link);
+
+	/*
+	 * NOTE: We don't need to clean the HTAB, because all of its elements
+	 *		 has been released before.
+	 */
+	Assert(hash_table_empty(ptle->inConflictsTab));
+	Assert(hash_table_empty(ptle->outConflictsTab));
+
 	return &ptle->sxact;
 }
 
@@ -635,60 +646,55 @@ NextPredXact(SERIALIZABLEXACT *sxact)
 static bool
 RWConflictExists(const SERIALIZABLEXACT *reader, const SERIALIZABLEXACT *writer)
 {
-	RWConflict	conflict;
+	bool found;
 
 	Assert(reader != writer);
 
 	/* Check the ends of the purported conflict first. */
 	if (SxactIsDoomed(reader)
-		|| SxactIsDoomed(writer)
-		|| SHMQueueEmpty(&reader->outConflicts)
-		|| SHMQueueEmpty(&writer->inConflicts))
+		|| SxactIsDoomed(writer))
 		return false;
 
-	/* A conflict is possible; walk the list to find out. */
-	conflict = (RWConflict)
-		SHMQueueNext(&reader->outConflicts,
-					 &reader->outConflicts,
-					 offsetof(RWConflictData, outLink));
-	while (conflict)
-	{
-		if (conflict->sxactIn == writer)
-			return true;
-		conflict = (RWConflict)
-			SHMQueueNext(&reader->outConflicts,
-						 &conflict->outLink,
-						 offsetof(RWConflictData, outLink));
-	}
+	hash_search(reader->outConflictsTab,
+				&writer,
+				HASH_FIND,
+				&found);
 
-	/* No conflict found. */
-	return false;
+	return found;
 }
 
 static void
 SetRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer)
 {
 	RWConflict	conflict;
+	bool		found;
 
 	Assert(reader != writer);
 	Assert(!RWConflictExists(reader, writer));
 
-	conflict = (RWConflict)
-		SHMQueueNext(&RWConflictPool->availableList,
-					 &RWConflictPool->availableList,
-					 offsetof(RWConflictData, outLink));
-	if (!conflict)
-		ereport(ERROR,
+	conflict = (RWConflict)hash_search(reader->outConflictsTab,
+										&writer,
+										HASH_ENTER_NULL,
+										&found);
+	if (!conflict){
+		ereport(ERROR, 
 				(errcode(ERRCODE_OUT_OF_MEMORY),
-				 errmsg("not enough elements in RWConflictPool to record a read/write conflict"),
-				 errhint("You might need to run fewer transactions at a time or increase max_connections.")));
-
-	SHMQueueDelete(&conflict->outLink);
+				 errmsg("insert to outRWconflicts hash table failed")));
+	}
+	conflict->sxactOut = reader;
+	conflict->sxactIn = writer;
 
+	conflict = (RWConflict)hash_search(writer->inConflictsTab,
+										&reader,
+										HASH_ENTER_NULL,
+										&found);
+	if (!conflict){
+		ereport(ERROR, 
+				(errcode(ERRCODE_OUT_OF_MEMORY),
+				 errmsg("insert to inRWconflicts hash table failed")));
+	}
 	conflict->sxactOut = reader;
 	conflict->sxactIn = writer;
-	SHMQueueInsertBefore(&reader->outConflicts, &conflict->outLink);
-	SHMQueueInsertBefore(&writer->inConflicts, &conflict->inLink);
 }
 
 static void
@@ -696,44 +702,85 @@ SetPossibleUnsafeConflict(SERIALIZABLEXACT *roXact,
 						  SERIALIZABLEXACT *activeXact)
 {
 	RWConflict	conflict;
+	bool		found;
 
 	Assert(roXact != activeXact);
 	Assert(SxactIsReadOnly(roXact));
 	Assert(!SxactIsReadOnly(activeXact));
 
-	conflict = (RWConflict)
-		SHMQueueNext(&RWConflictPool->availableList,
-					 &RWConflictPool->availableList,
-					 offsetof(RWConflictData, outLink));
-	if (!conflict)
-		ereport(ERROR,
+	conflict = (RWConflict)hash_search(roXact->possibleUnsafeConflictsTab,
+										&activeXact,
+										HASH_ENTER_NULL,
+										&found);
+	if (!found || conflict == NULL)
+	{
+		ereport(ERROR, 
 				(errcode(ERRCODE_OUT_OF_MEMORY),
-				 errmsg("not enough elements in RWConflictPool to record a potential read/write conflict"),
-				 errhint("You might need to run fewer transactions at a time or increase max_connections.")));
-
-	SHMQueueDelete(&conflict->outLink);
+				 errmsg("insert to possibleUnsafeConflicts hash table failed")));
+	}
+	conflict->sxactOut = activeXact;
+	conflict->sxactIn = roXact;
 
