Function ExecHashGetSkewBucket

src/backend/executor/nodeHash.c:3077–3113

* ExecHashGetSkewBucket * * Returns the index of the skew bucket for this hashvalue, * or INVALID_SKEW_BUCKET_NO if the hashvalue is not * associated with any active skew bucket. */

 *		associated with any active skew bucket.
 */
int
ExecHashGetSkewBucket(HashJoinTable hashtable, uint32 hashvalue)
{
	int			bucket;

	/*
	 * Always return INVALID_SKEW_BUCKET_NO if not doing skew optimization (in
	 * particular, this happens after the initial batch is done).
	 */
	if (!hashtable->skewEnabled)
		return INVALID_SKEW_BUCKET_NO;

	/*
	 * Since skewBucketLen is a power of 2, we can do a modulo by ANDing.
	 */
	bucket = hashvalue & (hashtable->skewBucketLen - 1);

	/*
	 * While we have not hit a hole in the hashtable and have not hit the
	 * desired bucket, we have collided with some other hash value, so try the
	 * next bucket location.
	 */
	while (hashtable->skewBucket[bucket] != NULL &&
		   hashtable->skewBucket[bucket]->hashvalue != hashvalue)
		bucket = (bucket + 1) & (hashtable->skewBucketLen - 1);

	/*
	 * Found the desired bucket?
	 */
	if (hashtable->skewBucket[bucket] != NULL)
		return bucket;

	/*
	 * There must not be any hashtable entry for this hash value.
	 */
	return INVALID_SKEW_BUCKET_NO;
}

/*
 * ExecHashSkewTableInsert