Function ExecHashIncreaseNumBuckets

src/backend/executor/nodeHash.c:1710–1771

* ExecHashIncreaseNumBuckets * increase the original number of buckets in order to reduce * number of tuples per bucket */

 *		number of tuples per bucket
 */
static void
ExecHashIncreaseNumBuckets(HashJoinTable hashtable)
{
	HashMemoryChunk chunk;

	/* do nothing if not an increase (it's called increase for a reason) */
	if (hashtable->nbuckets >= hashtable->nbuckets_optimal)
		return;

#ifdef HJDEBUG
	printf("Hashjoin %p: increasing nbuckets %d => %d\n",
		   hashtable, hashtable->nbuckets, hashtable->nbuckets_optimal);
#endif

	hashtable->nbuckets = hashtable->nbuckets_optimal;
	hashtable->log2_nbuckets = hashtable->log2_nbuckets_optimal;

	Assert(hashtable->nbuckets > 1);
	Assert(hashtable->nbuckets <= (INT_MAX / 2));
	Assert(hashtable->nbuckets == (1 << hashtable->log2_nbuckets));

	/*
	 * Just reallocate the proper number of buckets - we don't need to walk
	 * through them - we can walk the dense-allocated chunks (just like in
	 * ExecHashIncreaseNumBatches, but without all the copying into new
	 * chunks)
	 */
	hashtable->buckets.unshared =
		(HashJoinTuple *) repalloc(hashtable->buckets.unshared,
								   hashtable->nbuckets * sizeof(HashJoinTuple));

	memset(hashtable->buckets.unshared, 0,
		   hashtable->nbuckets * sizeof(HashJoinTuple));

	/* scan through all tuples in all chunks to rebuild the hash table */
	for (chunk = hashtable->chunks; chunk != NULL; chunk = chunk->next.unshared)
	{
		/* process all tuples stored in this chunk */
		size_t		idx = 0;

		while (idx < chunk->used)
		{
			HashJoinTuple hashTuple = (HashJoinTuple) (HASH_CHUNK_DATA(chunk) + idx);
			int			bucketno;
			int			batchno;

			ExecHashGetBucketAndBatch(hashtable, hashTuple->hashvalue,
									  &bucketno, &batchno);

			/* add the tuple to the proper bucket */
			hashTuple->next.unshared = hashtable->buckets.unshared[bucketno];
			hashtable->buckets.unshared[bucketno] = hashTuple;

			/* advance index past the tuple */
			idx += MAXALIGN(HJTUPLE_OVERHEAD +
							HJTUPLE_MINTUPLE(hashTuple)->t_len);
		}