diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 599874e..c9da8ed 100644
*** a/src/backend/tcop/postgres.c
--- b/src/backend/tcop/postgres.c
*************** exec_parse_message(const char *query_str
*** 1352,1357 ****
--- 1352,1358 ----
  		/* Done with the snapshot used for parsing */
  		if (snapshot_set)
  			PopActiveSnapshot();
+ 		InvalidateCatalogSnapshot();
  	}
  	else
  	{
*************** exec_bind_message(StringInfo input_messa
*** 1778,1783 ****
--- 1779,1785 ----
  	/* Done with the snapshot used for parameter I/O and parsing/planning */
  	if (snapshot_set)
  		PopActiveSnapshot();
+ 	InvalidateCatalogSnapshot();
  
  	/*
  	 * And we're ready to start portal execution.
*************** exec_execute_message(const char *portal_
*** 2000,2005 ****
--- 2002,2012 ----
  			 * those that start or end a transaction block.
  			 */
  			CommandCounterIncrement();
+ 
+ 			/*
+ 			 * Flush catalog snapshot after every query, too.
+ 			 */
+ 			InvalidateCatalogSnapshot();
  		}
  
  		/* Send appropriate CommandComplete to client */
*************** finish_xact_command(void)
*** 2456,2461 ****
--- 2463,2471 ----
  
  		CommitTransactionCommand();
  
+ 		/* Flush catalog snapshot if any */
+ 		InvalidateCatalogSnapshot();
+ 
  #ifdef MEMORY_CONTEXT_CHECKING
  		/* Check all memory contexts that weren't freed during commit */
  		/* (those that were, were checked before being deleted) */
*************** PostgresMain(int argc, char *argv[],
*** 3871,3876 ****
--- 3881,3888 ----
  		 */
  		AbortCurrentTransaction();
  
+ 		InvalidateCatalogSnapshot();
+ 
  		if (am_walsender)
  			WalSndErrorCleanup();
  
diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c
index 1ec9f70..842e135 100644
*** a/src/backend/utils/time/snapmgr.c
--- b/src/backend/utils/time/snapmgr.c
*************** GetTransactionSnapshot(void)
*** 316,321 ****
--- 316,327 ----
  	/* First call in transaction? */
  	if (!FirstSnapshotSet)
  	{
+ 		/*
+ 		 * Don't allow catalog snapshot to be older than xact snapshot.  Must
+ 		 * do this first to allow the empty-heap Assert to succeed.
+ 		 */
+ 		InvalidateCatalogSnapshot();
+ 
  		Assert(pairingheap_is_empty(&RegisteredSnapshots));
  		Assert(FirstXactSnapshot == NULL);
  
*************** GetTransactionSnapshot(void)
*** 347,355 ****
  		else
  			CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData);
  
- 		/* Don't allow catalog snapshot to be older than xact snapshot. */
- 		CatalogSnapshotStale = true;
- 
  		FirstSnapshotSet = true;
  		return CurrentSnapshot;
  	}
--- 353,358 ----
*************** GetTransactionSnapshot(void)
*** 358,364 ****
  		return CurrentSnapshot;
  
  	/* Don't allow catalog snapshot to be older than xact snapshot. */
! 	CatalogSnapshotStale = true;
  
  	CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData);
  
--- 361,367 ----
  		return CurrentSnapshot;
  
  	/* Don't allow catalog snapshot to be older than xact snapshot. */
! 	InvalidateCatalogSnapshot();
  
  	CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData);
  
*************** GetNonHistoricCatalogSnapshot(Oid relid)
*** 465,471 ****
  	 */
  	if (!CatalogSnapshotStale && !RelationInvalidatesSnapshotsOnly(relid) &&
  		!RelationHasSysCache(relid))
! 		CatalogSnapshotStale = true;
  
  	if (CatalogSnapshotStale)
  	{
--- 468,474 ----
  	 */
  	if (!CatalogSnapshotStale && !RelationInvalidatesSnapshotsOnly(relid) &&
  		!RelationHasSysCache(relid))
! 		InvalidateCatalogSnapshot();
  
  	if (CatalogSnapshotStale)
  	{
*************** GetNonHistoricCatalogSnapshot(Oid relid)
*** 473,478 ****
--- 476,491 ----
  		CatalogSnapshot = GetSnapshotData(&CatalogSnapshotData);
  
  		/*
+ 		 * Make sure the catalog snapshot will be accounted for in decisions
+ 		 * about advancing PGXACT->xmin.  We could apply RegisterSnapshot, but
+ 		 * that would result in making a physical copy, which is overkill; and
+ 		 * it would also create a dependency on some resource owner.  Instead
+ 		 * just shove the CatalogSnapshot into the pairing heap manually.
+ 		 * This has to be reversed in InvalidateCatalogSnapshot, of course.
+ 		 */
+ 		pairingheap_add(&RegisteredSnapshots, &CatalogSnapshot->ph_node);
+ 
+ 		/*
  		 * Mark new snapshost as valid.  We must do this last, in case an
  		 * ERROR occurs inside GetSnapshotData().
  		 */
*************** GetNonHistoricCatalogSnapshot(Oid relid)
*** 492,498 ****
  void
  InvalidateCatalogSnapshot(void)
  {
! 	CatalogSnapshotStale = true;
  }
  
  /*
--- 505,516 ----
  void
  InvalidateCatalogSnapshot(void)
  {
! 	if (!CatalogSnapshotStale)
! 	{
! 		CatalogSnapshotStale = true;
! 		pairingheap_remove(&RegisteredSnapshots, &CatalogSnapshot->ph_node);
! 		SnapshotResetXmin();
! 	}
  }
  
  /*
*************** SnapshotResetXmin(void)
*** 930,935 ****
--- 948,954 ----
  
  	if (pairingheap_is_empty(&RegisteredSnapshots))
  	{
+ 		Assert(CatalogSnapshotStale);
  		MyPgXact->xmin = InvalidTransactionId;
  		return;
  	}
*************** AtEOXact_Snapshot(bool isCommit)
*** 1058,1063 ****
--- 1077,1085 ----
  		exportedSnapshots = NIL;
  	}
  
+ 	/* Drop catalog snapshot if any */
+ 	InvalidateCatalogSnapshot();
+ 
  	/* On commit, complain about leftover snapshots */
  	if (isCommit)
  	{