Function ExecParallelHashTuplePrealloc

src/backend/executor/nodeHash.c:4042–4092

* Increase the space preallocated in this backend for a given inner batch by * at least a given amount. This allows us to track whether a given batch * would fit in memory when loaded back in. Also increase the number of * batches or buckets if required. * * This maintains a running estimation of how much space will be taken when we * load the batch back into memory by simulating the way c

 * again.
 */
static bool
ExecParallelHashTuplePrealloc(HashJoinTable hashtable, int batchno, size_t size)
{
	ParallelHashJoinState *pstate = hashtable->parallel_state;
	ParallelHashJoinBatchAccessor *batch = &hashtable->batches[batchno];
	size_t		want = Max(size, HASH_CHUNK_SIZE - HASH_CHUNK_HEADER_SIZE);

	Assert(batchno > 0);
	Assert(batchno < hashtable->nbatch);
	Assert(size == MAXALIGN(size));

	LWLockAcquire(&pstate->lock, LW_EXCLUSIVE);

	/* Has another participant commanded us to help grow? */
	if (pstate->growth == PHJ_GROWTH_NEED_MORE_BATCHES ||
		pstate->growth == PHJ_GROWTH_NEED_MORE_BUCKETS)
	{
		ParallelHashGrowth growth = pstate->growth;

		LWLockRelease(&pstate->lock);
		if (growth == PHJ_GROWTH_NEED_MORE_BATCHES)
			ExecParallelHashIncreaseNumBatches(hashtable);
		else if (growth == PHJ_GROWTH_NEED_MORE_BUCKETS)
			ExecParallelHashIncreaseNumBuckets(hashtable);

		return false;
	}

	if (pstate->growth != PHJ_GROWTH_DISABLED &&
		batch->at_least_one_chunk &&
		(batch->shared->estimated_size + want + HASH_CHUNK_HEADER_SIZE
		 > pstate->space_allowed))
	{
		/*
		 * We have determined that this batch would exceed the space budget if
		 * loaded into memory.  Command all participants to help repartition.
		 */
		batch->shared->space_exhausted = true;
		pstate->growth = PHJ_GROWTH_NEED_MORE_BATCHES;
		LWLockRelease(&pstate->lock);

		return false;
	}

	batch->at_least_one_chunk = true;
	batch->shared->estimated_size += want + HASH_CHUNK_HEADER_SIZE;
	batch->preallocated = want;
	LWLockRelease(&pstate->lock);

	return true;
}

/*
 * Calculate the limit on how much memory can be used by Hash and similar