diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 3447481b16..fd600944b6 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -109,6 +109,7 @@ static PGXACT *allPgXact;
  */
 static TransactionId *KnownAssignedXids;
 static bool *KnownAssignedXidsValid;
+static pg_atomic_uint32 *KnownAssignedXidsNext;
 static TransactionId latestObservedXid = InvalidTransactionId;
 
 /*
@@ -225,6 +226,7 @@ void
 CreateSharedProcArray(void)
 {
 	bool		found;
+	int			i;
 
 	/* Create or attach to the ProcArray shared structure */
 	procArray = (ProcArrayStruct *)
@@ -266,6 +268,12 @@ CreateSharedProcArray(void)
 			ShmemInitStruct("KnownAssignedXidsValid",
 							mul_size(sizeof(bool), TOTAL_MAX_CACHED_SUBXIDS),
 							&found);
+		KnownAssignedXidsNext = (pg_atomic_uint32 *)
+				ShmemInitStruct("KnownAssignedXidsNext",
+								mul_size(sizeof(pg_atomic_uint32), TOTAL_MAX_CACHED_SUBXIDS),
+								&found);
+		for (i = 0; i < TOTAL_MAX_CACHED_SUBXIDS; i++)
+			pg_atomic_init_u32(&KnownAssignedXidsNext[i], 1);
 	}
 }
 
@@ -3558,12 +3566,13 @@ KnownAssignedXidsCompress(bool force)
 	 * re-aligning data to 0th element.
 	 */
 	compress_index = 0;
-	for (i = tail; i < head; i++)
+	for (i = tail; i < head; i += pg_atomic_read_u32(&KnownAssignedXidsNext[i]))
 	{
 		if (KnownAssignedXidsValid[i])
 		{
 			KnownAssignedXids[compress_index] = KnownAssignedXids[i];
 			KnownAssignedXidsValid[compress_index] = true;
+			pg_atomic_write_u32(&KnownAssignedXidsNext[compress_index], 1);
 			compress_index++;
 		}
 	}
@@ -3666,6 +3675,7 @@ KnownAssignedXidsAdd(TransactionId from_xid, TransactionId to_xid,
 	{
 		KnownAssignedXids[head] = next_xid;
 		KnownAssignedXidsValid[head] = true;
+		pg_atomic_write_u32(&KnownAssignedXidsNext[head], 1);
 		TransactionIdAdvance(next_xid);
 		head++;
 	}
@@ -3881,7 +3891,7 @@ KnownAssignedXidsRemovePreceding(TransactionId removeXid)
 	tail = pArray->tailKnownAssignedXids;
 	head = pArray->headKnownAssignedXids;
 
-	for (i = tail; i < head; i++)
+	for (i = tail; i < head; i += pg_atomic_read_u32(&KnownAssignedXidsNext[i]))
 	{
 		if (KnownAssignedXidsValid[i])
 		{
@@ -3904,7 +3914,7 @@ KnownAssignedXidsRemovePreceding(TransactionId removeXid)
 	/*
 	 * Advance the tail pointer if we've marked the tail item invalid.
 	 */
-	for (i = tail; i < head; i++)
+	for (i = tail; i < head; i += pg_atomic_read_u32(&KnownAssignedXidsNext[i]))
 	{
 		if (KnownAssignedXidsValid[i])
 			break;
@@ -3954,7 +3964,8 @@ KnownAssignedXidsGetAndSetXmin(TransactionId *xarray, TransactionId *xmin,
 	int			count = 0;
 	int			head,
 				tail;
-	int			i;
+	int			i,
+				prev;
 
 	/*
 	 * Fetch head just once, since it may change while we loop. We can stop
@@ -3968,9 +3979,10 @@ KnownAssignedXidsGetAndSetXmin(TransactionId *xarray, TransactionId *xmin,
 	SpinLockAcquire(&procArray->known_assigned_xids_lck);
 	tail = procArray->tailKnownAssignedXids;
 	head = procArray->headKnownAssignedXids;
+	prev = tail;
 	SpinLockRelease(&procArray->known_assigned_xids_lck);
 
-	for (i = tail; i < head; i++)
+	for (i = tail; i < head; i += pg_atomic_read_u32(&KnownAssignedXidsNext[i]))
 	{
 		/* Skip any gaps in the array */
 		if (KnownAssignedXidsValid[i])
@@ -3993,6 +4005,14 @@ KnownAssignedXidsGetAndSetXmin(TransactionId *xarray, TransactionId *xmin,
 				TransactionIdFollowsOrEquals(knownXid, xmax))
 				break;
 
+			if (prev != i)
+			{
+				uint32 offset = i - prev;
+				if (pg_atomic_read_u32(&KnownAssignedXidsNext[prev]) != offset)
+					pg_atomic_write_u32(&KnownAssignedXidsNext[prev], offset);
+				prev = i;
+			}
+
 			/* Add knownXid into output array */
 			xarray[count++] = knownXid;
 		}
@@ -4020,7 +4040,7 @@ KnownAssignedXidsGetOldestXmin(void)
 	head = procArray->headKnownAssignedXids;
 	SpinLockRelease(&procArray->known_assigned_xids_lck);
 
-	for (i = tail; i < head; i++)
+	for (i = tail; i < head; i += pg_atomic_read_u32(&KnownAssignedXidsNext[i]))
 	{
 		/* Skip any gaps in the array */
 		if (KnownAssignedXidsValid[i])
@@ -4055,7 +4075,7 @@ KnownAssignedXidsDisplay(int trace_level)
 
 	initStringInfo(&buf);
 
-	for (i = tail; i < head; i++)
+	for (i = tail; i < head; i += pg_atomic_read_u32(&KnownAssignedXidsNext[i]))
 	{
 		if (KnownAssignedXidsValid[i])
 		{