diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 0555b02a8d..d15c44b5b7 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -338,9 +338,9 @@ static void DisplayXidCache(void);
 static void KnownAssignedXidsCompress(bool force);
 static void KnownAssignedXidsAdd(TransactionId from_xid, TransactionId to_xid,
 								 bool exclusive_lock);
-static bool KnownAssignedXidsSearch(TransactionId xid, bool remove);
+static int KnownAssignedXidsSearch(TransactionId xid, bool remove, int start);
 static bool KnownAssignedXidExists(TransactionId xid);
-static void KnownAssignedXidsRemove(TransactionId xid);
+static int KnownAssignedXidsRemove(TransactionId xid, int start);
 static void KnownAssignedXidsRemoveTree(TransactionId xid, int nsubxids,
 										TransactionId *subxids);
 static void KnownAssignedXidsRemovePreceding(TransactionId xid);
@@ -4771,6 +4771,9 @@ KnownAssignedXidsAdd(TransactionId from_xid, TransactionId to_xid,
 	}
 }
 
+#define KAX_INVALID	-1
+#define KAX_START	KAX_INVALID
+
 /*
  * KnownAssignedXidsSearch
  *
@@ -4780,21 +4783,30 @@ KnownAssignedXidsAdd(TransactionId from_xid, TransactionId to_xid,
  * Caller must hold ProcArrayLock in shared or exclusive mode.
  * Exclusive lock must be held for remove = true.
  */
-static bool
-KnownAssignedXidsSearch(TransactionId xid, bool remove)
+static int
+KnownAssignedXidsSearch(TransactionId xid, bool remove, int start)
 {
 	ProcArrayStruct *pArray = procArray;
 	int			first,
 				last;
 	int			head;
 	int			tail;
-	int			result_index = -1;
+	int			result_index = KAX_INVALID;
 
 	if (remove)
 	{
 		/* we hold ProcArrayLock exclusively, so no need for spinlock */
-		tail = pArray->tailKnownAssignedXids;
 		head = pArray->headKnownAssignedXids;
+
+		/*
+		 * Start at the tail, or if we are removing a set of sorted
+		 * xids, we can set the tail to the location of previous removal,
+		 * reducing search time when N is large.
+		 */
+		if (start == KAX_START)
+			tail = pArray->tailKnownAssignedXids;
+		else
+			tail = start;
 	}
 	else
 	{
@@ -4831,10 +4843,10 @@ KnownAssignedXidsSearch(TransactionId xid, bool remove)
 	}
 
 	if (result_index < 0)
-		return false;			/* not in array */
+		return KAX_INVALID;			/* not in array */
 
 	if (!KnownAssignedXidsValid[result_index])
-		return false;			/* in array, but invalid */
+		return KAX_INVALID;			/* in array, but invalid */
 
 	if (remove)
 	{
@@ -4865,7 +4877,7 @@ KnownAssignedXidsSearch(TransactionId xid, bool remove)
 		}
 	}
 
-	return true;
+	return result_index;
 }
 
 /*
@@ -4878,16 +4890,18 @@ KnownAssignedXidExists(TransactionId xid)
 {
 	Assert(TransactionIdIsValid(xid));
 
-	return KnownAssignedXidsSearch(xid, false);
+	return KnownAssignedXidsSearch(xid, false, KAX_START) == KAX_INVALID ? false : true;
 }
 
 /*
  * Remove the specified XID from KnownAssignedXids[].
  *
  * Caller must hold ProcArrayLock in exclusive mode.
+ *
+ * Returns the array offset of the removed element, or KAX_INVALID if not present.
  */
-static void
-KnownAssignedXidsRemove(TransactionId xid)
+static int
+KnownAssignedXidsRemove(TransactionId xid, int start)
 {
 	Assert(TransactionIdIsValid(xid));
 
@@ -4903,7 +4917,7 @@ KnownAssignedXidsRemove(TransactionId xid)
 	 * actual errors, but it would be complicated and probably not worth it.
 	 * So, just ignore the search result.
 	 */
-	(void) KnownAssignedXidsSearch(xid, true);
+	return KnownAssignedXidsSearch(xid, true, start);
 }
 
 /*
@@ -4911,18 +4925,23 @@ KnownAssignedXidsRemove(TransactionId xid)
  *		Remove xid (if it's not InvalidTransactionId) and all the subxids.
  *
  * Caller must hold ProcArrayLock in exclusive mode.
+ *
+ * Since the xid and subxids are sorted, we can chain them together so
+ * we start searching for next xid at the point where we removed the previous
+ * xid in the tree. First search starts at KAX_START.
  */
 static void
 KnownAssignedXidsRemoveTree(TransactionId xid, int nsubxids,
 							TransactionId *subxids)
 {
 	int			i;
+	int			start = KAX_START;
 
 	if (TransactionIdIsValid(xid))
-		KnownAssignedXidsRemove(xid);
+		start = KnownAssignedXidsRemove(xid, start);
 
 	for (i = 0; i < nsubxids; i++)
-		KnownAssignedXidsRemove(subxids[i]);
+		start = KnownAssignedXidsRemove(subxids[i], start);
 
 	/* Opportunistically compress the array */
 	KnownAssignedXidsCompress(false);