Re: Logical Replication of sequences

On Fri, 7 Nov 2025 at 14:54, shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> On Fri, Nov 7, 2025 at 10:58 AM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> >
> >
> > Thanks for pushing the patch, here is a rebased version of the
> > remaining patches.
> >
>
> Please find a few comments on doc patch:
>
> 1)
> + them. To verify this, compare the
> + <link linkend="catalog-pg-subscription-rel">pg_subscription_rel</link>.<structfield>srsublsn</structfield>
> + on the subscriber with the page_lsn obtained from the
> + <function>pg_get_sequence_data</function> for the sequence on the
> publisher.
>
> Is there a way to give link of 'pg_get_sequence_data' here?

Modified

> 2)
> + <warning>
> + <para>
> + Each sequence caches a block of values (typically 32) in memory before
> + generating a new WAL record, so its LSN advances only after the entire
> + cached batch has been consumed. As a result, sequence value
> drift cannot be
> + detected by comparing LSNs for sequence increments that fall within the
> + same cached block.
> + </para>
> + </warning>
>
> In such a case, shall we mention that compare last_value to see the
> drift? Thoughts?

I was not sure as it might not be very efficient

> 3)
>
> + To detect this, compare the
> + <link linkend="catalog-pg-subscription-rel">pg_subscription_rel</link>.<structfield>srsublsn</structfield>
> + on the subscriber with the page_lsn obtained from the
> + <function>pg_get_sequence_data</function> for the sequence on the
> publisher.
>
>
> We have mentioned above. But in the example of the same, we do not
> show srsublsn or page_lsn anywhere. Shall we query and show that as
> well?

Updated example

>
> 4)
> Maximum number of synchronization workers per subscription. This
> parameter controls the amount of parallelism of the initial data copy
> during the subscription initialization or when new tables are added.
> + One additional worker is also needed for sequence synchronization.
> </para>
>
> Since now the first line is talking only about table-sync, shall we tweak it:
> 'of the initial data copy' --> 'of the initial data copy for tables'

Modified

> 5)
> + Returns information about the sequence. <literal>last_value</literal>
> + indicates last sequence value set in sequence by nextval or setval,
>
> last_value can also be set by seq synchronization. Do you think that
> we need to mention that or current info is good enough?

Updated

The attached v20251107_2 version patch has the changes for the same.

Regards,
Vignesh