[BABEL] Fixes for Babelfish triggers after community commit c5fc17ddacc

Community commit c5fc17ddacc introduced a fix for CTEs with DMLs not
being inserted into the transition tables. For this fix, the previous
tcs_private field is now split into individual ins, upd and del field
each with the old and new tuplestore.

TSQL triggers are implicitly created with new "inserted" and old
"deleted" transition tables even for insert and delete triggers and both
are referenceble in the trigger function. With the splitting of the
tcs_private field we no longer intialize the old ins tuplestore and new
del tuplestore. However, since these transition tables are atleast
accessible from a TSQL trigger, we should have an empty tuplestore for both
of them anyway.

Since these will be empty as per behaviour of INSERT and DELETE triggers,
we are okay with simply creating an empty tuplestore for them.

Signed-off-by: Ayush Shah <ayushdsh@amazon.com>

cr: https://code.amazon.com/reviews/CR-256859140

Author: ayushdsh

src/backend/commands/trigger.c

@@ -5445,6 +5445,25 @@ MakeTransitionCaptureState(TriggerDesc *trigdesc, Oid relid, CmdType cmdType)
 	if (need_new_ins && ins_table->new_tuplestore == NULL)
 		ins_table->new_tuplestore = tuplestore_begin_heap(false, false, work_mem);
 
+	/*
+	 * BABELFISH: TSQL triggers are implicitly created with and old and new transition tables
+	 * called "deleted" and "inserted" respectively. Since we've replaced the tcs_private field 
+	 * with individual ins, upd, del fields, with INSERTs we no longer create an empty tuplestore
+	 * for old transition table and similarly for DELETEs we don't create a new one. However, 
+	 * since these transition tables are atleast accessible from a TSQL trigger, we should have an empty
+	 * tuplestore for both of them anyway.
+	 *
+	 * Since these will be empty as per behaviour of INSERT and DELETE triggers, we are okay with
+	 * simply creating an empty tuplestore for them.
+	 */
+	if (sql_dialect == SQL_DIALECT_TSQL)
+	{
+		if (ins_table && ins_table->old_tuplestore == NULL)
+			ins_table->old_tuplestore = tuplestore_begin_heap(false, false, work_mem);
+		if (del_table && del_table->new_tuplestore == NULL)
+			del_table->new_tuplestore = tuplestore_begin_heap(false, false, work_mem);
+	}
+
 	CurrentResourceOwner = saveResourceOwner;
 	MemoryContextSwitchTo(oldcxt);