Re: REPACK CONCURRENTLY fails on tables with generated columns

Ewan Young <kdbase(dot)hack(at)gmail(dot)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