Function agg_refill_hash_table

src/backend/executor/nodeAgg.c:2798–2942

* If any data was spilled during hash aggregation, reset the hash table and * reprocess one batch of spilled data. After reprocessing a batch, the hash * table will again contain data, ready to be consumed by * agg_retrieve_hash_table_in_memory(). * * Should only be called after all in memory hash table entries have been * finalized and emitted. * * Return false when input is exhausted and

 * otherwise return true.
 */
static bool
agg_refill_hash_table(AggState *aggstate)
{
	HashAggBatch *batch;
	AggStatePerHash perhash;
	HashAggSpill spill;
	HashTapeInfo *tapeinfo = aggstate->hash_tapeinfo;
	bool		spill_initialized = false;

	if (aggstate->hash_batches == NIL)
		return false;

	/* hash_batches is a stack, with the top item at the end of the list */
	batch = llast(aggstate->hash_batches);
	aggstate->hash_batches = list_delete_last(aggstate->hash_batches);

	hash_agg_set_limits(aggstate, aggstate->hashentrysize, batch->input_card,
						batch->used_bits, &aggstate->hash_mem_limit,
						&aggstate->hash_ngroups_limit, NULL);

	/*
	 * Each batch only processes one grouping set; set the rest to NULL so
	 * that advance_aggregates() knows to ignore them. We don't touch
	 * pergroups for sorted grouping sets here, because they will be needed if
	 * we rescan later. The expressions for sorted grouping sets will not be
	 * evaluated after we recompile anyway.
	 */
	MemSet(aggstate->hash_pergroup, 0,
		   sizeof(AggStatePerGroup) * aggstate->num_hashes);

	/* free memory and reset hash tables */
	ReScanExprContext(aggstate->hashcontext);
	for (int setno = 0; setno < aggstate->num_hashes; setno++)
		ResetTupleHashTable(aggstate->perhash[setno].hashtable);

	aggstate->hash_ngroups_current = 0;

	/*
	 * In AGG_MIXED mode, hash aggregation happens in phase 1 and the output
	 * happens in phase 0. So, we switch to phase 1 when processing a batch,
	 * and back to phase 0 after the batch is done.
	 */
	Assert(aggstate->current_phase == 0);
	if (aggstate->phase->aggstrategy == AGG_MIXED)
	{
		aggstate->current_phase = 1;
		aggstate->phase = &aggstate->phases[aggstate->current_phase];
	}

	select_current_set(aggstate, batch->setno, true);

	perhash = &aggstate->perhash[aggstate->current_set];

	/*
	 * Spilled tuples are always read back as MinimalTuples, which may be
	 * different from the outer plan, so recompile the aggregate expressions.
	 *
	 * We still need the NULL check, because we are only processing one