Function create_agg_path

src/backend/optimizer/util/pathnode.c:5045–5101

* create_agg_path * Creates a pathnode that represents performing aggregation/grouping * * 'rel' is the parent relation associated with the result * 'subpath' is the path representing the source of data * 'target' is the PathTarget to be computed * 'aggstrategy' is the Agg node's basic implementation strategy * 'aggsplit' is the Agg node's aggregate-splitting mode * 'groupClause' is a li

 * 'numGroups' is the estimated number of groups (1 if not grouping)
 */
AggPath *
create_agg_path(PlannerInfo *root,
				RelOptInfo *rel,
				Path *subpath,
				PathTarget *target,
				AggStrategy aggstrategy,
				AggSplit aggsplit,
				bool streaming,
				List *groupClause,
				List *qual,
				const AggClauseCosts *aggcosts,
				double numGroups)
{
	AggPath    *pathnode = makeNode(AggPath);

	pathnode->path.pathtype = T_Agg;
	pathnode->path.parent = rel;
	pathnode->path.pathtarget = target;
	/* For now, assume we are above any joins, so no parameterization */
	pathnode->path.param_info = NULL;
	pathnode->path.parallel_aware = false;
	pathnode->path.parallel_safe = rel->consider_parallel &&
		subpath->parallel_safe;
	pathnode->path.parallel_workers = subpath->parallel_workers;
	if (aggstrategy == AGG_SORTED)
		pathnode->path.pathkeys = subpath->pathkeys;	/* preserves order */
	else
		pathnode->path.pathkeys = NIL;	/* output is unordered */
	pathnode->path.barrierHazard = subpath->barrierHazard;
	pathnode->subpath = subpath;
	pathnode->streaming = streaming;

	pathnode->aggstrategy = aggstrategy;
	pathnode->aggsplit = aggsplit;
	pathnode->numGroups = numGroups;
	pathnode->transitionSpace = aggcosts ? aggcosts->transitionSpace : 0;
	pathnode->groupClause = groupClause;
	pathnode->qual = qual;
	pathnode->path.motionHazard = subpath->motionHazard;
	pathnode->path.barrierHazard = subpath->barrierHazard;

	cost_agg(&pathnode->path, root,
			 aggstrategy, aggcosts,
			 list_length(groupClause), numGroups,
			 qual,
			 subpath->startup_cost, subpath->total_cost,
			 subpath->rows, subpath->pathtarget->width);

	/* add tlist eval cost for each output row */
	pathnode->path.startup_cost += target->cost.startup;
	pathnode->path.total_cost += target->cost.startup +
		target->cost.per_tuple * pathnode->path.rows;

	pathnode->path.locus = subpath->locus;

	return pathnode;
}