+	conflict = (RWConflict)hash_search(activeXact->possibleUnsafeConflictsTab,
+										&roXact,
+										HASH_ENTER_NULL,
+										&found);
+	if (!found || conflict == NULL)
+	{
+		ereport(ERROR, 
+				(errcode(ERRCODE_OUT_OF_MEMORY),
+				 errmsg("insert to possibleUnsafeConflicts hash table failed")));
+	}
 	conflict->sxactOut = activeXact;
 	conflict->sxactIn = roXact;
-	SHMQueueInsertBefore(&activeXact->possibleUnsafeConflicts,
-						 &conflict->outLink);
-	SHMQueueInsertBefore(&roXact->possibleUnsafeConflicts,
-						 &conflict->inLink);
 }
 
+/*
+ *	PossibleUnsafeConflicts are stored in a different hash table. Thus we need a new function
+ *	NOTE: the two functions below could be merged.
+ */
+
 static void
 ReleaseRWConflict(RWConflict conflict)
 {
-	SHMQueueDelete(&conflict->inLink);
-	SHMQueueDelete(&conflict->outLink);
-	SHMQueueInsertBefore(&RWConflictPool->availableList, &conflict->outLink);
+	bool found;
+
+	hash_search(conflict->sxactOut->outConflictsTab,
+				&conflict->sxactIn,
+				HASH_REMOVE,
+				&found);
+	Assert(found);
+
+	hash_search(conflict->sxactIn->inConflictsTab,
+				&conflict->sxactOut,
+				HASH_REMOVE,
+				&found);
+	Assert(found);
+}
+
+static void
+ReleaseUnsafeRWConflict(RWConflict conflict)
+{
+	bool		found;
+	
+	hash_search(conflict->sxactOut->possibleUnsafeConflictsTab,
+				&conflict->sxactIn,
+				HASH_REMOVE,
+				&found);
+	Assert(found);
+
+	hash_search(conflict->sxactIn->possibleUnsafeConflictsTab,
+				&conflict->sxactOut,
+				HASH_REMOVE,
+				&found);
+	Assert(found);
 }
 
 static void
 FlagSxactUnsafe(SERIALIZABLEXACT *sxact)
 {
-	RWConflict	conflict,
-				nextConflict;
+	RWConflict			conflict;
+	HASH_SEQ_STATUS		seqstat;
 
 	Assert(SxactIsReadOnly(sxact));
 	Assert(!SxactIsROSafe(sxact));
@@ -744,23 +791,13 @@ FlagSxactUnsafe(SERIALIZABLEXACT *sxact)
 	 * We know this isn't a safe snapshot, so we can stop looking for other
 	 * potential conflicts.
 	 */
-	conflict = (RWConflict)
-		SHMQueueNext(&sxact->possibleUnsafeConflicts,
-					 &sxact->possibleUnsafeConflicts,
-					 offsetof(RWConflictData, inLink));
-	while (conflict)
+	hash_seq_init(&seqstat, sxact->possibleUnsafeConflictsTab);
+	while ((conflict = (RWConflict)hash_seq_search(&seqstat))!=NULL)
 	{
-		nextConflict = (RWConflict)
-			SHMQueueNext(&sxact->possibleUnsafeConflicts,
-						 &conflict->inLink,
-						 offsetof(RWConflictData, inLink));
-
 		Assert(!SxactIsReadOnly(conflict->sxactOut));
 		Assert(sxact == conflict->sxactIn);
 
-		ReleaseRWConflict(conflict);
-
-		conflict = nextConflict;
+		ReleaseUnsafeRWConflict(conflict);
 	}
 }
 
@@ -1181,6 +1218,9 @@ InitPredicateLocks(void)
 	{
 		int			i;
 
