Horton

Re: ALTER tbl rewrite loses CLUSTER ON index (consider moving indisclustered to pg_class)

Amit Langote <amitlangote09@gmail.com>

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From: Amit Langote <amitlangote09@gmail.com>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2020-02-17T05:31:42Z
Lists: pgsql-hackers 
Hi Justin,

On Fri, Feb 7, 2020 at 11:39 PM Justin Pryzby <pryzby@telsasoft.com> wrote:
> On Thu, Feb 06, 2020 at 02:24:47PM -0300, Alvaro Herrera wrote:
> > On 2020-Feb-06, Justin Pryzby wrote:
> >
> > > I wondered if it wouldn't be better if CLUSTER ON was stored in pg_class as the
> > > Oid of a clustered index, rather than a boolean in pg_index.
> >
> > Maybe.  Do you want to try a patch?
>
> I think the attached is 80% complete (I didn't touch pg_dump).
>
> One objection to this change would be that all relations (including indices)
> end up with relclustered fields, and pg_index already has a number of bools, so
> it's not like this one bool is wasting a byte.
>
> I think relisclustered was a's clever way of avoiding that overhead (c0ad5953).
> So I would be -0.5 on moving it to pg_class..

Are you still for fixing ALTER TABLE losing relisclustered with the
patch we were working on earlier [1], if not for moving relisclustered
to pg_class anymore?

I have read elsewhere [2] that forcing ALTER TABLE to rewrite in
clustered order might not be a good option, but maybe that one is a
more radical proposal than this.

Thanks,
Amit

[1] https://postgr.es/m/CA%2BHiwqEt1HnXYckCdaO8%2BpOoFs7NNS5byoZ6Xg2B7epKbhS85w%40mail.gmail.com
[2] https://postgr.es/m/10984.1581181029%40sss.pgh.pa.us

Commits

  1. Refactor cluster.c to use new routine get_index_isclustered()

  2. Preserve clustered index after rewrites with ALTER TABLE

  3. Preserve replica identity index across ALTER TABLE rewrite

  4. Remove RangeIOData->typiofunc

  5. Preserve pg_index.indisclustered across REINDEX CONCURRENTLY