Offer triggers on foreign tables.

This covers all the SQL-standard trigger types supported for regular
tables; it does not cover constraint triggers.  The approach for
acquiring the old row mirrors that for view INSTEAD OF triggers.  For
AFTER ROW triggers, we spool the foreign tuples to a tuplestore.

This changes the FDW API contract; when deciding which columns to
populate in the slot returned from data modification callbacks, writable
FDWs will need to check for AFTER ROW triggers in addition to checking
for a RETURNING clause.

In support of the feature addition, refactor the TriggerFlags bits and
the assembly of old tuples in ModifyTable.

Ronan Dunklau, reviewed by KaiGai Kohei; some additional hacking by me.

1 files changed, 340 insertions, 83 deletions

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index 3e92a7c29e5..5f1ccf02c27 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -56,6 +56,7 @@
 #include "utils/snapmgr.h"
 #include "utils/syscache.h"
 #include "utils/tqual.h"
+#include "utils/tuplestore.h"
 
 
 /* GUC variables */
@@ -195,6 +196,30 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 							RelationGetRelationName(rel)),
 					 errdetail("Views cannot have TRUNCATE triggers.")));
 	}
+	else if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
+	{
+		if (stmt->timing != TRIGGER_TYPE_BEFORE &&
+			stmt->timing != TRIGGER_TYPE_AFTER)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("\"%s\" is a foreign table",
+							RelationGetRelationName(rel)),
+			  errdetail("Foreign tables cannot have INSTEAD OF triggers.")));
+
+		if (TRIGGER_FOR_TRUNCATE(stmt->events))
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("\"%s\" is a foreign table",
+							RelationGetRelationName(rel)),
+				errdetail("Foreign tables cannot have TRUNCATE triggers.")));
+
+		if (stmt->isconstraint)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("\"%s\" is a foreign table",
+							RelationGetRelationName(rel)),
+			  errdetail("Foreign tables cannot have constraint triggers.")));
+	}
 	else
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
@@ -1080,10 +1105,11 @@ RemoveTriggerById(Oid trigOid)
 	rel = heap_open(relid, AccessExclusiveLock);
 
 	if (rel->rd_rel->relkind != RELKIND_RELATION &&
-		rel->rd_rel->relkind != RELKIND_VIEW)
+		rel->rd_rel->relkind != RELKIND_VIEW &&
+		rel->rd_rel->relkind != RELKIND_FOREIGN_TABLE)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is not a table or view",
+				 errmsg("\"%s\" is not a table, view, or foreign table",
 						RelationGetRelationName(rel))));
 
 	if (!allowSystemTableMods && IsSystemRelation(rel))
@@ -1184,10 +1210,12 @@ RangeVarCallbackForRenameTrigger(const RangeVar *rv, Oid relid, Oid oldrelid,
 	form = (Form_pg_class) GETSTRUCT(tuple);
 
 	/* only tables and views can have triggers */
-	if (form->relkind != RELKIND_RELATION && form->relkind != RELKIND_VIEW)
+	if (form->relkind != RELKIND_RELATION && form->relkind != RELKIND_VIEW &&
+		form->relkind != RELKIND_FOREIGN_TABLE)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is not a table or view", rv->relname)));
+				 errmsg("\"%s\" is not a table, view, or foreign table",
+						rv->relname)));
 
 	/* you must own the table to rename one of its triggers */
 	if (!pg_class_ownercheck(relid, GetUserId()))
@@ -2164,7 +2192,8 @@ ExecASDeleteTriggers(EState *estate, ResultRelInfo *relinfo)
 bool
 ExecBRDeleteTriggers(EState *estate, EPQState *epqstate,
 					 ResultRelInfo *relinfo,
-					 ItemPointer tupleid)
+					 ItemPointer tupleid,
+					 HeapTuple fdw_trigtuple)
 {
 	TriggerDesc *trigdesc = relinfo->ri_TrigDesc;
 	bool		result = true;
@@ -2174,10 +2203,16 @@ ExecBRDeleteTriggers(EState *estate, EPQState *epqstate,
 	TupleTableSlot *newSlot;
 	int			i;
 
