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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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43
src/backend/utils/adt/jsonb_op.c
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@ -291,3 +291,46 @@ jsonb_hash(PG_FUNCTION_ARGS)
PG_FREE_IF_COPY(jb, 0);
PG_RETURN_INT32(hash);
}
Datum
jsonb_hash_extended(PG_FUNCTION_ARGS)
{
Jsonb *jb = PG_GETARG_JSONB(0);
uint64 seed = PG_GETARG_INT64(1);
JsonbIterator *it;
JsonbValue v;
JsonbIteratorToken r;
uint64 hash = 0;
if (JB_ROOT_COUNT(jb) == 0)
PG_RETURN_UINT64(seed);
it = JsonbIteratorInit(&jb->root);
while ((r = JsonbIteratorNext(&it, &v, false)) != WJB_DONE)
{
switch (r)
{
/* Rotation is left to JsonbHashScalarValueExtended() */
case WJB_BEGIN_ARRAY:
hash ^= ((UINT64CONST(JB_FARRAY) << 32) | UINT64CONST(JB_FARRAY));
break;
case WJB_BEGIN_OBJECT:
hash ^= ((UINT64CONST(JB_FOBJECT) << 32) | UINT64CONST(JB_FOBJECT));
break;
case WJB_KEY:
case WJB_VALUE:
case WJB_ELEM:
JsonbHashScalarValueExtended(&v, &hash, seed);
break;
case WJB_END_ARRAY:
case WJB_END_OBJECT:
break;
default:
elog(ERROR, "invalid JsonbIteratorNext rc: %d", (int) r);
}
}
PG_FREE_IF_COPY(jb, 0);
PG_RETURN_UINT64(hash);
}