Re: [Patch] Omit virtual generated columns from test_decoding output

Hi,

On Mon, Aug 17, 2026 at 2:54 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> I agree with the proposed change. It's quite confusing to distinguish
> between a genuine NULL value and a NULL value in a virtual generated
> column, as Bharath mentioned.
>
> Here are some review comments:

Thanks for reviewing.

> +-- Check that virtual generated columns are omitted from the output (their
> +-- values are not stored on disk so heap_getattr() would otherwise emit a
> +-- wrong NULL), while stored generated columns are emitted normally.
>
> How about rewriting it to:
>
> +-- Virtual generated columns are always stored as null in the tuple, so they
> +-- are not printed at all; a printed null would not be distinguishable from a
> +-- column that really contains a null. Stored generated columns are printed
> +-- as usual.

Looks better. Used that.

> A similar change would be required to the comments in test_decoding.c.

Changed.

> ---
> +-- table with only virtual generated columns alongside the key
> +CREATE TABLE gtest2 (
> + a int PRIMARY KEY,
> + b int GENERATED ALWAYS AS (a + 1) VIRTUAL,
> + c text GENERATED ALWAYS AS ('row-' || a::text) VIRTUAL
> +);
> +INSERT INTO gtest2 (a) VALUES (10), (20);
> +SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,
> NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
>
> I don't think this test is needed as it doesn't improve test coverages.

Makes sense. I added a null column to the one test that we are left with.

> ---
> As for backpatching, IIUC it's not a correctness bug nor causes a
> server crash or data corruption. Given it might affect the existing
> consumers using test_decoding, I think it should be only for HEAD.

Agreed.

Please have a look at the v5 patch.

--
Bharath Rupireddy
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