-	trigtuple = GetTupleForTrigger(estate, epqstate, relinfo, tupleid,
-								   LockTupleExclusive, &newSlot);
-	if (trigtuple == NULL)
-		return false;
+	Assert(HeapTupleIsValid(fdw_trigtuple) ^ ItemPointerIsValid(tupleid));
+	if (fdw_trigtuple == NULL)
+	{
+		trigtuple = GetTupleForTrigger(estate, epqstate, relinfo, tupleid,
+									   LockTupleExclusive, &newSlot);
+		if (trigtuple == NULL)
+			return false;
+	}
+	else
+		trigtuple = fdw_trigtuple;
 
 	LocTriggerData.type = T_TriggerData;
 	LocTriggerData.tg_event = TRIGGER_EVENT_DELETE |
@@ -2215,29 +2250,38 @@ ExecBRDeleteTriggers(EState *estate, EPQState *epqstate,
 		if (newtuple != trigtuple)
 			heap_freetuple(newtuple);
 	}
-	heap_freetuple(trigtuple);
+	if (trigtuple != fdw_trigtuple)
+		heap_freetuple(trigtuple);
 
 	return result;
 }
 
 void
 ExecARDeleteTriggers(EState *estate, ResultRelInfo *relinfo,
-					 ItemPointer tupleid)
+					 ItemPointer tupleid,
+					 HeapTuple fdw_trigtuple)
 {
 	TriggerDesc *trigdesc = relinfo->ri_TrigDesc;
 
 	if (trigdesc && trigdesc->trig_delete_after_row)
 	{
-		HeapTuple	trigtuple = GetTupleForTrigger(estate,
-												   NULL,
-												   relinfo,
-												   tupleid,
-												   LockTupleExclusive,
-												   NULL);
+		HeapTuple	trigtuple;
+
+		Assert(HeapTupleIsValid(fdw_trigtuple) ^ ItemPointerIsValid(tupleid));
+		if (fdw_trigtuple == NULL)
+			trigtuple = GetTupleForTrigger(estate,
+										   NULL,
+										   relinfo,
+										   tupleid,
+										   LockTupleExclusive,
+										   NULL);
+		else
+			trigtuple = fdw_trigtuple;
 
 		AfterTriggerSaveEvent(estate, relinfo, TRIGGER_EVENT_DELETE,
 							  true, trigtuple, NULL, NIL, NULL);
-		heap_freetuple(trigtuple);
+		if (trigtuple != fdw_trigtuple)
+			heap_freetuple(trigtuple);
 	}
 }
 
@@ -2353,7 +2397,9 @@ ExecASUpdateTriggers(EState *estate, ResultRelInfo *relinfo)
 TupleTableSlot *
 ExecBRUpdateTriggers(EState *estate, EPQState *epqstate,
 					 ResultRelInfo *relinfo,
-					 ItemPointer tupleid, TupleTableSlot *slot)
+					 ItemPointer tupleid,
+					 HeapTuple fdw_trigtuple,
+					 TupleTableSlot *slot)
 {
 	TriggerDesc *trigdesc = relinfo->ri_TrigDesc;
 	HeapTuple	slottuple = ExecMaterializeSlot(slot);
@@ -2380,11 +2426,20 @@ ExecBRUpdateTriggers(EState *estate, EPQState *epqstate,
 	else
 		lockmode = LockTupleNoKeyExclusive;
 
-	/* get a copy of the on-disk tuple we are planning to update */
-	trigtuple = GetTupleForTrigger(estate, epqstate, relinfo, tupleid,
-								   lockmode, &newSlot);
-	if (trigtuple == NULL)
-		return NULL;			/* cancel the update action */
+	Assert(HeapTupleIsValid(fdw_trigtuple) ^ ItemPointerIsValid(tupleid));
+	if (fdw_trigtuple == NULL)
+	{
+		/* get a copy of the on-disk tuple we are planning to update */
+		trigtuple = GetTupleForTrigger(estate, epqstate, relinfo, tupleid,
+									   lockmode, &newSlot);
+		if (trigtuple == NULL)
+			return NULL;		/* cancel the update action */
+	}
+	else
+	{
+		trigtuple = fdw_trigtuple;
+		newSlot = NULL;
+	}
 
