Re: Logical Replication of sequences

On Wed, 5 Nov 2025 at 15:11, shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> Please find a few comments on 003 patch (seqsync_error_count)
>
> 1)
> + /*
> + * Report the worker failed during either sequence synchronization or
> + * table synchronization or apply.
> + */
>
> Shall we tweak it slightly to:
> Report the worker failed during sequence synchronization, table
> synchronization, or apply.

Modified

> 2)
>
> + SELECT count(1) = 1 FROM pg_stat_subscription_stats
> + WHERE subname = '$sub_name' and seq_sync_error_count > 0 and
> sync_error_count > 0
> ])
> or die
> qq(Timed out while waiting for tablesync errors for subscription
> '$sub_name');
>
> Since we are checking both table-sync and seq-sync errors here, we
> shall update the failure-message.

Modified

> 3)
> + # Change the sequence start value on the subscriber so that it
> doesn't error out.
> + $node_subscriber->safe_psql($db,
> + qq(ALTER SEQUENCE $sequence_name INCREMENT 1));
>
> Please mention in comment 'Change the sequence start value to default....'.
> Otherwise it is not clear why changing to 1 is helping here as the
> previous creation of seq on pub did not mention any 'INCREMENT' value
> at all.

Modified

> 4)
>
> - # Wait for initial tablesync to finish.
> + # Wait for initial sync to finish.
> $node_subscriber->poll_query_until(
> $db,
> qq[
> - SELECT count(1) = 1 FROM pg_subscription_rel
> - WHERE srrelid = '$table_name'::regclass AND srsubstate in ('r', 's')
> + SELECT count(1) = 2 FROM pg_subscription_rel
> + WHERE srrelid IN ('$table_name'::regclass,
> '$sequence_name'::regclass) AND srsubstate in ('r', 's')
> ])
> or die
> qq(Timed out while waiting for subscriber to synchronize data for
> table '$table_name'.);
>
>
> a) Will it be better to separate the 2 queries as the table-sync can
> be 'r' and 's', while seq-sync has to be 'r'.
>
> b) If we plan to keep the same as above, the failure-message needs to
> be changed as it mentions only table.

I have separated the query to check individually for table sync and
sequence sync.

The attached v20251105 version patch has the changes for the same.

Regards,
Vignesh