Function perform_distinct_windowaggregate

src/backend/executor/nodeWindowAgg.c:677–750

* Call transition function for a DISTINCT-qualified aggregate. * * All the input values have been loaded into the tuplesort. Perform the sort, * deduplicate, and call the transition function for each unique value. */

 * deduplicate, and call the transition function for each unique value.
 */
static void
perform_distinct_windowaggregate(WindowAggState *winstate,
								 WindowStatePerFunc perfuncstate,
								 WindowStatePerAgg peraggstate)
{
	LOCAL_FCINFO(fcinfo, FUNC_MAX_ARGS);
	Datum		prevDatum = (Datum) 0;
	bool		prevNull = true;
	MemoryContext oldcontext;

	oldcontext = MemoryContextSwitchTo(winstate->tmpcontext->ecxt_per_tuple_memory);

	tuplesort_performsort(peraggstate->distinctSortState);

#ifdef FAULT_INJECTOR
	/*
	 * This routine is used for tracing whether the sort operation of DISTINCT-qualified
	 * WindowAgg spills to disk.
	 */
	if (SIMPLE_FAULT_INJECTOR("distinct_winagg_perform_sort") == FaultInjectorTypeSkip)
	{
		TuplesortInstrumentation sortstats;
		tuplesort_get_stats(peraggstate->distinctSortState, &sortstats);
		if (sortstats.spaceType == SORT_SPACE_TYPE_MEMORY)
			ereport(NOTICE,
					(errmsg("distinct winagg sortstats: sort operation fitted in memory")));
		else
			ereport(NOTICE,
					(errmsg("distinct winagg sortstats: sort operation spilled to disk")));
	}
#endif

	/* load the first tuple from spool */
	if (tuplesort_getdatum(peraggstate->distinctSortState, true,
						   &fcinfo->args[1].value, &fcinfo->args[1].isnull, NULL))
	{
		call_transfunc(winstate, perfuncstate, peraggstate, fcinfo);
		prevDatum = fcinfo->args[1].value;
		prevNull = fcinfo->args[1].isnull;

		/* continue loading more tuples */
		while (tuplesort_getdatum(peraggstate->distinctSortState, true,
								  &fcinfo->args[1].value, &fcinfo->args[1].isnull, NULL))
		{
			int		cmp;

			cmp = ApplySortComparator(prevDatum, prevNull,
									  fcinfo->args[1].value, fcinfo->args[1].isnull,
									  &peraggstate->distinctComparator);
			if (cmp < 0)
			{
				call_transfunc(winstate, perfuncstate, peraggstate, fcinfo);
			}
			else if (cmp == 0)
			{
				/* Equal, skip it */
			}
			else