| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| 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 20:20:28 |
| Message-ID: | 20171012202028.oett7x232nbus4iv@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
On 2017-10-12 16:06:11 -0400, Robert Haas wrote:
> On Thu, Oct 12, 2017 at 3:43 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > Are we going to rely on the the combine function to stay the same
> > forever after?
>
> If we change them, it will be a pg_upgrade compatibility break for
> anyone using hash-partitioned tables with more than one partitioning
> column. Dump and reload will also break unless
> --load-via-partition-root is used.
>
> 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.
Greetings,
Andres Freund
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