+		/* 50 is enough for a hash table name */
+		const char	name[50];
+
 		SHMQueueInit(&PredXact->availableList);
 		SHMQueueInit(&PredXact->activeList);
 		PredXact->SxactGlobalXmin = InvalidTransactionId;
@@ -1194,21 +1234,52 @@ InitPredicateLocks(void)
 		PredXact->element = ShmemAlloc(requestSize);
 		/* Add all elements to available list, clean. */
 		memset(PredXact->element, 0, requestSize);
+
+		MemSet(&info, 0, sizeof(info));
+		info.keysize = sizeof(SERIALIZABLEXACT*);
+		info.entrysize = sizeof(RWConflictData);
+		info.num_partitions = NUM_PREDICATELOCK_PARTITIONS;
+
 		for (i = 0; i < max_table_size; i++)
 		{
 			SHMQueueInsertBefore(&(PredXact->availableList),
 								 &(PredXact->element[i].link));
+
+			snprintf((char*)name, 50, "PredXact inConflictsTab %d", i);
+			PredXact->element[i].sxact.inConflictsTab = ShmemInitHash(name, 
+																  SERIALIZABLEXACT_CONFLICT_HASHTAB_SIZE, 
+																  SERIALIZABLEXACT_CONFLICT_HASHTAB_SIZE, 
+																  &info, 
+																  HASH_ELEM | HASH_BLOBS | 
+																  HASH_PARTITION | HASH_FIXED_SIZE);
+
+			snprintf((char*)name, 50, "PredXact outConflictsTab %d", i);
+			PredXact->element[i].sxact.outConflictsTab = ShmemInitHash(name,
+																  SERIALIZABLEXACT_CONFLICT_HASHTAB_SIZE, 
+																  SERIALIZABLEXACT_CONFLICT_HASHTAB_SIZE, 
+																  &info, 
+																  HASH_ELEM | HASH_BLOBS |
+																  HASH_PARTITION | HASH_FIXED_SIZE); 
+
+			snprintf((char*)name, 50, "PredXact possibleUnsafeConflictsTab %d", i);
+			PredXact->element[i].sxact.possibleUnsafeConflictsTab = ShmemInitHash(name,
+																				   SERIALIZABLEXACT_CONFLICT_HASHTAB_SIZE, 
+																				   SERIALIZABLEXACT_CONFLICT_HASHTAB_SIZE, 
+																				   &info, 
+																				   HASH_ELEM | HASH_BLOBS |
+																				   HASH_PARTITION | HASH_FIXED_SIZE);
 		}
+
 		PredXact->OldCommittedSxact = CreatePredXact();
 		SetInvalidVirtualTransactionId(PredXact->OldCommittedSxact->vxid);
 		PredXact->OldCommittedSxact->prepareSeqNo = 0;
 		PredXact->OldCommittedSxact->commitSeqNo = 0;
 		PredXact->OldCommittedSxact->SeqNo.lastCommitBeforeSnapshot = 0;
-		SHMQueueInit(&PredXact->OldCommittedSxact->outConflicts);
-		SHMQueueInit(&PredXact->OldCommittedSxact->inConflicts);
+		//SHMQueueInit(&PredXact->OldCommittedSxact->outConflicts);
+		//SHMQueueInit(&PredXact->OldCommittedSxact->inConflicts);
 		SHMQueueInit(&PredXact->OldCommittedSxact->predicateLocks);
 		SHMQueueInit(&PredXact->OldCommittedSxact->finishedLink);
-		SHMQueueInit(&PredXact->OldCommittedSxact->possibleUnsafeConflicts);
+		//SHMQueueInit(&PredXact->OldCommittedSxact->possibleUnsafeConflicts);
 		PredXact->OldCommittedSxact->topXid = InvalidTransactionId;
 		PredXact->OldCommittedSxact->finishedBefore = InvalidTransactionId;
 		PredXact->OldCommittedSxact->xmin = InvalidTransactionId;
@@ -1246,26 +1317,6 @@ InitPredicateLocks(void)
 	 */
 	max_table_size *= 5;
 
-	RWConflictPool = ShmemInitStruct("RWConflictPool",
-									 RWConflictPoolHeaderDataSize,
-									 &found);
-	if (!found)
-	{
-		int			i;
-
-		SHMQueueInit(&RWConflictPool->availableList);
-		requestSize = mul_size((Size) max_table_size,
-							   RWConflictDataSize);
-		RWConflictPool->element = ShmemAlloc(requestSize);
-		/* Add all elements to available list, clean. */
-		memset(RWConflictPool->element, 0, requestSize);
-		for (i = 0; i < max_table_size; i++)
-		{
-			SHMQueueInsertBefore(&(RWConflictPool->availableList),
-								 &(RWConflictPool->element[i].outLink));
-		}
-	}
-
 	/*
 	 * Create or attach to the header for the list of finished serializable
 	 * transactions.
@@ -1320,13 +1371,23 @@ PredicateLockShmemSize(void)
 	size = add_size(size, mul_size((Size) max_table_size,
 								   PredXactListElementDataSize));
 
