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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Alexandre Felipe <o.alexandre.felipe@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: BUG #19686: Rolling back SET TABLESPACE
Date: Tue, 29 Sep 2026 19:39:40 -0400
Message-ID: <714053.1790725180@sss.pgh.pa.us> (raw)
In-Reply-To: <lqlli2yiai6dimhlzm47qiwuiz3qczt7snhzkx6qvrmmbltw6w@i7pvrw556qwg>
References: <CAE8JnxP+Ubdj-kaxfgNt=3_FzD3GgOc3gEvPAvrXKfgTgH2q5w@mail.gmail.com>
	<lqlli2yiai6dimhlzm47qiwuiz3qczt7snhzkx6qvrmmbltw6w@i7pvrw556qwg>

Andres Freund <andres@anarazel.de> writes:
> I don't think copying the file at commit is a good path, we shouldn't make
> commits take arbitrarily long without pretty darn good reason. I don't think
> this is that.

+1.  Moving operations with a significant probability of failure into
COMMIT is also an anti-pattern.

> What about forcing indexes to be copied to a new relfilenode when copying the
> underlying table?

That seems like the logical solution to me.  Nobody will be surprised
if ALTER SET TABLESPACE takes a long time for a big table; at least
not if they understand that it requires copying the data somewhere
else.  Imposing costs at COMMIT time might well surprise people.

The one disadvantage I see is that (I imagine) a common use-case is
to move both a table and its indexes to a new tablespace, and this
solution will imply that that sequence double-copies the indexes.
Maybe it'd be worth providing a command variant that copies the
table and its indexes to a new tablespace in one step.  But that
is a future optimization, not part of the bug fix; and I could be
wrong about whether anyone even cares.

			regards, tom lane

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  Subject: Re: BUG #19686: Rolling back SET TABLESPACE
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