 	/*
 	 * In READ COMMITTED isolation level it's possible that target tuple was
@@ -2437,11 +2492,13 @@ ExecBRUpdateTriggers(EState *estate, EPQState *epqstate,
 			heap_freetuple(oldtuple);
 		if (newtuple == NULL)
 		{
-			heap_freetuple(trigtuple);
+			if (trigtuple != fdw_trigtuple)
+				heap_freetuple(trigtuple);
 			return NULL;		/* "do nothing" */
 		}
 	}
-	heap_freetuple(trigtuple);
+	if (trigtuple != fdw_trigtuple)
+		heap_freetuple(trigtuple);
 
 	if (newtuple != slottuple)
 	{
@@ -2464,24 +2521,33 @@ ExecBRUpdateTriggers(EState *estate, EPQState *epqstate,
 
 void
 ExecARUpdateTriggers(EState *estate, ResultRelInfo *relinfo,
-					 ItemPointer tupleid, HeapTuple newtuple,
+					 ItemPointer tupleid,
+					 HeapTuple fdw_trigtuple,
+					 HeapTuple newtuple,
 					 List *recheckIndexes)
 {
 	TriggerDesc *trigdesc = relinfo->ri_TrigDesc;
 
 	if (trigdesc && trigdesc->trig_update_after_row)
 	{
-		HeapTuple	trigtuple = GetTupleForTrigger(estate,
-												   NULL,
-												   relinfo,
-												   tupleid,
-												   LockTupleExclusive,
-												   NULL);
+		HeapTuple	trigtuple;
+
+		Assert(HeapTupleIsValid(fdw_trigtuple) ^ ItemPointerIsValid(tupleid));
+		if (fdw_trigtuple == NULL)
+			trigtuple = GetTupleForTrigger(estate,
+										   NULL,
+										   relinfo,
+										   tupleid,
+										   LockTupleExclusive,
+										   NULL);
+		else
+			trigtuple = fdw_trigtuple;
 
 		AfterTriggerSaveEvent(estate, relinfo, TRIGGER_EVENT_UPDATE,
 							  true, trigtuple, newtuple, recheckIndexes,
 							  GetModifiedColumns(relinfo, estate));
-		heap_freetuple(trigtuple);
+		if (trigtuple != fdw_trigtuple)
+			heap_freetuple(trigtuple);
 	}
 }
 
@@ -2942,13 +3008,22 @@ typedef SetConstraintStateData *SetConstraintState;
  * Per-trigger-event data
  *
  * The actual per-event data, AfterTriggerEventData, includes DONE/IN_PROGRESS
- * status bits and one or two tuple CTIDs.	Each event record also has an
- * associated AfterTriggerSharedData that is shared across all instances
- * of similar events within a "chunk".
+ * status bits and up to two tuple CTIDs.  Each event record also has an
+ * associated AfterTriggerSharedData that is shared across all instances of
+ * similar events within a "chunk".
  *
- * We arrange not to waste storage on ate_ctid2 for non-update events.
- * We could go further and not store either ctid for statement-level triggers,
- * but that seems unlikely to be worth the trouble.
+ * For row-level triggers, we arrange not to waste storage on unneeded ctid
+ * fields.  Updates of regular tables use two; inserts and deletes of regular
+ * tables use one; foreign tables always use zero and save the tuple(s) to a
+ * tuplestore.  AFTER_TRIGGER_FDW_FETCH directs AfterTriggerExecute() to
+ * retrieve a fresh tuple or pair of tuples from that tuplestore, while
+ * AFTER_TRIGGER_FDW_REUSE directs it to use the most-recently-retrieved
+ * tuple(s).  This permits storing tuples once regardless of the number of
+ * row-level triggers on a foreign table.
+ *
+ * Statement-level triggers always bear AFTER_TRIGGER_1CTID, though they
+ * require no ctid field.  We lack the flag bit space to neatly represent that
+ * distinct case, and it seems unlikely to be worth much trouble.
  *
  * Note: ats_firing_id is initially zero and is set to something else when
  * AFTER_TRIGGER_IN_PROGRESS is set.  It indicates which trigger firing
@@ -2963,9 +3038,14 @@ typedef uint32 TriggerFlags;
 
