Function cdbhash

src/backend/cdb/cdbhash.c:188–247

* Add an attribute to the CdbHash calculation. * * Note: this must be called for each attribute, in order. If you try to hash * the attributes in a different order, you get a different hash value. */

 * the attributes in a different order, you get a different hash value.
 */
void
cdbhash(CdbHash *h, int attno, Datum datum, bool isnull)
{
	uint32		hashkey = h->hash;

	if (!h->is_legacy_hash)
	{
		/* rotate hashkey left 1 bit at each step */
		hashkey = (hashkey << 1) | ((hashkey & 0x80000000) ? 1 : 0);

		if (!isnull)
		{
			LOCAL_FCINFO(fcinfo, 1);
			uint32		hkey;

			InitFunctionCallInfoData(*fcinfo, &h->hashfuncs[attno - 1], 1,
									 DEFAULT_COLLATION_OID, /* have to specify collation for attribute of text or bpchar */
									 NULL, NULL);

			fcinfo->args[0].value = datum;
			fcinfo->args[0].isnull = false;

			hkey = DatumGetUInt32(FunctionCallInvoke(fcinfo));

			/* Check for null result, since caller is clearly not expecting one */
			if (fcinfo->isnull)
				elog(ERROR, "function %u returned NULL", fcinfo->flinfo->fn_oid);

			hashkey ^= hkey;
		}
	}
	else
	{
		magic_hash_stash = hashkey;
		if (!isnull)
		{
			LOCAL_FCINFO(fcinfo, 1);
			uint32		hkey;

			InitFunctionCallInfoData(*fcinfo, &h->hashfuncs[attno - 1], 1,
									 DEFAULT_COLLATION_OID, /* legacy hash functions don't care about collations */
									 NULL, NULL);

			fcinfo->args[0].value = datum;
			fcinfo->args[0].isnull = false;

			hkey = DatumGetUInt32(FunctionCallInvoke(fcinfo));

			/* Check for null result, since caller is clearly not expecting one */
			if (fcinfo->isnull)
				elog(ERROR, "function %u returned NULL", fcinfo->flinfo->fn_oid);

			hashkey = hkey;
		}
		else
			hashkey = cdblegacyhash_null();
		magic_hash_stash = FNV1_32_INIT;
	}