Re: REPACK CONCURRENTLY fails on tables with generated columns

Thanks, Álvaro.

On Fri, Jul 3, 2026 at 7:12 PM Alvaro Herrera <alvherre(at)kurilemu(dot)de> wrote:
>
> Hello,
>
> On 2026-Jun-22, Ewan Young wrote:
>
> > I applied the patch and ran it through an injection-point reproducer
> > (cassert). Without the fix the bug reproduces (ERROR: no generation
> > expression found for column number 3 ...); with it, REPACK CONCURRENTLY
> > succeeds under a concurrent non-HOT UPDATE for a STORED generated column, an
> > index directly on the generated column, and a VIRTUAL column, with correct
> > values afterwards. Your repack.spec change passes.
> >
> > The approach is right and I've confirmed it fixes the bug, so +1 from me in
> > this direction.
>
> Cool, thanks for reviewing -- I have pushed this fix, with some
> stylistic changes and one bigger change: these catalog rows are only
> needed in concurrent mode, so there was no reason to copy them in the
> other case. So I restricted the copying to that case.
>
> I've been looking at the other proposed change, and I agree with it.
> Here's it, again with some style changes, and only one other proposed
> change: for setting up updatedCols, ignore dropped columns. I don't
> think this should change anything in practice, but it just feels wrong
> to claim that a dropped column is being changed by an update.

I read through the range-table change and it looks correct.

Agreed on skipping dropped columns — a dropped attribute can never be
an index key column, so its presence in updatedCols has no functional effect;
leaving it out is a pure clarity win.

Over-claiming "all columns updated" is the safe direction: it only
affects the btree
indexUnchanged / bottom-up-deletion hint, never correctness. And for the
concurrent-apply path losing that hint should rarely matter, so erring
this way looks right.

+1 to commit.

>
> --
> Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/

--
Regards,
Ewan Young