+	/* Hash table in Sxact 
+	 *
+	 * NOTE: It should be 3*max_table_size*hash_table_size. Because for each Sxact, there are
+	 		 3 HTAB: inConflictsTab, outConflictsTab, possibleUnsafeConflictsTab.
+	 *		 But I don't know why this setting will cause "out of memory". So I set it as 6.
+	 */
+	size = add_size(size, mul_size((Size) 6*max_table_size, 
+								   hash_estimate_size(SERIALIZABLEXACT_CONFLICT_HASHTAB_SIZE, 
+								   sizeof(RWConflict))));
+
 	/* transaction xid table */
 	size = add_size(size, hash_estimate_size(max_table_size,
 											 sizeof(SERIALIZABLEXID)));
 
 	/* rw-conflict pool */
 	max_table_size *= 5;
-	size = add_size(size, RWConflictPoolHeaderDataSize);
+
 	size = add_size(size, mul_size((Size) max_table_size,
 								   RWConflictDataSize));
 
@@ -1522,7 +1583,7 @@ GetSafeSnapshot(Snapshot origSnapshot)
 		 * them marked us as conflicted.
 		 */
 		MySerializableXact->flags |= SXACT_FLAG_DEFERRABLE_WAITING;
-		while (!(SHMQueueEmpty(&MySerializableXact->possibleUnsafeConflicts) ||
+		while (!(hash_table_empty(MySerializableXact->possibleUnsafeConflictsTab) || 
 				 SxactIsROUnsafe(MySerializableXact)))
 		{
 			LWLockRelease(SerializableXactHashLock);
@@ -1569,6 +1630,7 @@ GetSafeSnapshotBlockingPids(int blocked_pid, int *output, int output_size)
 {
 	int			num_written = 0;
 	SERIALIZABLEXACT *sxact;
+	HASH_SEQ_STATUS		seqstat;
 
 	LWLockAcquire(SerializableXactHashLock, LW_SHARED);
 
@@ -1585,18 +1647,11 @@ GetSafeSnapshotBlockingPids(int blocked_pid, int *output, int output_size)
 		RWConflict	possibleUnsafeConflict;
 
 		/* Traverse the list of possible unsafe conflicts collecting PIDs. */
-		possibleUnsafeConflict = (RWConflict)
-			SHMQueueNext(&sxact->possibleUnsafeConflicts,
-						 &sxact->possibleUnsafeConflicts,
-						 offsetof(RWConflictData, inLink));
 
-		while (possibleUnsafeConflict != NULL && num_written < output_size)
+		hash_seq_init(&seqstat, sxact->possibleUnsafeConflictsTab);
+		while ((possibleUnsafeConflict = hash_seq_search(&seqstat))!=NULL)
 		{
 			output[num_written++] = possibleUnsafeConflict->sxactOut->pid;
-			possibleUnsafeConflict = (RWConflict)
-				SHMQueueNext(&sxact->possibleUnsafeConflicts,
-							 &possibleUnsafeConflict->inLink,
-							 offsetof(RWConflictData, inLink));
 		}
 	}
 
@@ -1796,9 +1851,6 @@ GetSerializableTransactionSnapshotInt(Snapshot snapshot,
 	sxact->SeqNo.lastCommitBeforeSnapshot = PredXact->LastSxactCommitSeqNo;
 	sxact->prepareSeqNo = InvalidSerCommitSeqNo;
 	sxact->commitSeqNo = InvalidSerCommitSeqNo;
-	SHMQueueInit(&(sxact->outConflicts));
-	SHMQueueInit(&(sxact->inConflicts));
-	SHMQueueInit(&(sxact->possibleUnsafeConflicts));
 	sxact->topXid = GetTopTransactionIdIfAny();
 	sxact->finishedBefore = InvalidTransactionId;
 	sxact->xmin = snapshot->xmin;
@@ -3250,9 +3302,9 @@ ReleasePredicateLocks(bool isCommit)
 {
 	bool		needToClear;
 	RWConflict	conflict,
-				nextConflict,
 				possibleUnsafeConflict;
 	SERIALIZABLEXACT *roXact;
+	HASH_SEQ_STATUS seqstat;
 
 	/*
 	 * We can't trust XactReadOnly here, because a transaction which started
@@ -3361,23 +3413,15 @@ ReleasePredicateLocks(bool isCommit)
 		 * make us unsafe. Note that we use 'inLink' for the iteration as
 		 * opposed to 'outLink' for the r/w xacts.
 		 */
-		possibleUnsafeConflict = (RWConflict)
-			SHMQueueNext(&MySerializableXact->possibleUnsafeConflicts,
-						 &MySerializableXact->possibleUnsafeConflicts,
-						 offsetof(RWConflictData, inLink));
-		while (possibleUnsafeConflict)
-		{
-			nextConflict = (RWConflict)
-				SHMQueueNext(&MySerializableXact->possibleUnsafeConflicts,
-							 &possibleUnsafeConflict->inLink,
-							 offsetof(RWConflictData, inLink));
 