 #define AFTER_TRIGGER_OFFSET			0x0FFFFFFF		/* must be low-order
 														 * bits */
-#define AFTER_TRIGGER_2CTIDS			0x10000000
-#define AFTER_TRIGGER_DONE				0x20000000
-#define AFTER_TRIGGER_IN_PROGRESS		0x40000000
+#define AFTER_TRIGGER_DONE				0x10000000
+#define AFTER_TRIGGER_IN_PROGRESS		0x20000000
+/* bits describing the size and tuple sources of this event */
+#define AFTER_TRIGGER_FDW_REUSE			0x00000000
+#define AFTER_TRIGGER_FDW_FETCH			0x80000000
+#define AFTER_TRIGGER_1CTID				0x40000000
+#define AFTER_TRIGGER_2CTID				0xC0000000
+#define AFTER_TRIGGER_TUP_BITS			0xC0000000
 
 typedef struct AfterTriggerSharedData *AfterTriggerShared;
 
@@ -2986,16 +3066,25 @@ typedef struct AfterTriggerEventData
 	ItemPointerData ate_ctid2;	/* new updated tuple */
 } AfterTriggerEventData;
 
-/* This struct must exactly match the one above except for not having ctid2 */
+/* AfterTriggerEventData, minus ate_ctid2 */
 typedef struct AfterTriggerEventDataOneCtid
 {
 	TriggerFlags ate_flags;		/* status bits and offset to shared data */
 	ItemPointerData ate_ctid1;	/* inserted, deleted, or old updated tuple */
 }	AfterTriggerEventDataOneCtid;
 
+/* AfterTriggerEventData, minus ate_ctid1 and ate_ctid2 */
+typedef struct AfterTriggerEventDataZeroCtids
+{
+	TriggerFlags ate_flags;		/* status bits and offset to shared data */
+} AfterTriggerEventDataZeroCtids;
+
 #define SizeofTriggerEvent(evt) \
-	(((evt)->ate_flags & AFTER_TRIGGER_2CTIDS) ? \
-	 sizeof(AfterTriggerEventData) : sizeof(AfterTriggerEventDataOneCtid))
+	(((evt)->ate_flags & AFTER_TRIGGER_TUP_BITS) == AFTER_TRIGGER_2CTID ? \
+	 sizeof(AfterTriggerEventData) : \
+		((evt)->ate_flags & AFTER_TRIGGER_TUP_BITS) == AFTER_TRIGGER_1CTID ? \
+		sizeof(AfterTriggerEventDataOneCtid) : \
+			sizeof(AfterTriggerEventDataZeroCtids))
 
 #define GetTriggerSharedData(evt) \
 	((AfterTriggerShared) ((char *) (evt) + ((evt)->ate_flags & AFTER_TRIGGER_OFFSET)))
@@ -3068,7 +3157,11 @@ typedef struct AfterTriggerEventList
  * immediate-mode triggers, and append any deferred events to the main events
  * list.
  *
- * maxquerydepth is just the allocated length of query_stack.
+ * fdw_tuplestores[query_depth] is a tuplestore containing the foreign tuples
+ * needed for the current query.
+ *
+ * maxquerydepth is just the allocated length of query_stack and
+ * fdw_tuplestores.
  *
  * state_stack is a stack of pointers to saved copies of the SET CONSTRAINTS
  * state data; each subtransaction level that modifies that state first
@@ -3097,6 +3190,7 @@ typedef struct AfterTriggersData
 	AfterTriggerEventList events;		/* deferred-event list */
 	int			query_depth;	/* current query list index */
 	AfterTriggerEventList *query_stack; /* events pending from each query */
+	Tuplestorestate **fdw_tuplestores;	/* foreign tuples from each query */
 	int			maxquerydepth;	/* allocated len of above array */
 	MemoryContext event_cxt;	/* memory context for events, if any */
 
@@ -3113,18 +3207,60 @@ typedef AfterTriggersData *AfterTriggers;
 
 static AfterTriggers afterTriggers;
 
-
 static void AfterTriggerExecute(AfterTriggerEvent event,
 					Relation rel, TriggerDesc *trigdesc,
 					FmgrInfo *finfo,
 					Instrumentation *instr,
-					MemoryContext per_tuple_context);
+					MemoryContext per_tuple_context,
+					TupleTableSlot *trig_tuple_slot1,
+					TupleTableSlot *trig_tuple_slot2);
 static SetConstraintState SetConstraintStateCreate(int numalloc);
 static SetConstraintState SetConstraintStateCopy(SetConstraintState state);
 static SetConstraintState SetConstraintStateAddItem(SetConstraintState state,
 						  Oid tgoid, bool tgisdeferred);
 
