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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: Postgres hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: REINDEX INDEX results in a crash for an index of pg_class since 9.6
Date: Wed, 01 May 2019 19:41:24 -0400
Message-ID: <16043.1556754084@sss.pgh.pa.us> (raw)
In-Reply-To: <5483.1556737736@sss.pgh.pa.us>
References: <16277.1556649660@sss.pgh.pa.us>
	<20190430190308.kga2z5oz7vab7w22@alap3.anarazel.de>
	<17996.1556651503@sss.pgh.pa.us>
	<20190430221045.6slpi2vm2noda5jb@alap3.anarazel.de>
	<28313.1556663080@sss.pgh.pa.us>
	<28926.1556664156@sss.pgh.pa.us>
	<20190430225307.lvfvcf2776iywhw4@alap3.anarazel.de>
	<20190501013638.7u7fwr4zktbyyng5@alap3.anarazel.de>
	<25049.1556727622@sss.pgh.pa.us>
	<20190501170603.hx6r3ztyvi3rlgq6@alap3.anarazel.de>
	<20190501172115.4cvz3rp6np43odut@alap3.anarazel.de>
	<5483.1556737736@sss.pgh.pa.us>

I wrote:
> Andres Freund <andres@anarazel.de> writes:
>> On 2019-05-01 10:06:03 -0700, Andres Freund wrote:
>>> I'm not sure this is the right short-term answer. Why isn't it, for now,
>>> sufficient to do what I suggested with RelationSetNewRelfilenode() not
>>> doing the CommandCounterIncrement(), and reindex_index() then doing the
>>> SetReindexProcessing() before a CommandCounterIncrement()? That's like
>>> ~10 line code change, and a few more with comments.

> That looks like a hack to me...

> The main thing I'm worried about right now is that I realized that
> our recovery from errors in this area is completely hosed, cf
> https://www.postgresql.org/message-id/4541.1556736252@sss.pgh.pa.us

OK, so per the other thread, it seems like the error recovery problem
isn't going to affect this directly.  However, I still don't like this
proposal much; the reason being that it's a rather fundamental change
in the API of RelationSetNewRelfilenode.  This will certainly break
any external callers of that function --- and silently, too.

Admittedly, there might not be any outside callers, but I don't really
like that assumption for something we're going to have to back-patch.

The solution I'm thinking of should have much more localized effects,
basically just in reindex_index and RelationSetNewRelfilenode, which is
why I like it better.

			regards, tom lane





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  Cc: tgl@sss.pgh.pa.us, andres@anarazel.de, michael@paquier.xyz, pgsql-hackers@lists.postgresql.org
  Subject: Re: REINDEX INDEX results in a crash for an index of pg_class since 9.6
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