+		hash_seq_init(&seqstat, MySerializableXact->possibleUnsafeConflictsTab);
+		while ((possibleUnsafeConflict = hash_seq_search(&seqstat)) != NULL)
+
+		{
 			Assert(!SxactIsReadOnly(possibleUnsafeConflict->sxactOut));
 			Assert(MySerializableXact == possibleUnsafeConflict->sxactIn);
 
-			ReleaseRWConflict(possibleUnsafeConflict);
-
-			possibleUnsafeConflict = nextConflict;
+			ReleaseUnsafeRWConflict(possibleUnsafeConflict);
 		}
 	}
 
@@ -3400,17 +3444,9 @@ ReleasePredicateLocks(bool isCommit)
 	 * back clear them all.  Set SXACT_FLAG_CONFLICT_OUT if any point to
 	 * previously committed transactions.
 	 */
-	conflict = (RWConflict)
-		SHMQueueNext(&MySerializableXact->outConflicts,
-					 &MySerializableXact->outConflicts,
-					 offsetof(RWConflictData, outLink));
-	while (conflict)
+	hash_seq_init(&seqstat, MySerializableXact->outConflictsTab);
+	while((conflict = (RWConflict)hash_seq_search(&seqstat))!=NULL)
 	{
-		nextConflict = (RWConflict)
-			SHMQueueNext(&MySerializableXact->outConflicts,
-						 &conflict->outLink,
-						 offsetof(RWConflictData, outLink));
-
 		if (isCommit
 			&& !SxactIsReadOnly(MySerializableXact)
 			&& SxactIsCommitted(conflict->sxactIn))
@@ -3425,33 +3461,22 @@ ReleasePredicateLocks(bool isCommit)
 			|| SxactIsCommitted(conflict->sxactIn)
 			|| (conflict->sxactIn->SeqNo.lastCommitBeforeSnapshot >= PredXact->LastSxactCommitSeqNo))
 			ReleaseRWConflict(conflict);
-
-		conflict = nextConflict;
 	}
 
 	/*
 	 * Release all inConflicts from committed and read-only transactions. If
 	 * we're rolling back, clear them all.
 	 */
-	conflict = (RWConflict)
-		SHMQueueNext(&MySerializableXact->inConflicts,
-					 &MySerializableXact->inConflicts,
-					 offsetof(RWConflictData, inLink));
-	while (conflict)
+	hash_seq_init(&seqstat, MySerializableXact->inConflictsTab);
+	while((conflict = (RWConflict)hash_seq_search(&seqstat))!=NULL)
 	{
-		nextConflict = (RWConflict)
-			SHMQueueNext(&MySerializableXact->inConflicts,
-						 &conflict->inLink,
-						 offsetof(RWConflictData, inLink));
-
 		if (!isCommit
 			|| SxactIsCommitted(conflict->sxactOut)
 			|| SxactIsReadOnly(conflict->sxactOut))
 			ReleaseRWConflict(conflict);
-
-		conflict = nextConflict;
 	}
 
+
 	if (!topLevelIsDeclaredReadOnly)
 	{
 		/*
@@ -3460,17 +3485,10 @@ ReleasePredicateLocks(bool isCommit)
 		 * conflict out. If any are waiting DEFERRABLE transactions, wake them
 		 * up if they are known safe or known unsafe.
 		 */
-		possibleUnsafeConflict = (RWConflict)
-			SHMQueueNext(&MySerializableXact->possibleUnsafeConflicts,
-						 &MySerializableXact->possibleUnsafeConflicts,
-						 offsetof(RWConflictData, outLink));
-		while (possibleUnsafeConflict)
+		
+		hash_seq_init(&seqstat, MySerializableXact->possibleUnsafeConflictsTab);
+		while ((possibleUnsafeConflict = hash_seq_search(&seqstat))!=NULL)
 		{
-			nextConflict = (RWConflict)
-				SHMQueueNext(&MySerializableXact->possibleUnsafeConflicts,
-							 &possibleUnsafeConflict->outLink,
-							 offsetof(RWConflictData, outLink));
-
 			roXact = possibleUnsafeConflict->sxactIn;
 			Assert(MySerializableXact == possibleUnsafeConflict->sxactOut);
 			Assert(SxactIsReadOnly(roXact));
@@ -3490,14 +3508,14 @@ ReleasePredicateLocks(bool isCommit)
 			}
 			else
 			{
-				ReleaseRWConflict(possibleUnsafeConflict);
+				ReleaseUnsafeRWConflict(possibleUnsafeConflict);
 
