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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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15
src/backend/utils/adt/acl.c
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@@ -16,6 +16,7 @@
#include <ctype.h>
#include "access/hash.h"
#include "access/htup_details.h"
#include "catalog/catalog.h"
#include "catalog/namespace.h"
@@ -717,6 +718,20 @@ hash_aclitem(PG_FUNCTION_ARGS)
PG_RETURN_UINT32((uint32) (a->ai_privs + a->ai_grantee + a->ai_grantor));
}
/*
* 64-bit hash function for aclitem.
*
* Similar to hash_aclitem, but accepts a seed and returns a uint64 value.
*/
Datum
hash_aclitem_extended(PG_FUNCTION_ARGS)
{
AclItem *a = PG_GETARG_ACLITEM_P(0);
uint64 seed = PG_GETARG_INT64(1);
uint32 sum = (uint32) (a->ai_privs + a->ai_grantee + a->ai_grantor);
return (seed == 0) ? UInt64GetDatum(sum) : hash_uint32_extended(sum, seed);
}
/*
* acldefault() --- create an ACL describing default access permissions