Re: Fast, stable, portable hash function producing 4-byte or 8-byte values?

On Tue, 2019-12-10 at 22:11 +0100, Erwin Brandstetter wrote:
> I am looking for stable hash functions producing 8-byte or 4-byte hashes from long text values in Postgres 10 or later.
> 
> [...]
>
> There is an old post from 2012 by Tom Lane suggesting that hashtext() and friends are not for users:
> 
> https://www.postgresql.org/message-id/24463.1329854466%40sss.pgh.pa.us

Changing a hash function would corrupt hash indexes, wouldn't it?

So I'd expect these functions to be pretty stable:

SELECT amp.amproc
FROM pg_amproc AS amp
   JOIN pg_opfamily AS opf ON amp.amprocfamily = opf.oid
   JOIN pg_am ON opf.opfmethod = pg_am.oid
WHERE pg_am.amname = 'hash'
  AND amp.amprocnum = 1;

Or at least there would have to be a fat warning in the release notes
to reindex hash indexes.

Yours,
Laurenz Albe
-- 
Cybertec | https://www.cybertec-postgresql.com