Re: Logical Replication of sequences

On Tue, 15 Jul 2025 at 11:27, shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> Thank You. Few comments:
>
> 1)
> patch 005 has trailing whitespaces issue.

Fixed them

> 2)
> In LogicalRepSyncSequences(), do we really need this:
>
> + seq_count = list_length(subsequences);;
>
> seq_count is only used at the end to figure out if we really had some
> sequences. We can simply check subsequences against NIL for that
> purpose. If we really want to use list_length as a check, then we
> shall move it at the end where we use it.

Modified

> 3)
> LogicalRepSyncSequences():
> + MemoryContext oldctx;
>
> we can move this to a for-loop where it is being used.

Modified

> 4)
> The only usage of sequence_states_not_ready is this now:
>
> + /* No sequences to sync, so nothing to do */
> + if (list_length(sequence_states_not_ready) == 0)
> + return;
>
> Now, do we need to have it as a List?

Removed this list variable and used a output function argument in
FetchRelationStates

> 5)
> + <sect2 id="missing-sequences">
> + <title>Missing Sequences</title>
> + <para>
> + During sequence synchronization, if a sequence is dropped on the
> + publisher. An ERROR is logged listing the missing sequences before the
> + process exits. The apply worker detects this failure and repeatedly
> + respawns the sequence synchronization worker to continue the
> + synchronization process until the sequences are created in the publisher.
> + See also <link
> linkend="guc-wal-retrieve-retry-interval"><varname>wal_retrieve_retry_interval</varname></link>.
> + </para>
> + <para>
> + To resolve this, either use
> + <link linkend="sql-createsequence"><command>CREATE
> SEQUENCE</command></link>
> + to recreate the missing sequence on the publisher, or, if the sequence are
> + no longer required, execute <link
> linkend="sql-altersubscription-params-refresh-publication">
> + <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command></link>
> + to remove the stale sequence entries from synchronization in the
> subscriber.
> + </para>
> + </sect2>
> +
>
> Please see if this looks appropriate, I have added drop-sequence
> option as well and corrected few trivial things:
>
> During sequence synchronization, if a sequence is dropped on the
> publisher, an ERROR is logged listing the missing sequences before the
> process exits. The apply worker detects this failure and repeatedly
> respawns the sequence synchronization worker to continue the
> synchronization process until the sequences are either recreated on
> the publisher, dropped on the subscriber, or removed from the
> synchronization list.
>
> To resolve this issue, either recreate the missing sequence on the
> publisher using CREATE SEQUENCE, drop the sequences on the subscriber
> if they are no longer needed using DROP SEQUENCE, or run ALTER
> SUBSCRIPTION ... REFRESH PUBLICATION to remove these sequences from
> synchronization on the subscriber.

Modified

The attached v20250716 version patch has the changes for the same.

Regards,
Vignesh