Add API of sorts for transition table handling in trigger.c

Preparatory patch for further additions in this area, particularly to
allow MERGE to have separate transition tables for each action.

Author: Pavan Deolasee <pavan.deolasee@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/CABOikdNj+8HEJ5D8tu56mrPkjHVRrBb2_cdKWwpiYNcjXgDw8g@mail.gmail.com
Discussion: https://postgr.es/m/20201231134736.GA25392@alvherre.pgsql

Author: alvherre

src/backend/commands/trigger.c

@@ -3772,6 +3772,16 @@ static AfterTriggersTableData *GetAfterTriggersTableData(Oid relid,
 														 CmdType cmdType);
 static TupleTableSlot *GetAfterTriggersStoreSlot(AfterTriggersTableData *table,
 												 TupleDesc tupdesc);
+static Tuplestorestate *GetAfterTriggersTransitionTable(int event,
+														TupleTableSlot *oldslot,
+														TupleTableSlot *newslot,
+														TransitionCaptureState *transition_capture);
+static void TransitionTableAddTuple(EState *estate,
+									TransitionCaptureState *transition_capture,
+									ResultRelInfo *relinfo,
+									TupleTableSlot *slot,
+									TupleTableSlot *original_insert_tuple,
+									Tuplestorestate *tuplestore);
 static void AfterTriggerFreeQuery(AfterTriggersQueryData *qs);
 static SetConstraintState SetConstraintStateCreate(int numalloc);
 static SetConstraintState SetConstraintStateCopy(SetConstraintState state);
@@ -5158,6 +5168,92 @@ AfterTriggerEndSubXact(bool isCommit)
 	}
 }
 
+/*
+ * Get the transition table for the given event and depending on whether we are
+ * processing the old or the new tuple.
+ */
+static Tuplestorestate *
+GetAfterTriggersTransitionTable(int event,
+								TupleTableSlot *oldslot,
+								TupleTableSlot *newslot,
+								TransitionCaptureState *transition_capture)
+{
+	Tuplestorestate *tuplestore = NULL;
+	bool		delete_old_table = transition_capture->tcs_delete_old_table;
+	bool		update_old_table = transition_capture->tcs_update_old_table;
+	bool		update_new_table = transition_capture->tcs_update_new_table;
+	bool		insert_new_table = transition_capture->tcs_insert_new_table;
+
+	/*
+	 * For INSERT events NEW should be non-NULL, for DELETE events OLD should
+	 * be non-NULL, whereas for UPDATE events normally both OLD and NEW are
+	 * non-NULL.  But for UPDATE events fired for capturing transition tuples
+	 * during UPDATE partition-key row movement, OLD is NULL when the event is
+	 * for a row being inserted, whereas NEW is NULL when the event is for a
+	 * row being deleted.
+	 */
+	Assert(!(event == TRIGGER_EVENT_DELETE && delete_old_table &&
+			 TupIsNull(oldslot)));
+	Assert(!(event == TRIGGER_EVENT_INSERT && insert_new_table &&
+			 TupIsNull(newslot)));
+
+	if (!TupIsNull(oldslot))
+	{
+		Assert(TupIsNull(newslot));
+		if (event == TRIGGER_EVENT_DELETE && delete_old_table)
+			tuplestore = transition_capture->tcs_private->old_tuplestore;
+		else if (event == TRIGGER_EVENT_UPDATE && update_old_table)
+			tuplestore = transition_capture->tcs_private->old_tuplestore;
+	}
+	else if (!TupIsNull(newslot))
+	{
+		Assert(TupIsNull(oldslot));
+		if (event == TRIGGER_EVENT_INSERT && insert_new_table)
+			tuplestore = transition_capture->tcs_private->new_tuplestore;
+		else if (event == TRIGGER_EVENT_UPDATE && update_new_table)
+			tuplestore = transition_capture->tcs_private->new_tuplestore;
+	}
+
+	return tuplestore;
+}
+
+/*
+ * Add the given heap tuple to the given tuplestore, applying the conversion
+ * map if necessary.
+ *
+ * If original_insert_tuple is given, we can add that tuple without conversion.
+ */
+static void
+TransitionTableAddTuple(EState *estate,
+						TransitionCaptureState *transition_capture,
+						ResultRelInfo *relinfo,
+						TupleTableSlot *slot,
+						TupleTableSlot *original_insert_tuple,
+						Tuplestorestate *tuplestore)
+{
+	TupleConversionMap *map;
+
+	/*
+	 * Nothing needs to be done if we don't have a tuplestore.
+	 */
+	if (tuplestore == NULL)
+		return;
+
+	if (original_insert_tuple)
+		tuplestore_puttupleslot(tuplestore, original_insert_tuple);
+	else if ((map = ExecGetChildToRootMap(relinfo)) != NULL)
+	{
+		AfterTriggersTableData *table = transition_capture->tcs_private;
+		TupleTableSlot *storeslot;
+
+		storeslot = GetAfterTriggersStoreSlot(table, map->outdesc);
+		execute_attr_map_slot(map->attrMap, slot, storeslot);
+		tuplestore_puttupleslot(tuplestore, storeslot);
+	}
+	else
+		tuplestore_puttupleslot(tuplestore, slot);
+}
+
 /* ----------
  * AfterTriggerEnlargeQueryState()
  *
@@ -5650,7 +5746,6 @@ AfterTriggerPendingOnRel(Oid relid)
 	return false;
 }
 
