Date: Fri, 28 Feb 2020 20:42:02 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>,
	Amit Langote <amitlangote09@gmail.com>,
	pgsql-hackers@postgresql.org, Michael Paquier <michael@paquier.xyz>
Subject: Re: ALTER tbl rewrite loses CLUSTER ON index
Message-ID: <20200229024202.GH29456@telsasoft.com>
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 <20200207143935.GP403@telsasoft.com>
 <17937.1582932364@sss.pgh.pa.us>
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On Fri, Feb 28, 2020 at 06:26:04PM -0500, Tom Lane wrote:
> Justin Pryzby <pryzby@telsasoft.com> writes:
> > 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..
> > But I think 0001 and 0002 are worthy.  Maybe the test in 0002 should live
> > somewhere else.
> 
> 0001 has been superseded by events (faade5d4c), so the cfbot is choking
> on that one's failure to apply, and not testing any further.  Please
> repost without 0001 so that we can get this testing again.

I've just noticed while working on (1) that this separately affects REINDEX
CONCURRENTLY, which would be a new bug in v12.  Without CONCURRENTLY there's no
issue.  I guess we need a separate patch for that case.

(1) https://commitfest.postgresql.org/27/2269/

The ALTER bug goes back further and its fix should be a kept separate.

postgres=# DROP TABLE tt; CREATE TABLE tt(i int unique); CLUSTER tt USING tt_i_key; CLUSTER tt; REINDEX INDEX tt_i_key; CLUSTER tt;
DROP TABLE
CREATE TABLE
CLUSTER
CLUSTER
REINDEX
CLUSTER

postgres=# DROP TABLE tt; CREATE TABLE tt(i int unique); CLUSTER tt USING tt_i_key; CLUSTER tt; REINDEX INDEX CONCURRENTLY tt_i_key; CLUSTER tt;
DROP TABLE
CREATE TABLE
CLUSTER
CLUSTER
REINDEX
ERROR:  there is no previously clustered index for table "tt"

-- 
Justin