Function ExecSplitUpdate

src/backend/executor/nodeSplitUpdate.c:169–214

* Splits every TupleTableSlot into two TupleTableSlots: DELETE and INSERT. */

 * Splits every TupleTableSlot into two TupleTableSlots: DELETE and INSERT.
 */
static TupleTableSlot *
ExecSplitUpdate(PlanState *pstate)
{
	SplitUpdateState *node = castNode(SplitUpdateState, pstate);
	PlanState *outerNode = outerPlanState(node);
	SplitUpdate *plannode = (SplitUpdate *) node->ps.plan;

	TupleTableSlot *slot = NULL;
	TupleTableSlot *result = NULL;

	Assert(outerNode != NULL);

	/* Returns INSERT TupleTableSlot. */
	if (!node->processInsert)
	{
		result = node->insertTuple;

		node->processInsert = true;
	}
	else
	{
		/* Creates both TupleTableSlots. Returns DELETE TupleTableSlots.*/
		slot = ExecProcNode(outerNode);

		if (TupIsNull(slot))
		{
			return NULL;
		}

		/* `Split' update into delete and insert */
		slot_getallattrs(slot);
		Datum	   *values = slot->tts_values;
		bool	   *nulls = slot->tts_isnull;

		ExecStoreAllNullTuple(node->deleteTuple);
		ExecStoreAllNullTuple(node->insertTuple);

		SplitTupleTableSlot(slot, plannode->plan.targetlist, plannode, node, values, nulls);

		result = node->deleteTuple;
		node->processInsert = false;

	}

	return result;
}

/*
 * Init SplitUpdate Node. A memory context is created to hold Split Tuples.