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, 19 insertions, 0 deletions

diff --git a/src/backend/utils/adt/timestamp.c b/src/backend/utils/adt/timestamp.c
index 6fa126d295b..b11d452fc8a 100644
--- a/src/backend/utils/adt/timestamp.c
+++ b/src/backend/utils/adt/timestamp.c
@@ -2113,6 +2113,11 @@ timestamp_hash(PG_FUNCTION_ARGS)
 	return hashint8(fcinfo);
 }
 
+Datum
+timestamp_hash_extended(PG_FUNCTION_ARGS)
+{
+	return hashint8extended(fcinfo);
+}
 
 /*
  * Cross-type comparison functions for timestamp vs timestamptz
@@ -2419,6 +2424,20 @@ interval_hash(PG_FUNCTION_ARGS)
 	return DirectFunctionCall1(hashint8, Int64GetDatumFast(span64));
 }
 
+Datum
+interval_hash_extended(PG_FUNCTION_ARGS)
+{
+	Interval   *interval = PG_GETARG_INTERVAL_P(0);
+	INT128		span = interval_cmp_value(interval);
+	int64		span64;
+
+	/* Same approach as interval_hash */
+	span64 = int128_to_int64(span);
+
+	return DirectFunctionCall2(hashint8extended, Int64GetDatumFast(span64),
+							   PG_GETARG_DATUM(1));
+}
+
 /* overlaps_timestamp() --- implements the SQL OVERLAPS operator.
  *
  * Algorithm is per SQL spec.  This is much harder than you'd think