 
+/*
+ * Gets the current query fdw tuplestore and initializes it if necessary
+ */
+static Tuplestorestate *
+GetCurrentFDWTuplestore()
+{
+	Tuplestorestate *ret;
+
+	ret = afterTriggers->fdw_tuplestores[afterTriggers->query_depth];
+	if (ret == NULL)
+	{
+		MemoryContext oldcxt;
+		ResourceOwner saveResourceOwner;
+
+		/*
+		 * Make the tuplestore valid until end of transaction.  This is the
+		 * allocation lifespan of the associated events list, but we really
+		 * only need it until AfterTriggerEndQuery().
+		 */
+		oldcxt = MemoryContextSwitchTo(TopTransactionContext);
+		saveResourceOwner = CurrentResourceOwner;
+		PG_TRY();
+		{
+			CurrentResourceOwner = TopTransactionResourceOwner;
+			ret = tuplestore_begin_heap(false, false, work_mem);
+		}
+		PG_CATCH();
+		{
+			CurrentResourceOwner = saveResourceOwner;
+			PG_RE_THROW();
+		}
+		PG_END_TRY();
+		CurrentResourceOwner = saveResourceOwner;
+		MemoryContextSwitchTo(oldcxt);
+
+		afterTriggers->fdw_tuplestores[afterTriggers->query_depth] = ret;
+	}
+
+	return ret;
+}
+
 /* ----------
  * afterTriggerCheckState()
  *
@@ -3365,13 +3501,17 @@ afterTriggerRestoreEventList(AfterTriggerEventList *events,
  *	instr: array of EXPLAIN ANALYZE instrumentation nodes (one per trigger),
  *		or NULL if no instrumentation is wanted.
  *	per_tuple_context: memory context to call trigger function in.
+ *	trig_tuple_slot1: scratch slot for tg_trigtuple (foreign tables only)
+ *	trig_tuple_slot2: scratch slot for tg_newtuple (foreign tables only)
  * ----------
  */
 static void
 AfterTriggerExecute(AfterTriggerEvent event,
 					Relation rel, TriggerDesc *trigdesc,
 					FmgrInfo *finfo, Instrumentation *instr,
-					MemoryContext per_tuple_context)
+					MemoryContext per_tuple_context,
+					TupleTableSlot *trig_tuple_slot1,
+					TupleTableSlot *trig_tuple_slot2)
 {
 	AfterTriggerShared evtshared = GetTriggerSharedData(event);
 	Oid			tgoid = evtshared->ats_tgoid;
@@ -3408,34 +3548,76 @@ AfterTriggerExecute(AfterTriggerEvent event,
 	/*
 	 * Fetch the required tuple(s).
 	 */
-	if (ItemPointerIsValid(&(event->ate_ctid1)))
+	switch (event->ate_flags & AFTER_TRIGGER_TUP_BITS)
 	{
-		ItemPointerCopy(&(event->ate_ctid1), &(tuple1.t_self));
-		if (!heap_fetch(rel, SnapshotAny, &tuple1, &buffer1, false, NULL))
-			elog(ERROR, "failed to fetch tuple1 for AFTER trigger");
-		LocTriggerData.tg_trigtuple = &tuple1;
-		LocTriggerData.tg_trigtuplebuf = buffer1;
-	}
-	else
-	{
-		LocTriggerData.tg_trigtuple = NULL;
-		LocTriggerData.tg_trigtuplebuf = InvalidBuffer;
-	}
+		case AFTER_TRIGGER_FDW_FETCH:
+			{
+				Tuplestorestate *fdw_tuplestore = GetCurrentFDWTuplestore();
 
