From: | Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> |
---|---|
To: | Erwin Brandstetter <brsaweda(at)gmail(dot)com>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: Fast, stable, portable hash function producing 4-byte or 8-byte values? |
Date: | 2019-12-10 22:13:23 |
Message-ID: | 67fe6aff570841a0fab4c7b9f5c316b5d54f88c3.camel@cybertec.at |
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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
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