Function initialize_phase

src/backend/executor/nodeAgg.c:513–573

* Switch to phase "newphase", which must either be 0 or 1 (to reset) or * current_phase + 1. Juggle the tuplesorts accordingly. * * Phase 0 is for hashing, which we currently handle last in the AGG_MIXED * case, so when entering phase 0, all we need to do is drop open sorts. */

 * case, so when entering phase 0, all we need to do is drop open sorts.
 */
static void
initialize_phase(AggState *aggstate, int newphase)
{
	Assert(newphase <= 1 || newphase == aggstate->current_phase + 1);

	/*
	 * Whatever the previous state, we're now done with whatever input
	 * tuplesort was in use.
	 */
	if (aggstate->sort_in)
	{
		tuplesort_end(aggstate->sort_in);
		aggstate->sort_in = NULL;
	}

	if (newphase <= 1)
	{
		/*
		 * Discard any existing output tuplesort.
		 */
		if (aggstate->sort_out)
		{
			tuplesort_end(aggstate->sort_out);
			aggstate->sort_out = NULL;
		}
	}
	else
	{
		/*
		 * The old output tuplesort becomes the new input one, and this is the
		 * right time to actually sort it.
		 */
		aggstate->sort_in = aggstate->sort_out;
		aggstate->sort_out = NULL;
		Assert(aggstate->sort_in);
		tuplesort_performsort(aggstate->sort_in);
	}

	/*
	 * If this isn't the last phase, we need to sort appropriately for the
	 * next phase in sequence.
	 */
	if (newphase > 0 && newphase < aggstate->numphases - 1)
	{
		Sort	   *sortnode = aggstate->phases[newphase + 1].sortnode;
		PlanState  *outerNode = outerPlanState(aggstate);
		TupleDesc	tupDesc = ExecGetResultType(outerNode);

		aggstate->sort_out = tuplesort_begin_heap(tupDesc,
												  sortnode->numCols,
												  sortnode->sortColIdx,
												  sortnode->sortOperators,
												  sortnode->collations,
												  sortnode->nullsFirst,
												  PlanStateOperatorMemKB((PlanState *) aggstate),
												  NULL, false);
	}