Function ExecAgg

src/backend/executor/nodeAgg.c:2336–2374

* ExecAgg - * * ExecAgg receives tuples from its outer subplan and aggregates over * the appropriate attribute for each aggregate function use (Aggref * node) appearing in the targetlist or qual of the node. The number * of tuples to aggregate over depends on whether grouped or plain * aggregation is selected. In grouped aggregation, we produce a result * row for each group; i

 * Streaming: forces not spilling, roughly deduplicates to save network I/O.
 */
static TupleTableSlot *
ExecAgg(PlanState *pstate)
{
	AggState   *node = castNode(AggState, pstate);
	TupleTableSlot *result = NULL;

	CHECK_FOR_INTERRUPTS();

	if (!node->agg_done)
	{
		/* Dispatch based on strategy */
		switch (node->phase->aggstrategy)
		{
			case AGG_HASHED:
				if (!node->table_filled)
					agg_fill_hash_table(node);
				/* FALLTHROUGH */
			case AGG_MIXED:
				result = agg_retrieve_hash_table(node);
				break;
			case AGG_PLAIN:
			case AGG_SORTED:
				result = agg_retrieve_direct(node);
				break;
		}

		if (!TupIsNull(result))
			return result;
	}

	/* Save statistics into the cdbexplainbuf for EXPLAIN ANALYZE */
	if (node->ss.ps.instrument &&
			(node->ss.ps.instrument)->need_cdb &&
			(node->phase->aggstrategy == AGG_HASHED ||
			node->phase->aggstrategy == AGG_MIXED))
		agg_hash_explain_extra_message(node);

	return NULL;
}

/*
 * ExecAgg for non-hashed case