ShardInterval *
FindShardInterval(Datum partitionColumnValue, CitusTableCacheEntry *cacheEntry)
{
	Datum searchedValue = partitionColumnValue;

	if (IsCitusTableTypeCacheEntry(cacheEntry, HASH_DISTRIBUTED))
	{
		searchedValue = FunctionCall1Coll(cacheEntry->hashFunction,
										  cacheEntry->partitionColumn->varcollid,
										  partitionColumnValue);
	}

	int shardIndex = FindShardIntervalIndex(searchedValue, cacheEntry);

	if (shardIndex == INVALID_SHARD_INDEX)
	{
		return NULL;
	}

	return cacheEntry->sortedShardIntervalArray[shardIndex];
}
…
int
CalculateUniformHashRangeIndex(int hashedValue, int shardCount)
{
	int64 hashedValue64 = (int64) hashedValue;

	/* normalize to the 0-UINT32_MAX range */
	int64 normalizedHashValue = hashedValue64 - PG_INT32_MIN;

	/* size of each hash range */
	int64 hashRangeSize = HASH_TOKEN_COUNT / shardCount;

	/* index of hash range into which the hash value falls */
	int shardIndex = (int) (normalizedHashValue / hashRangeSize);

	if (shardIndex < 0 || shardIndex > shardCount)
	{
		ereport(ERROR, (errmsg("bug: shard index %d out of bounds", shardIndex)));
	}

	/*
	 * If the shard count is not power of 2, the range of the last
	 * shard becomes larger than others. For that extra piece of range,
	 * we still need to use the last shard.
	 */
	if (shardIndex == shardCount)
	{
		shardIndex = shardCount - 1;
	}

	return shardIndex;
}

Échauffement