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

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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
This commit is contained in:
Robert Haas
2017-08-31 22:21:21 -04:00
parent 2d44c58c79
commit 81c5e46c49
33 changed files with 1555 additions and 42 deletions
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21
src/backend/utils/adt/date.c
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@@ -1508,6 +1508,12 @@ time_hash(PG_FUNCTION_ARGS)
return hashint8(fcinfo);
}
Datum
time_hash_extended(PG_FUNCTION_ARGS)
{
return hashint8extended(fcinfo);
}
Datum
time_larger(PG_FUNCTION_ARGS)
{
@@ -2213,6 +2219,21 @@ timetz_hash(PG_FUNCTION_ARGS)
PG_RETURN_UINT32(thash);
}
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)
{