Re: Logical Replication of sequences

On Tue, 20 Jan 2026 at 09:47, Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Mon, Jan 19, 2026 at 6:36 PM vignesh C <vignesh21@gmail.com> wrote:
> >
> > pg_get_sequence_data() internally uses try_relation_open() rather than
> > relation_open(). As a result, if the target sequence no longer exists
> > at the time of access, the function does not raise an error and
> > instead returns NULLs for the sequence state columns. The sequence
> > sync worker code previously assumed these columns to be non NULL and
> > asserted accordingly. This assumption does not hold in the presence of
> > concurrent DDL. The patch updates the sequence sync logic to
> > explicitly check for NULL values returned from pg_get_sequence_data().
> > If any of the required sequence state fields are NULL, the sequence
> > sync worker skips processing that sequence to identify and report the
> > missing sequences. The attached patch has the changes for the same.
> >
>
> - seqinfo_local->last_value = DatumGetInt64(slot_getattr(slot, ++col, &isnull));
> - Assert(!isnull);
> + /*
> + * If the sequence was dropped concurrently, pg_get_sequence_data() can
> + * return NULLs.
> + */
> + datum = slot_getattr(slot, ++col, &isnull);
> + if (isnull)
> + return COPYSEQ_SKIPPED;
> + seqinfo_local->last_value = DatumGetInt64(datum);
>
> - seqinfo_local->is_called = DatumGetBool(slot_getattr(slot, ++col, &isnull));
> - Assert(!isnull);
> + datum = slot_getattr(slot, ++col, &isnull);
> + if (isnull)
> + return COPYSEQ_SKIPPED;
> + seqinfo_local->is_called = DatumGetBool(datum);
>
> Is there a case where the first one (last_value) is non-null but later
> can be null? If not, then I think it is better to retain assert for
> other cases.

That is not possible. Updated accordingly with slight change to
comment. The attached patch has the changes for the same.

Regards,
Vignesh