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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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19
src/backend/utils/adt/timestamp.c
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@ -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