1 files changed, 16 insertions, 1 deletions
diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c
index 2968c7f7b7d..dca1bc8afca 100644
--- a/src/backend/utils/time/snapmgr.c
+++ b/src/backend/utils/time/snapmgr.c
@@ -679,9 +679,24 @@ FreeSnapshot(Snapshot snapshot)
 void
 PushActiveSnapshot(Snapshot snap)
 {
+	PushActiveSnapshotWithLevel(snap, GetCurrentTransactionNestLevel());
+}
+
+/*
+ * PushActiveSnapshotWithLevel
+ *		Set the given snapshot as the current active snapshot
+ *
+ * Same as PushActiveSnapshot except that caller can specify the
+ * transaction nesting level that "owns" the snapshot.  This level
+ * must not be deeper than the current top of the snapshot stack.
+ */
+void
+PushActiveSnapshotWithLevel(Snapshot snap, int snap_level)
+{
 	ActiveSnapshotElt *newactive;
 
 	Assert(snap != InvalidSnapshot);
+	Assert(ActiveSnapshot == NULL || snap_level >= ActiveSnapshot->as_level);
 
 	newactive = MemoryContextAlloc(TopTransactionContext, sizeof(ActiveSnapshotElt));
 
@@ -695,7 +710,7 @@ PushActiveSnapshot(Snapshot snap)
 		newactive->as_snap = snap;
 
 	newactive->as_next = ActiveSnapshot;
-	newactive->as_level = GetCurrentTransactionNestLevel();
+	newactive->as_level = snap_level;
 
 	newactive->as_snap->active_count++;