-
 /* ----------
  * AfterTriggerSaveEvent()
  *
@@ -5709,68 +5804,39 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 	 */
 	if (row_trigger && transition_capture != NULL)
 	{
-		TupleTableSlot *original_insert_tuple = transition_capture->tcs_original_insert_tuple;
-		TupleConversionMap *map = ExecGetChildToRootMap(relinfo);
-		bool		delete_old_table = transition_capture->tcs_delete_old_table;
-		bool		update_old_table = transition_capture->tcs_update_old_table;
-		bool		update_new_table = transition_capture->tcs_update_new_table;
-		bool		insert_new_table = transition_capture->tcs_insert_new_table;
 
 		/*
-		 * For INSERT events NEW should be non-NULL, for DELETE events OLD
-		 * should be non-NULL, whereas for UPDATE events normally both OLD and
-		 * NEW are non-NULL.  But for UPDATE events fired for capturing
-		 * transition tuples during UPDATE partition-key row movement, OLD is
-		 * NULL when the event is for a row being inserted, whereas NEW is
-		 * NULL when the event is for a row being deleted.
+		 * Capture the old tuple in the appropriate transition table based on
+		 * the event.
 		 */
-		Assert(!(event == TRIGGER_EVENT_DELETE && delete_old_table &&
-				 TupIsNull(oldslot)));
-		Assert(!(event == TRIGGER_EVENT_INSERT && insert_new_table &&
-				 TupIsNull(newslot)));
-
-		if (!TupIsNull(oldslot) &&
-			((event == TRIGGER_EVENT_DELETE && delete_old_table) ||
-			 (event == TRIGGER_EVENT_UPDATE && update_old_table)))
+		if (!TupIsNull(oldslot))
 		{
 			Tuplestorestate *old_tuplestore;
 
-			old_tuplestore = transition_capture->tcs_private->old_tuplestore;
-
-			if (map != NULL)
-			{
-				AfterTriggersTableData *table = transition_capture->tcs_private;
-				TupleTableSlot *storeslot;
-
-				storeslot = GetAfterTriggersStoreSlot(table, map->outdesc);
-				execute_attr_map_slot(map->attrMap, oldslot, storeslot);
-				tuplestore_puttupleslot(old_tuplestore, storeslot);
-			}
-			else
-				tuplestore_puttupleslot(old_tuplestore, oldslot);
+			old_tuplestore = GetAfterTriggersTransitionTable(event,
+															 oldslot,
+															 NULL,
+															 transition_capture);
+			TransitionTableAddTuple(estate, transition_capture, relinfo,
+									oldslot, NULL, old_tuplestore);
 		}
-		if (!TupIsNull(newslot) &&
-			((event == TRIGGER_EVENT_INSERT && insert_new_table) ||
-			 (event == TRIGGER_EVENT_UPDATE && update_new_table)))
+
+		/*
+		 * Capture the new tuple in the appropriate transition table based on
+		 * the event.
+		 */
+		if (!TupIsNull(newslot))
 		{
 			Tuplestorestate *new_tuplestore;
 
-			new_tuplestore = transition_capture->tcs_private->new_tuplestore;
-
-			if (original_insert_tuple != NULL)
-				tuplestore_puttupleslot(new_tuplestore,
-										original_insert_tuple);
-			else if (map != NULL)
-			{
-				AfterTriggersTableData *table = transition_capture->tcs_private;
-				TupleTableSlot *storeslot;
-
-				storeslot = GetAfterTriggersStoreSlot(table, map->outdesc);
-				execute_attr_map_slot(map->attrMap, newslot, storeslot);
-				tuplestore_puttupleslot(new_tuplestore, storeslot);
-			}
-			else
-				tuplestore_puttupleslot(new_tuplestore, newslot);
+			new_tuplestore = GetAfterTriggersTransitionTable(event,
+															 NULL,
+															 newslot,
+															 transition_capture);
+			TransitionTableAddTuple(estate, transition_capture, relinfo,
+									newslot,
+									transition_capture->tcs_original_insert_tuple,
+									new_tuplestore);
 		}
 
 		/*