Function initialize_hash_entry

src/backend/executor/nodeAgg.c:2219–2251

* Initialize a freshly-created TupleHashEntry. */

 * Initialize a freshly-created TupleHashEntry.
 */
static void
initialize_hash_entry(AggState *aggstate, TupleHashTable hashtable,
					  TupleHashEntry entry)
{
	AggStatePerGroup pergroup;
	int			transno;

	aggstate->hash_ngroups_current++;
	hash_agg_check_limits(aggstate);

	/* no need to allocate or initialize per-group state */
	if (aggstate->numtrans == 0)
		return;

	pergroup = (AggStatePerGroup)
		MemoryContextAlloc(hashtable->tablecxt,
						   sizeof(AggStatePerGroupData) * aggstate->numtrans);

	entry->additional = pergroup;

	/*
	 * Initialize aggregates for new tuple group, lookup_hash_entries()
	 * already has selected the relevant grouping set.
	 */
	for (transno = 0; transno < aggstate->numtrans; transno++)
	{
		AggStatePerTrans pertrans = &aggstate->pertrans[transno];
		AggStatePerGroup pergroupstate = &pergroup[transno];
		if (!bms_is_member(transno, aggstate->aggs_used))
			continue;
		initialize_aggregate(aggstate, pertrans, pergroupstate);
	}
}

/*
 * Look up hash entries for the current tuple in all hashed grouping sets.