From: Antonin Houska <ah@cybertec.at>
To: Ewan Young <kdbase.hack@gmail.com>
cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
    mihailnikalayeu@gmail.com, alvherre@kurilemu.de
Subject: Re: REPACK CONCURRENTLY fails on tables with generated columns
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Comments: In-reply-to Ewan Young <kdbase.hack@gmail.com>
   message dated "Fri, 12 Jun 2026 16:39:54 +0800."
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Date: Fri, 12 Jun 2026 11:52:12 +0200
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Ewan Young <kdbase.hack@gmail.com> wrote:

> REPACK (CONCURRENTLY) aborts with an internal error on any table that has
> a STORED generated column, if a concurrent UPDATE that requires index
> maintenance is applied during the catch-up phase:
> 
> ERROR:  no generation expression found for column number 3 of table
> "pg_temp_16396"
> Plain (non-concurrent) REPACK on such a table works fine, and so does
> REPACK (CONCURRENTLY) as long as no qualifying concurrent change is
> applied -- so the problem is specific to the concurrent-change apply path.

Thanks for the report!

> The attached patch adds an isolation test, but here is the manual
> sequence (server built with --enable-injection-points):
> 
> CREATE EXTENSION injection_points;
> CREATE TABLE t (i int PRIMARY KEY, v int,
>                 g int GENERATED ALWAYS AS (v * 10) STORED);
> CREATE INDEX ON t (v);              -- makes UPDATE of v non-HOT
> INSERT INTO t(i, v) VALUES (1, 1);
> 
> -- session 1:
> SELECT injection_points_attach('repack-concurrently-before-lock', 'wait');
> REPACK (CONCURRENTLY) t;            -- blocks at the injection point
> 
> -- session 2, once session 1 is waiting:
> UPDATE t SET v = v + 1 WHERE i = 1;
> SELECT injection_points_wakeup('repack-concurrently-before-lock');
> 
> -- session 1 then fails with the ERROR above.

I confirm I can reproduce it. I'll post a fix next week.

-- 
Antonin Houska
Web: https://www.cybertec-postgresql.com