 				/*
 				 * If we were the last possible conflict, flag it safe. The
 				 * transaction can now safely release its predicate locks (but
 				 * that transaction's backend has to do that itself).
 				 */
-				if (SHMQueueEmpty(&roXact->possibleUnsafeConflicts))
+				if (hash_table_empty(roXact->possibleUnsafeConflictsTab))
 					roXact->flags |= SXACT_FLAG_RO_SAFE;
 			}
 
@@ -3509,7 +3527,6 @@ ReleasePredicateLocks(bool isCommit)
 				(SxactIsROUnsafe(roXact) || SxactIsROSafe(roXact)))
 				ProcSendSignal(roXact->pid);
 
-			possibleUnsafeConflict = nextConflict;
 		}
 	}
 
@@ -3726,8 +3743,8 @@ ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial,
 {
 	PREDICATELOCK *predlock;
 	SERIALIZABLEXIDTAG sxidtag;
-	RWConflict	conflict,
-				nextConflict;
+	RWConflict	conflict;
+	HASH_SEQ_STATUS seqstat;
 
 	Assert(sxact != NULL);
 	Assert(SxactIsRolledBack(sxact) || SxactIsCommitted(sxact));
@@ -3823,41 +3840,25 @@ ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial,
 	sxidtag.xid = sxact->topXid;
 	LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
 
-	/* Release all outConflicts (unless 'partial' is true) */
+	/* Release all outConflictsTab (unless 'partial' is true) */
 	if (!partial)
 	{
-		conflict = (RWConflict)
-			SHMQueueNext(&sxact->outConflicts,
-						 &sxact->outConflicts,
-						 offsetof(RWConflictData, outLink));
-		while (conflict)
+		hash_seq_init(&seqstat, sxact->outConflictsTab);
+		while((conflict = (RWConflict)hash_seq_search(&seqstat))!=NULL)
 		{
-			nextConflict = (RWConflict)
-				SHMQueueNext(&sxact->outConflicts,
-							 &conflict->outLink,
-							 offsetof(RWConflictData, outLink));
 			if (summarize)
 				conflict->sxactIn->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN;
 			ReleaseRWConflict(conflict);
-			conflict = nextConflict;
 		}
 	}
 
-	/* Release all inConflicts. */
-	conflict = (RWConflict)
-		SHMQueueNext(&sxact->inConflicts,
-					 &sxact->inConflicts,
-					 offsetof(RWConflictData, inLink));
-	while (conflict)
+	/* Release all inConflictsTab. */
+	hash_seq_init(&seqstat, sxact->inConflictsTab);
+	while((conflict = (RWConflict)hash_seq_search(&seqstat))!=NULL)
 	{
-		nextConflict = (RWConflict)
-			SHMQueueNext(&sxact->inConflicts,
-						 &conflict->inLink,
-						 offsetof(RWConflictData, inLink));
 		if (summarize)
 			conflict->sxactOut->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT;
 		ReleaseRWConflict(conflict);
-		conflict = nextConflict;
 	}
 
 	/* Finally, get rid of the xid and the record of the transaction itself. */
@@ -4035,7 +4036,8 @@ CheckForSerializableConflictOut(bool visible, Relation relation,
 					  errhint("The transaction might succeed if retried.")));
 
 			if (SxactHasSummaryConflictIn(MySerializableXact)
-				|| !SHMQueueEmpty(&MySerializableXact->inConflicts))
+			//	|| !SHMQueueEmpty(&MySerializableXact->inConflicts))
+				|| !hash_table_empty(MySerializableXact->inConflictsTab))
 				ereport(ERROR,
 						(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
 						 errmsg("could not serialize access due to read/write dependencies among transactions"),
@@ -4520,6 +4522,7 @@ OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader,
 {
 	bool		failure;
 	RWConflict	conflict;
+	HASH_SEQ_STATUS seqstat;
 
 	Assert(LWLockHeldByMe(SerializableXactHashLock));
 