-	/* don't touch ctid2 if not there */
-	if ((event->ate_flags & AFTER_TRIGGER_2CTIDS) &&
-		ItemPointerIsValid(&(event->ate_ctid2)))
-	{
-		ItemPointerCopy(&(event->ate_ctid2), &(tuple2.t_self));
-		if (!heap_fetch(rel, SnapshotAny, &tuple2, &buffer2, false, NULL))
-			elog(ERROR, "failed to fetch tuple2 for AFTER trigger");
-		LocTriggerData.tg_newtuple = &tuple2;
-		LocTriggerData.tg_newtuplebuf = buffer2;
-	}
-	else
-	{
-		LocTriggerData.tg_newtuple = NULL;
-		LocTriggerData.tg_newtuplebuf = InvalidBuffer;
+				if (!tuplestore_gettupleslot(fdw_tuplestore, true, false,
+											 trig_tuple_slot1))
+					elog(ERROR, "failed to fetch tuple1 for AFTER trigger");
+
+				if ((evtshared->ats_event & TRIGGER_EVENT_OPMASK) ==
+					TRIGGER_EVENT_UPDATE &&
+					!tuplestore_gettupleslot(fdw_tuplestore, true, false,
+											 trig_tuple_slot2))
+					elog(ERROR, "failed to fetch tuple2 for AFTER trigger");
+			}
+			/* fall through */
+		case AFTER_TRIGGER_FDW_REUSE:
+			/*
+			 * Using ExecMaterializeSlot() rather than ExecFetchSlotTuple()
+			 * ensures that tg_trigtuple does not reference tuplestore memory.
+			 * (It is formally possible for the trigger function to queue
+			 * trigger events that add to the same tuplestore, which can push
+			 * other tuples out of memory.)  The distinction is academic,
+			 * because we start with a minimal tuple that ExecFetchSlotTuple()
+			 * must materialize anyway.
+			 */
+			LocTriggerData.tg_trigtuple =
+				ExecMaterializeSlot(trig_tuple_slot1);
+			LocTriggerData.tg_trigtuplebuf = InvalidBuffer;
+
+			LocTriggerData.tg_newtuple =
+				((evtshared->ats_event & TRIGGER_EVENT_OPMASK) ==
+				 TRIGGER_EVENT_UPDATE) ?
+				ExecMaterializeSlot(trig_tuple_slot2) : NULL;
+			LocTriggerData.tg_newtuplebuf = InvalidBuffer;
+
+			break;
+
+		default:
+			if (ItemPointerIsValid(&(event->ate_ctid1)))
+			{
+				ItemPointerCopy(&(event->ate_ctid1), &(tuple1.t_self));
+				if (!heap_fetch(rel, SnapshotAny, &tuple1, &buffer1, false, NULL))
+					elog(ERROR, "failed to fetch tuple1 for AFTER trigger");
+				LocTriggerData.tg_trigtuple = &tuple1;
+				LocTriggerData.tg_trigtuplebuf = buffer1;
+			}
+			else
+			{
+				LocTriggerData.tg_trigtuple = NULL;
+				LocTriggerData.tg_trigtuplebuf = InvalidBuffer;
+			}
+
+			/* don't touch ctid2 if not there */
+			if ((event->ate_flags & AFTER_TRIGGER_TUP_BITS) ==
+				AFTER_TRIGGER_2CTID &&
+				ItemPointerIsValid(&(event->ate_ctid2)))
+			{
+				ItemPointerCopy(&(event->ate_ctid2), &(tuple2.t_self));
+				if (!heap_fetch(rel, SnapshotAny, &tuple2, &buffer2, false, NULL))
+					elog(ERROR, "failed to fetch tuple2 for AFTER trigger");
+				LocTriggerData.tg_newtuple = &tuple2;
+				LocTriggerData.tg_newtuplebuf = buffer2;
+			}
+			else
+			{
+				LocTriggerData.tg_newtuple = NULL;
+				LocTriggerData.tg_newtuplebuf = InvalidBuffer;
+			}
 	}
 
 	/*
@@ -3457,7 +3639,9 @@ AfterTriggerExecute(AfterTriggerEvent event,
 								   finfo,
 								   NULL,
 								   per_tuple_context);
-	if (rettuple != NULL && rettuple != &tuple1 && rettuple != &tuple2)
+	if (rettuple != NULL &&
+		rettuple != LocTriggerData.tg_trigtuple &&
+		rettuple != LocTriggerData.tg_newtuple)
 		heap_freetuple(rettuple);
 
 	/*
@@ -3577,6 +3761,8 @@ afterTriggerInvokeEvents(AfterTriggerEventList *events,
 	TriggerDesc *trigdesc = NULL;
 	FmgrInfo   *finfo = NULL;
 	Instrumentation *instr = NULL;
+	TupleTableSlot *slot1 = NULL,
+			   *slot2 = NULL;
 
