Introduce 64-bit hash functions with a 64-bit seed.

This will be useful for hash partitioning, which needs a way to seed
the hash functions to avoid problems such as a hash index on a hash
partitioned table clumping all values into a small portion of the
bucket space; it's also useful for anything that wants a 64-bit hash
value rather than a 32-bit hash value.

Just in case somebody wants a 64-bit hash value that is compatible
with the existing 32-bit hash values, make the low 32-bits of the
64-bit hash value match the 32-bit hash value when the seed is 0.

Robert Haas and Amul Sul

Discussion: http://postgr.es/m/CA+Tgmoafx2yoJuhCQQOL5CocEi-w_uG4S2xT0EtgiJnPGcHW3g@mail.gmail.com

1 files changed, 21 insertions, 0 deletions

diff --git a/src/backend/utils/adt/date.c b/src/backend/utils/adt/date.c
index 7d89d794381..34c0b52d583 100644
--- a/src/backend/utils/adt/date.c
+++ b/src/backend/utils/adt/date.c
@@ -1509,6 +1509,12 @@ time_hash(PG_FUNCTION_ARGS)
 }
 
 Datum
+time_hash_extended(PG_FUNCTION_ARGS)
+{
+	return hashint8extended(fcinfo);
+}
+
+Datum
 time_larger(PG_FUNCTION_ARGS)
 {
 	TimeADT		time1 = PG_GETARG_TIMEADT(0);
@@ -2214,6 +2220,21 @@ timetz_hash(PG_FUNCTION_ARGS)
 }
 
 Datum
+timetz_hash_extended(PG_FUNCTION_ARGS)
+{
+	TimeTzADT  *key = PG_GETARG_TIMETZADT_P(0);
+	uint64		seed = PG_GETARG_DATUM(1);
+	uint64		thash;
+
+	/* Same approach as timetz_hash */
+	thash = DatumGetUInt64(DirectFunctionCall2(hashint8extended,
+											   Int64GetDatumFast(key->time),
+											   seed));
+	thash ^= DatumGetUInt64(hash_uint32_extended(key->zone, seed));
+	PG_RETURN_UINT64(thash);
+}
+
+Datum
 timetz_larger(PG_FUNCTION_ARGS)
 {
 	TimeTzADT  *time1 = PG_GETARG_TIMETZADT_P(0);