| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | amul sul <sulamul(at)gmail(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Thom Brown <thom(at)linux(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>, David Steele <david(at)pgmasters(dot)net>, Greg Stark <stark(at)mit(dot)edu>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [POC] hash partitioning |
| Date: | 2017-10-12 21:27:52 |
| Message-ID: | CA+Tgmoa-6z2kw_W6GP_-0jFOWu-3PVnyS4gC6-s=sPH4w0bhqg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Oct 12, 2017 at 4:20 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> In other words, it's not utterly fixed in stone --- we invented
>> --load-via-partition-root primarily to cope with circumstances that
>> could change hash values --- but we sure don't want to be changing it
>> with any regularity, or for a less-than-excellent reason.
>
> Yea, that's what I expected. It'd probably good for somebody to run
> smhasher or such on the output of the combine function (or even better,
> on both the 32 and 64 bit variants) in that case.
Not sure how that test suite works exactly, but presumably the
characteristics in practice will depend the behavior of the hash
functions used as input the combine function - so the behavior could
be good for an (int, int) key but bad for a (text, date) key, or
whatever.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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