Re: Logical Replication of sequences

On Sat, May 3, 2025 at 7:27 PM vignesh C <vignesh21@gmail.com> wrote:
>
> >
> > Thanks for the comments, the updated patch has the changes for the same.
>

Thanks for the patches. Please find few comments:


1)
patch004 commit msg:
- Drop published sequences are removed from pg_subscription_rel.

Drop -->Dropped


2)
copy_sequences:

LOG:  Executing query :SELECT s.schname, s.seqname, ps.*, seq.seqtypid,
       seq.seqstart, seq.seqincrement, seq.seqmin,
       seq.seqmax, seq.seqcycle
FROM ( VALUES ('public', 'myseq1'), ('public', 'myseq3') ) AS s
(schname, seqname)
JOIN LATERAL pg_sequence_state(s.schname, s.seqname) ps ON true
....

Do we really need to log this query? If so, shall it be DEBUG1/DEBUG2?


3)
In log, we get:

------------------
LOG:  logical replication synchronized 9 of 9 sequences for subscription "sub1"
WARNING:  parameters differ for the remote and local sequences
("public.myseq1", "public.myseq3") for subscription "sub1"

LOG:  logical replication synchronized 2 of 2 sequences for subscription "sub1"
WARNING:  parameters differ for the remote and local sequences
("public.myseq1", "public.myseq3") for subscription "sub1"
------------------

This is confusing. I have 9 sequences, out of which 2 are mismatched.
So on REFRESH I get the first message as 'synchronized 9 of 9' and
later when it attempts to resynchronize pending ones automatically, it
keeps on displaying  'synchronized 2 of 2'.

Can we mention something like below:
-----------------
Unsynchronized sequences: 9, attempted in this batch: 9, succedded: 7,
mismatched/failed:2

So that if it is more than 100, say 120, it will say:
Unsynchronized sequences: 120, attempted in this batch: 100,
succedded: 98, mismatched/failed:2
And in next batch:
Unsynchronized sequences: 120, attempted in this batch: 20, succedded:
20, mismatched:0

And while attempting to synchronize failed ones, it will say:
Unsynchronized sequences: 2, attempted in this batch: 2, succedded: 0,
mismatched:2
-----------------

Please feel free to change the words. The intent is to get a clear
picture on what is happening.


4)
Why in patch001, we have 'pg_sequence_state' with one argument while
in 4ht patch it is changed to 2 args? Is it intentional to have it the
current way in patch001?


5)
Section1:
  <para>
   A new <firstterm>sequence synchronization worker</firstterm> will be started
   after executing any of the above subscriber commands, and will exit once the
   sequences are synchronized.
  </para>

Section2:
  <sect2 id="sequence-definition-mismatches">
   <title>Sequence Definition Mismatches</title>
   <warning>
    <para>
     During sequence synchronization, the sequence definitions of the publisher
     and the subscriber are compared. A WARNING is logged if any differences
     are detected.
    </para>
   </warning>


None of the section mentions that the synchronization worker will keep
on attempting to synchronize the failed/mismtached sequences until the
differences are resolved (provided disable_on_error is not enabled).
I think we can mention such a thing briefly in
'sequence-definition-mismatches' section.


thanks
Shveta