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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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79
src/backend/utils/adt/arrayfuncs.c
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@ -20,6 +20,7 @@
#endif
#include <math.h>
#include "access/hash.h"
#include "access/htup_details.h"
#include "catalog/pg_type.h"
#include "funcapi.h"
@ -4020,6 +4021,84 @@ hash_array(PG_FUNCTION_ARGS)
PG_RETURN_UINT32(result);
}
/*
* Returns 64-bit value by hashing a value to a 64-bit value, with a seed.
* Otherwise, similar to hash_array.
*/
Datum
hash_array_extended(PG_FUNCTION_ARGS)
{
AnyArrayType *array = PG_GETARG_ANY_ARRAY(0);
uint64 seed = PG_GETARG_INT64(1);
int ndims = AARR_NDIM(array);
int *dims = AARR_DIMS(array);
Oid element_type = AARR_ELEMTYPE(array);
uint64 result = 1;
int nitems;
TypeCacheEntry *typentry;
int typlen;
bool typbyval;
char typalign;
int i;
array_iter iter;
FunctionCallInfoData locfcinfo;
typentry = (TypeCacheEntry *) fcinfo->flinfo->fn_extra;
if (typentry == NULL ||
typentry->type_id != element_type)
{
typentry = lookup_type_cache(element_type,
TYPECACHE_HASH_EXTENDED_PROC_FINFO);
if (!OidIsValid(typentry->hash_extended_proc_finfo.fn_oid))
ereport(ERROR,
(errcode(ERRCODE_UNDEFINED_FUNCTION),
errmsg("could not identify an extended hash function for type %s",
format_type_be(element_type))));
fcinfo->flinfo->fn_extra = (void *) typentry;
}
typlen = typentry->typlen;
typbyval = typentry->typbyval;
typalign = typentry->typalign;
InitFunctionCallInfoData(locfcinfo, &typentry->hash_extended_proc_finfo, 2,
InvalidOid, NULL, NULL);
/* Loop over source data */
nitems = ArrayGetNItems(ndims, dims);
array_iter_setup(&iter, array);
for (i = 0; i < nitems; i++)
{
Datum elt;
bool isnull;
uint64 elthash;
/* Get element, checking for NULL */
elt = array_iter_next(&iter, &isnull, i, typlen, typbyval, typalign);
if (isnull)
{
elthash = 0;
}
else
{
/* Apply the hash function */
locfcinfo.arg[0] = elt;
locfcinfo.arg[1] = seed;
locfcinfo.argnull[0] = false;
locfcinfo.argnull[1] = false;
locfcinfo.isnull = false;
elthash = DatumGetUInt64(FunctionCallInvoke(&locfcinfo));
}
result = (result << 5) - result + elthash;
}
AARR_FREE_IF_COPY(array, 0);
PG_RETURN_UINT64(result);
}
/*-----------------------------------------------------------------------------
* array overlap/containment comparisons