@@ -4567,29 +4570,24 @@ OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader,
 			conflict = NULL;
 		}
 		else
-			conflict = (RWConflict)
-				SHMQueueNext(&writer->outConflicts,
-							 &writer->outConflicts,
-							 offsetof(RWConflictData, outLink));
-		while (conflict)
 		{
-			SERIALIZABLEXACT *t2 = conflict->sxactIn;
-
-			if (SxactIsPrepared(t2)
-				&& (!SxactIsCommitted(reader)
-					|| t2->prepareSeqNo <= reader->commitSeqNo)
-				&& (!SxactIsCommitted(writer)
-					|| t2->prepareSeqNo <= writer->commitSeqNo)
-				&& (!SxactIsReadOnly(reader)
-			  || t2->prepareSeqNo <= reader->SeqNo.lastCommitBeforeSnapshot))
+			hash_seq_init(&seqstat, writer->outConflictsTab);
+			while ((conflict = hash_seq_search(&seqstat))!=NULL)
 			{
-				failure = true;
-				break;
+				SERIALIZABLEXACT *t2 = conflict->sxactIn;
+
+				if (SxactIsPrepared(t2)
+					&& (!SxactIsCommitted(reader)
+						|| t2->prepareSeqNo <= reader->commitSeqNo)
+					&& (!SxactIsCommitted(writer)
+						|| t2->prepareSeqNo <= writer->commitSeqNo)
+					&& (!SxactIsReadOnly(reader)
+				  || t2->prepareSeqNo <= reader->SeqNo.lastCommitBeforeSnapshot))
+				{
+					failure = true;
+					break;
+				}
 			}
-			conflict = (RWConflict)
-				SHMQueueNext(&writer->outConflicts,
-							 &conflict->outLink,
-							 offsetof(RWConflictData, outLink));
 		}
 	}
 
@@ -4614,27 +4612,22 @@ OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader,
 			conflict = NULL;
 		}
 		else
-			conflict = (RWConflict)
-				SHMQueueNext(&reader->inConflicts,
-							 &reader->inConflicts,
-							 offsetof(RWConflictData, inLink));
-		while (conflict)
 		{
-			SERIALIZABLEXACT *t0 = conflict->sxactOut;
-
-			if (!SxactIsDoomed(t0)
-				&& (!SxactIsCommitted(t0)
-					|| t0->commitSeqNo >= writer->prepareSeqNo)
-				&& (!SxactIsReadOnly(t0)
-			  || t0->SeqNo.lastCommitBeforeSnapshot >= writer->prepareSeqNo))
+			hash_seq_init(&seqstat, reader->inConflictsTab);
+			while((conflict = (RWConflict)hash_seq_search(&seqstat))!=NULL)
 			{
-				failure = true;
-				break;
+				SERIALIZABLEXACT *t0 = conflict->sxactOut;
+
+				if (!SxactIsDoomed(t0)
+					&& (!SxactIsCommitted(t0)
+						|| t0->commitSeqNo >= writer->prepareSeqNo)
+					&& (!SxactIsReadOnly(t0)
+				  || t0->SeqNo.lastCommitBeforeSnapshot >= writer->prepareSeqNo))
+				{
+					failure = true;
+					break;
+				}
 			}
-			conflict = (RWConflict)
-				SHMQueueNext(&reader->inConflicts,
-							 &conflict->inLink,
-							 offsetof(RWConflictData, inLink));
 		}
 	}
 
@@ -4693,6 +4686,7 @@ void
 PreCommit_CheckForSerializationFailure(void)
 {
 	RWConflict	nearConflict;
+	HASH_SEQ_STATUS nearseqstat;
 
 	if (MySerializableXact == InvalidSerializableXact)
 		return;
@@ -4712,22 +4706,18 @@ PreCommit_CheckForSerializationFailure(void)
 				 errhint("The transaction might succeed if retried.")));
 	}
 
-	nearConflict = (RWConflict)
-		SHMQueueNext(&MySerializableXact->inConflicts,
-					 &MySerializableXact->inConflicts,
-					 offsetof(RWConflictData, inLink));
-	while (nearConflict)
+	hash_seq_init(&nearseqstat, MySerializableXact->inConflictsTab);
+	while((nearConflict = hash_seq_search(&nearseqstat))!=NULL)
 	{
 		if (!SxactIsCommitted(nearConflict->sxactOut)
 			&& !SxactIsDoomed(nearConflict->sxactOut))
 		{
-			RWConflict	farConflict;
+			RWConflict farConflict;
+			HASH_SEQ_STATUS farseqstat;
+			
+			hash_seq_init(&farseqstat, nearConflict->sxactOut->inConflictsTab);
 
