Re: [HACKERS] Hash Functions

Hi,

On 2017-08-03 17:43:44 -0400, Robert Haas wrote:
> For me, the basic point here is that we need a set of hash functions
> for hash partitioning that are different than what we use for hash
> indexes and hash joins -- otherwise when we hash partition a table and
> create hash indexes on each partition, those indexes will have nasty
> clustering.  Partitionwise hash joins will have similar problems.  So,
> a new set of hash functions specifically for hash partitioning is
> quite desirable.

Couldn't that just as well solved by being a bit smarter with an IV? I
doubt we want to end up with different hashfunctions for sharding,
partitioning, hashjoins (which seems to form a hierarchy). Having a
working hash-combine function, or even better a hash API that can
continue to use the hash's internal state, seems a more scalable
solution.

Greetings,

Andres Freund