Horton

Re: Logical Replication of sequences

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: vignesh C <vignesh21@gmail.com>
Cc: Peter Smith <smithpb2250@gmail.com>, Shlok Kyal <shlok.kyal.oss@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Euler Taveira <euler@eulerto.com>, Michael Paquier <michael@paquier.xyz>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Hou, Zhijie/侯 志杰 <houzj.fnst@fujitsu.com>, "Jonathan S. Katz" <jkatz@postgresql.org>, shveta malik <shveta.malik@gmail.com>
Date: 2024-09-26T05:37:25Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Doc: Add documentation for sequence synchronization.

  2. Remove unused assignment in CREATE PUBLICATION grammar.

  3. Add seq_sync_error_count to subscription statistics.

  4. Fix few issues in commit 5509055d69.

  5. Add sequence synchronization for logical replication.

  6. Add worker type argument to logical replication worker functions.

  7. Introduce "REFRESH SEQUENCES" for subscriptions.

  8. Refactor logical worker synchronization code into a separate file.

  9. Standardize use of REFRESH PUBLICATION in code and messages.

  10. Add "ALL SEQUENCES" support to publications.

  11. Expose sequence page LSN via pg_get_sequence_data.

  12. Resume conflict-relevant data retention automatically.

  13. Post-commit review fixes for 228c370868.

  14. Generate GUC tables from .dat file

On Fri, Sep 20, 2024 at 9:36 AM vignesh C <vignesh21@gmail.com> wrote:
>
> On Wed, 21 Aug 2024 at 11:54, vignesh C <vignesh21@gmail.com> wrote:
> >
> > On Wed, 21 Aug 2024 at 08:33, Peter Smith <smithpb2250@gmail.com> wrote:
> > >
> > > Hi Vignesh, Here are my only review comments for the latest patch set.
> >
> > Thanks, these issues have been addressed in the updated version.
> > Additionally, I have fixed the pgindent problems that were reported
> > and included another advantage of this design in the file header of
> > the sequencesync file.
>
> The patch was not applied on top of head, here is a rebased version of
> the patches.
> I have also removed an invalidation which was  not required for
> sequences and a typo.
>

Thank You for the patches. I would like to understand srsublsn and
page_lsn more. Please see the scenario below:

I have a sequence:
CREATE SEQUENCE myseq0 INCREMENT 5 START 100;

After refresh on sub:
postgres=# ALTER SUBSCRIPTION sub1 REFRESH PUBLICATION SEQUENCES;
ALTER SUBSCRIPTION

postgres=# select * from pg_subscription_rel;
 srsubid | srrelid | srsubstate | srsublsn
---------+---------+------------+-----------
   16385 |   16384 | r          | 0/152F380 -->pub's page_lsn


postgres=# select * from pg_sequence_state('myseq0');
 page_lsn  | last_value | log_cnt | is_called
-----------+------------+---------+-----------
 0/152D830 |        105 |      31 | t   -->(I am assuming 0/152D830 is
local page_lsn corresponding to value-=105)

Now I assume that *only* after doing next_wal for 31 times,  page_lsn
shall change. But I observe strange behaviour

After running nextval on sub for 7 times:
postgres=# select * from pg_sequence_state('myseq0');
 page_lsn  | last_value | log_cnt | is_called
-----------+------------+---------+-----------
 0/152D830 |        140 |      24 | t   -->correct

After running nextval on sub for 15 more times:
postgres=# select * from pg_sequence_state('myseq0');
 page_lsn  | last_value | log_cnt | is_called
-----------+------------+---------+-----------
 0/152D830 |        215 |       9 | t -->correct
(1 row)

Now after running it 6 more times:
postgres=# select * from pg_sequence_state('myseq0');
 page_lsn  | last_value | log_cnt | is_called
-----------+------------+---------+-----------
 0/152D990 |        245 |      28 | t --> how??

last_value increased in the expected way (6*5), but page_lsn changed
and log_cnt changed before we could complete the remaining runs as
well. Not sure why??

Now if I do refresh again:

postgres=# ALTER SUBSCRIPTION sub1 REFRESH PUBLICATION SEQUENCES;
ALTER SUBSCRIPTION

postgres=# select * from pg_subscription_rel;
 srsubid | srrelid | srsubstate | srsublsn
---------+---------+------------+-----------
   16385 |   16384 | r          | 0/152F380-->pub's page_lsn, same as old one.

postgres=# select * from pg_sequence_state('myseq0');
 page_lsn  | last_value | log_cnt | is_called
-----------+------------+---------+-----------
 0/152DDB8 |        105 |      31 | t
(1 row)

Now, what is this page_lsn = 0/152DDB8? Should it be the one
corresponding to last_value=105 and thus shouldn't it match the
previous value of  0/152D830?

thanks
Shveta