 	/* Make a local EState if need be */
 	if (estate == NULL)
@@ -3621,6 +3807,16 @@ afterTriggerInvokeEvents(AfterTriggerEventList *events,
 					trigdesc = rInfo->ri_TrigDesc;
 					finfo = rInfo->ri_TrigFunctions;
 					instr = rInfo->ri_TrigInstrument;
+					if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
+					{
+						if (slot1 != NULL)
+						{
+							ExecDropSingleTupleTableSlot(slot1);
+							ExecDropSingleTupleTableSlot(slot2);
+						}
+						slot1 = MakeSingleTupleTableSlot(rel->rd_att);
+						slot2 = MakeSingleTupleTableSlot(rel->rd_att);
+					}
 					if (trigdesc == NULL)		/* should not happen */
 						elog(ERROR, "relation %u has no triggers",
 							 evtshared->ats_relid);
@@ -3632,7 +3828,7 @@ afterTriggerInvokeEvents(AfterTriggerEventList *events,
 				 * won't try to re-fire it.
 				 */
 				AfterTriggerExecute(event, rel, trigdesc, finfo, instr,
-									per_tuple_context);
+									per_tuple_context, slot1, slot2);
 
 				/*
 				 * Mark the event as done.
@@ -3663,6 +3859,11 @@ afterTriggerInvokeEvents(AfterTriggerEventList *events,
 				events->tailfree = chunk->freeptr;
 		}
 	}
+	if (slot1 != NULL)
+	{
+		ExecDropSingleTupleTableSlot(slot1);
+		ExecDropSingleTupleTableSlot(slot2);
+	}
 
 	/* Release working resources */
 	MemoryContextDelete(per_tuple_context);
@@ -3712,10 +3913,13 @@ AfterTriggerBeginXact(void)
 	afterTriggers->events.tailfree = NULL;
 	afterTriggers->query_depth = -1;
 
-	/* We initialize the query stack to a reasonable size */
+	/* We initialize the arrays to a reasonable size */
 	afterTriggers->query_stack = (AfterTriggerEventList *)
 		MemoryContextAlloc(TopTransactionContext,
 						   8 * sizeof(AfterTriggerEventList));
+	afterTriggers->fdw_tuplestores = (Tuplestorestate **)
+		MemoryContextAllocZero(TopTransactionContext,
+							   8 * sizeof(Tuplestorestate *));
 	afterTriggers->maxquerydepth = 8;
 
 	/* Context for events is created only when needed */
@@ -3756,11 +3960,18 @@ AfterTriggerBeginQuery(void)
 	if (afterTriggers->query_depth >= afterTriggers->maxquerydepth)
 	{
 		/* repalloc will keep the stack in the same context */
-		int			new_alloc = afterTriggers->maxquerydepth * 2;
+		int			old_alloc = afterTriggers->maxquerydepth;
+		int			new_alloc = old_alloc * 2;
 
 		afterTriggers->query_stack = (AfterTriggerEventList *)
 			repalloc(afterTriggers->query_stack,
 					 new_alloc * sizeof(AfterTriggerEventList));
+		afterTriggers->fdw_tuplestores = (Tuplestorestate **)
+			repalloc(afterTriggers->fdw_tuplestores,
+					 new_alloc * sizeof(Tuplestorestate *));
+		/* Clear newly-allocated slots for subsequent lazy initialization. */
+		memset(afterTriggers->fdw_tuplestores + old_alloc,
+			   0, (new_alloc - old_alloc) * sizeof(Tuplestorestate *));
 		afterTriggers->maxquerydepth = new_alloc;
 	}
 
@@ -3788,6 +3999,7 @@ void
 AfterTriggerEndQuery(EState *estate)
 {
 	AfterTriggerEventList *events;
+	Tuplestorestate *fdw_tuplestore;
 
 	/* Must be inside a transaction */
 	Assert(afterTriggers != NULL);
@@ -3832,7 +4044,13 @@ AfterTriggerEndQuery(EState *estate)
 			break;
 	}
 
