Testcase Coverage for OUTPUT clause

We are dealing with a critical crash bug in Babelfish's EPQ (EvalPlanQual) handling during concurrent UPDATE operations with OUTPUT clauses. The crash occurs when two sessions simultaneously modify the same row, where the column is of type "varchar" causing tuple alignment problems during EPQ re-evaluation. This is a memory corruption issue where PostgreSQL's EPQ mechanism fails to properly handle tuple structure changes when Babelfish processes OUTPUT clauses, leading to segmentation faults or assertion failures.

Author: herambh-shah

src/backend/executor/nodeModifyTable.c

@@ -915,11 +915,6 @@ ExecInsert(ModifyTableContext *context,
 			return NULL;		/* "do nothing" */
 	}
 
-	/* Process RETURNING if present */
-	if (resultRelInfo->ri_projectReturning && sql_dialect == SQL_DIALECT_TSQL)
-		result = ExecProcessReturning(context, resultRelInfo, CMD_INSERT,
-									  NULL, slot, planSlot);
-
 	/* INSTEAD OF ROW INSERT Triggers */
 	if (resultRelInfo->ri_TrigDesc &&
 		resultRelInfo->ri_TrigDesc->trig_insert_instead_row)
@@ -1603,7 +1598,6 @@ ExecDelete(ModifyTableContext *context,
 	Relation	resultRelationDesc = resultRelInfo->ri_RelationDesc;
 	TupleTableSlot *slot = NULL;
 	TM_Result	result;
-	TupleTableSlot *rslot_output = NULL;
 	bool		saveOld;
 
 	if (tupleDeleted)
@@ -1617,44 +1611,6 @@ ExecDelete(ModifyTableContext *context,
 							epqreturnslot, tmresult))
 		return NULL;
 
-	/* Process RETURNING if present and if requested */
-	if (processReturning && resultRelInfo->ri_projectReturning && sql_dialect == SQL_DIALECT_TSQL)
-	{
-		/*
-		 * We have to put the target tuple into a slot, which means first we
-		 * gotta fetch it.  We can use the trigger tuple slot.
-		 */
-		if (resultRelInfo->ri_FdwRoutine)
-		{
-			/* FDW must have provided a slot containing the deleted row */
-			Assert(!TupIsNull(slot));
-		}
-		else
-		{
-			slot = ExecGetReturningSlot(estate, resultRelInfo);
-			if (oldtuple != NULL)
-			{
-				ExecForceStoreHeapTuple(oldtuple, slot, false);
-			}
-			else
-			{
-				if (!table_tuple_fetch_row_version(resultRelationDesc, tupleid,
-												   SnapshotAny, slot))
-					elog(ERROR, "failed to fetch deleted tuple for DELETE RETURNING");
-			}
-		}
-		rslot_output = ExecProcessReturning(context, resultRelInfo, CMD_DELETE,
-									 slot, NULL, context->planSlot);
-
-		/*
-		 * Before releasing the target tuple again, make sure rslot has a
-		 * local copy of any pass-by-reference values.
-		 */
-		ExecMaterializeSlot(rslot_output);
-
-		ExecClearTuple(slot);
-	}
-
 	if (resultRelInfo->ri_TrigDesc &&
 		resultRelInfo->ri_TrigDesc->trig_delete_instead_statement &&
 		sql_dialect == SQL_DIALECT_TSQL &&
@@ -1899,7 +1855,7 @@ ExecDelete(ModifyTableContext *context,
 	saveOld = changingPart && resultRelInfo->ri_projectReturning &&
 		resultRelInfo->ri_projectReturning->pi_state.flags & EEO_FLAG_HAS_OLD;
 
-	if (resultRelInfo->ri_projectReturning && (processReturning || saveOld) && sql_dialect != SQL_DIALECT_TSQL)
+	if (resultRelInfo->ri_projectReturning && (processReturning || saveOld))
 	{
 		/*
 		 * We have to put the target tuple into a slot, which means first we
@@ -1974,9 +1930,6 @@ ExecDelete(ModifyTableContext *context,
 		return rslot;
 	}
 
-	if (processReturning && resultRelInfo->ri_projectReturning && rslot_output)
-		return rslot_output;
-
 	return NULL;
 }
 
@@ -2539,7 +2492,6 @@ ExecUpdate(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
 	Relation	resultRelationDesc = resultRelInfo->ri_RelationDesc;
 	UpdateContext updateCxt = {0};
 	TM_Result	result;
-	TupleTableSlot *rslot = NULL;
 
 	/*
 	 * abort the operation if not running transactions
@@ -2554,11 +2506,6 @@ ExecUpdate(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
 	if (!ExecUpdatePrologue(context, resultRelInfo, tupleid, oldtuple, slot, NULL))
 		return NULL;
 
-	/* Process RETURNING if present */
-	if (resultRelInfo->ri_projectReturning && sql_dialect == SQL_DIALECT_TSQL)
-		rslot = ExecProcessReturning(context, resultRelInfo, CMD_UPDATE,
-									oldSlot, slot, context->planSlot);
-
 	if (resultRelInfo->ri_TrigDesc &&
 		resultRelInfo->ri_TrigDesc->trig_update_instead_statement &&
 		sql_dialect == SQL_DIALECT_TSQL && bbfViewHasInsteadofTrigger_hook && (bbfViewHasInsteadofTrigger_hook)(resultRelationDesc, CMD_UPDATE) &&
@@ -2781,13 +2728,10 @@ ExecUpdate(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
 					   slot);
 
 	/* Process RETURNING if present */
-	if (resultRelInfo->ri_projectReturning && sql_dialect != SQL_DIALECT_TSQL)
+	if (resultRelInfo->ri_projectReturning)
 		return ExecProcessReturning(context, resultRelInfo, CMD_UPDATE,
 									oldSlot, slot, context->planSlot);
 
-	if (resultRelInfo->ri_projectReturning)
-		return rslot;
-
 	return NULL;
 }