Re: Logical Replication of sequences

On Mon, Oct 27, 2025 at 10:04 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:

> On Mon, Oct 27, 2025 at 8:23 AM Zhijie Hou (Fujitsu) <
> houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
>> On Friday, October 24, 2025 11:22 PM vignesh C <vignesh21(at)gmail(dot)com>
>> wrote:
>> >
>> > On Thu, 23 Oct 2025 at 16:47, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
>> wrote:
>> > >
>> > > On Thu, Oct 23, 2025 at 11:45 AM vignesh C <vignesh21(at)gmail(dot)com>
>> wrote:
>> > > >
>> > > > The attached patch has the changes for the same.
>> > > >
>> > >
>> > > I have pushed 0001 and the following are comments on 0002.
>> >
>>
>
> One question, I am not sure if this has been discussed before, So while
> getting sequence information from remote we are also getting the page_lsn
> of the sequence and we are storing that in pg_subscription_rel. Is it just
> for the user to see and compare whether the sequence is synced to the
> latest lsn or is it used for anything else as well? In our patch sert, I
> don't see much usability information about this field.
>

Overall patch LGTM, and I really like the idea of getting rid of the hash
and converting it into a list, now we don't need to restart the scan unlike
hash due to transaction boundary. However I have one more suggestion.

/*
+ * Establish the connection to the publisher for sequence synchronization.
+ */
+ LogRepWorkerWalRcvConn =
+ walrcv_connect(MySubscription->conninfo, true, true,
+ must_use_password,
+ app_name.data, &err);
+ if (LogRepWorkerWalRcvConn == NULL)
+ ereport(ERROR,
+ errcode(ERRCODE_CONNECTION_FAILURE),
+ errmsg("sequencesync worker for subscription \"%s\" could not connect to
the publisher: %s",
+ MySubscription->name, err));
+
+ pfree(app_name.data);
+
+ /* If there are any sequences that need to be copied */
+ if (hash_get_num_entries(sequences_to_copy))
+ copy_sequences(LogRepWorkerWalRcvConn, subid);

I think we should call 'walrcv_connect' only if we need to copy_sequences
right?

--
Regards,
Dilip Kumar
Google