-			farConflict = (RWConflict)
-				SHMQueueNext(&nearConflict->sxactOut->inConflicts,
-							 &nearConflict->sxactOut->inConflicts,
-							 offsetof(RWConflictData, inLink));
-			while (farConflict)
+			while((farConflict = hash_seq_search(&farseqstat))!=NULL)
 			{
 				if (farConflict->sxactOut == MySerializableXact
 					|| (!SxactIsCommitted(farConflict->sxactOut)
@@ -4752,17 +4742,8 @@ PreCommit_CheckForSerializationFailure(void)
 					nearConflict->sxactOut->flags |= SXACT_FLAG_DOOMED;
 					break;
 				}
-				farConflict = (RWConflict)
-					SHMQueueNext(&nearConflict->sxactOut->inConflicts,
-								 &farConflict->inLink,
-								 offsetof(RWConflictData, inLink));
 			}
 		}
-
-		nearConflict = (RWConflict)
-			SHMQueueNext(&MySerializableXact->inConflicts,
-						 &nearConflict->inLink,
-						 offsetof(RWConflictData, inLink));
 	}
 
 	MySerializableXact->prepareSeqNo = ++(PredXact->LastSxactCommitSeqNo);
@@ -4948,7 +4929,6 @@ predicatelock_twophase_recover(TransactionId xid, uint16 info,
 		 * recovered xact started are still active, except possibly other
 		 * prepared xacts and we don't care whether those are RO_SAFE or not.
 		 */
-		SHMQueueInit(&(sxact->possibleUnsafeConflicts));
 
 		SHMQueueInit(&(sxact->predicateLocks));
 		SHMQueueElemInit(&(sxact->finishedLink));
@@ -4969,8 +4949,6 @@ predicatelock_twophase_recover(TransactionId xid, uint16 info,
 		 * we'll conservatively assume that it had both a conflict in and a
 		 * conflict out, and represent that with the summary conflict flags.
 		 */
-		SHMQueueInit(&(sxact->outConflicts));
-		SHMQueueInit(&(sxact->inConflicts));
 		sxact->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN;
 		sxact->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT;
 
diff --git a/src/include/storage/predicate_internals.h b/src/include/storage/predicate_internals.h
index 3cb0ab9..948827d 100644
--- a/src/include/storage/predicate_internals.h
+++ b/src/include/storage/predicate_internals.h
@@ -38,6 +38,12 @@ typedef uint64 SerCommitSeqNo;
 #define FirstNormalSerCommitSeqNo	((SerCommitSeqNo) 2)
 
 /*
+ * Hash table size in SERIALIZABLEXACT 
+ */
+#define SERIALIZABLEXACT_CONFLICT_HASHTAB_SIZE 200
+
+
+/*
  * The SERIALIZABLEXACT struct contains information needed for each
  * serializable database transaction to support SSI techniques.
  *
@@ -83,10 +89,10 @@ typedef struct SERIALIZABLEXACT
 		SerCommitSeqNo lastCommitBeforeSnapshot;		/* when not committed or
 														 * no conflict out */
 	}			SeqNo;
-	SHM_QUEUE	outConflicts;	/* list of write transactions whose data we
-								 * couldn't read. */
-	SHM_QUEUE	inConflicts;	/* list of read transactions which couldn't
-								 * see our write. */
+
+	HTAB*		outConflictsTab;	/* Table of write transactions whose data we couldn't read  */
+	HTAB*		inConflictsTab;		/* Table of read transactions which couldn't see our write. */
+
 	SHM_QUEUE	predicateLocks; /* list of associated PREDICATELOCK objects */
 	SHM_QUEUE	finishedLink;	/* list link in
 								 * FinishedSerializableTransactions */
@@ -95,7 +101,7 @@ typedef struct SERIALIZABLEXACT
 	 * for r/o transactions: list of concurrent r/w transactions that we could
 	 * potentially have conflicts with, and vice versa for r/w transactions
 	 */
-	SHM_QUEUE	possibleUnsafeConflicts;
+	HTAB*		possibleUnsafeConflictsTab;
 
 	TransactionId topXid;		/* top level xid for the transaction, if one
 								 * exists; else invalid */
@@ -205,18 +211,6 @@ typedef struct RWConflictData *RWConflict;
 #define RWConflictDataSize \
 		((Size)MAXALIGN(sizeof(RWConflictData)))
 
-typedef struct RWConflictPoolHeaderData
-{
-	SHM_QUEUE	availableList;
-	RWConflict	element;
-}	RWConflictPoolHeaderData;
-
-typedef struct RWConflictPoolHeaderData *RWConflictPoolHeader;
-
-#define RWConflictPoolHeaderDataSize \
-		((Size)MAXALIGN(sizeof(RWConflictPoolHeaderData)))
-
-
 /*
  * The SERIALIZABLEXIDTAG struct identifies an xid assigned to a serializable
  * transaction or any of its subtransactions.