-	/* Release query-local storage for events */
+	/* Release query-local storage for events, including tuplestore if any */
+	fdw_tuplestore = afterTriggers->fdw_tuplestores[afterTriggers->query_depth];
+	if (fdw_tuplestore)
+	{
+		tuplestore_end(fdw_tuplestore);
+		afterTriggers->fdw_tuplestores[afterTriggers->query_depth] = NULL;
+	}
 	afterTriggerFreeEventList(&afterTriggers->query_stack[afterTriggers->query_depth]);
 
 	afterTriggers->query_depth--;
@@ -4056,6 +4274,15 @@ AfterTriggerEndSubXact(bool isCommit)
 		 */
 		while (afterTriggers->query_depth > afterTriggers->depth_stack[my_level])
 		{
+			Tuplestorestate *ts;
+
+			ts = afterTriggers->fdw_tuplestores[afterTriggers->query_depth];
+			if (ts)
+			{
+				tuplestore_end(ts);
+				afterTriggers->fdw_tuplestores[afterTriggers->query_depth] = NULL;
+			}
+
 			afterTriggerFreeEventList(&afterTriggers->query_stack[afterTriggers->query_depth]);
 			afterTriggers->query_depth--;
 		}
@@ -4552,9 +4779,11 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 	TriggerDesc *trigdesc = relinfo->ri_TrigDesc;
 	AfterTriggerEventData new_event;
 	AfterTriggerSharedData new_shared;
+	char		relkind = relinfo->ri_RelationDesc->rd_rel->relkind;
 	int			tgtype_event;
 	int			tgtype_level;
 	int			i;
+	Tuplestorestate *fdw_tuplestore = NULL;
 
 	/*
 	 * Check state.  We use normal tests not Asserts because it is possible to
@@ -4573,7 +4802,6 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 	 * validation is important to make sure we don't walk off the edge of our
 	 * arrays.
 	 */
-	new_event.ate_flags = 0;
 	switch (event)
 	{
 		case TRIGGER_EVENT_INSERT:
@@ -4618,7 +4846,6 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 				Assert(newtup != NULL);
 				ItemPointerCopy(&(oldtup->t_self), &(new_event.ate_ctid1));
 				ItemPointerCopy(&(newtup->t_self), &(new_event.ate_ctid2));
-				new_event.ate_flags |= AFTER_TRIGGER_2CTIDS;
 			}
 			else
 			{
@@ -4641,6 +4868,11 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 			break;
 	}
 
+	if (!(relkind == RELKIND_FOREIGN_TABLE && row_trigger))
+		new_event.ate_flags = (row_trigger && event == TRIGGER_EVENT_UPDATE) ?
+			AFTER_TRIGGER_2CTID : AFTER_TRIGGER_1CTID;
+	/* else, we'll initialize ate_flags for each trigger */
+
 	tgtype_level = (row_trigger ? TRIGGER_TYPE_ROW : TRIGGER_TYPE_STATEMENT);
 
 	for (i = 0; i < trigdesc->numtriggers; i++)
@@ -4656,6 +4888,18 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 							modifiedCols, oldtup, newtup))
 			continue;
 
+		if (relkind == RELKIND_FOREIGN_TABLE && row_trigger)
+		{
+			if (fdw_tuplestore == NULL)
+			{
+				fdw_tuplestore = GetCurrentFDWTuplestore();
+				new_event.ate_flags = AFTER_TRIGGER_FDW_FETCH;
+			}
+			else
+				/* subsequent event for the same tuple */
+				new_event.ate_flags = AFTER_TRIGGER_FDW_REUSE;
+		}
+
 		/*
 		 * If the trigger is a foreign key enforcement trigger, there are
 		 * certain cases where we can skip queueing the event because we can
@@ -4717,6 +4961,19 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 		afterTriggerAddEvent(&afterTriggers->query_stack[afterTriggers->query_depth],
 							 &new_event, &new_shared);
 	}
+
+	/*
+	 * Finally, spool any foreign tuple(s).  The tuplestore squashes them to
+	 * minimal tuples, so this loses any system columns.  The executor lost
+	 * those columns before us, for an unrelated reason, so this is fine.
+	 */
+	if (fdw_tuplestore)
+	{
+		if (oldtup != NULL)
+			tuplestore_puttuple(fdw_tuplestore, oldtup);
+		if (newtup != NULL)
+			tuplestore_puttuple(fdw_tuplestore, newtup);
+	}
 }
 
 Datum