Function hashagg_spill_tuple

src/backend/executor/nodeAgg.c:3245–3304

* hashagg_spill_tuple * * No room for new groups in the hash table. Save for later in the appropriate * partition. */

 * partition.
 */
static Size
hashagg_spill_tuple(AggState *aggstate, HashAggSpill *spill,
					TupleTableSlot *inputslot, uint32 hash)
{
	LogicalTapeSet *tapeset = spill->tapeset;
	TupleTableSlot *spillslot;
	int			partition;
	MinimalTuple tuple;
	int			tapenum;
	int			total_written = 0;
	bool		shouldFree;

	Assert(spill->partitions != NULL);

	/* spill only attributes that we actually need */
	if (!aggstate->all_cols_needed)
	{
		spillslot = aggstate->hash_spill_wslot;
		slot_getsomeattrs(inputslot, aggstate->max_colno_needed);
		ExecClearTuple(spillslot);
		for (int i = 0; i < spillslot->tts_tupleDescriptor->natts; i++)
		{
			if (bms_is_member(i + 1, aggstate->colnos_needed))
			{
				spillslot->tts_values[i] = inputslot->tts_values[i];
				spillslot->tts_isnull[i] = inputslot->tts_isnull[i];
			}
			else
				spillslot->tts_isnull[i] = true;
		}
		ExecStoreVirtualTuple(spillslot);
	}
	else
		spillslot = inputslot;

	tuple = ExecFetchSlotMinimalTuple(spillslot, &shouldFree);

	partition = (hash & spill->mask) >> spill->shift;
	spill->ntuples[partition]++;

	/*
	 * All hash values destined for a given partition have some bits in
	 * common, which causes bad HLL cardinality estimates. Hash the hash to
	 * get a more uniform distribution.
	 */
	addHyperLogLog(&spill->hll_card[partition], hash_bytes_uint32(hash));

	tapenum = spill->partitions[partition];

	LogicalTapeWrite(tapeset, tapenum, (void *) &hash, sizeof(uint32));
	total_written += sizeof(uint32);

	LogicalTapeWrite(tapeset, tapenum, (void *) tuple, tuple->t_len);
	total_written += tuple->t_len;

	if (shouldFree)
		pfree(tuple);