Function get_partition_for_tuple

src/backend/executor/execPartition.c:1361–1572

* get_partition_for_tuple * Finds partition of relation which accepts the partition key specified * in values and isnull. * * Calling this function can be quite expensive when LIST and RANGE * partitioned tables have many partitions. This is due to the binary search * that's done to find the correct partition. Many of the use cases for LIST * and RANGE partitioned tables make it likely

 * found or -1 if none found.
 */
int
get_partition_for_tuple(PartitionKey key, PartitionDesc partdesc, Datum *values, bool *isnull)
{
	int			bound_offset = -1;
	int			part_index = -1;
	PartitionBoundInfo boundinfo = partdesc->boundinfo;

	if (partdesc->nparts == 0)
		return part_index;
	/*
	 * In the switch statement below, when we perform a cached lookup for
	 * RANGE and LIST partitioned tables, if we find that the last found
	 * partition matches the 'values', we return the partition index right
	 * away.  We do this instead of breaking out of the switch as we don't
	 * want to execute the code about the DEFAULT partition or do any updates
	 * for any of the cache-related fields.  That would be a waste of effort
	 * as we already know it's not the DEFAULT partition and have no need to
	 * increment the number of times we found the same partition any higher
	 * than PARTITION_CACHED_FIND_THRESHOLD.
	 */

	/* Route as appropriate based on partitioning strategy. */
	switch (key->strategy)
	{
		case PARTITION_STRATEGY_HASH:
			{
				uint64		rowHash;

				/* hash partitioning is too cheap to bother caching */
				rowHash = compute_partition_hash_value(key->partnatts,
													   key->partsupfunc,
													   key->partcollation,
													   values, isnull);

				/*
				 * HASH partitions can't have a DEFAULT partition and we don't
				 * do any caching work for them, so just return the part index
				 */
				return boundinfo->indexes[rowHash % boundinfo->nindexes];
			}

		case PARTITION_STRATEGY_LIST:
			if (isnull[0])
			{
				/* this is far too cheap to bother doing any caching */
				if (partition_bound_accepts_nulls(boundinfo))
				{
					/*
					 * When there is a NULL partition we just return that
					 * directly.  We don't have a bound_offset so it's not
					 * valid to drop into the code after the switch which
					 * checks and updates the cache fields.  We perhaps should
					 * be invalidating the details of the last cached
					 * partition but there's no real need to.  Keeping those
					 * fields set gives a chance at matching to the cached
					 * partition on the next lookup.
					 */
					return boundinfo->null_index;