Thread
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Re: Logical Replication of sequences
Nisha Moond <nisha.moond412@gmail.com> — 2025-06-30T09:50:00Z
On Fri, Jun 27, 2025 at 8:50 AM shveta malik <shveta.malik@gmail.com> wrote: > > On Wed, Jun 25, 2025 at 7:42 PM Shlok Kyal <shlok.kyal.oss@gmail.com> wrote: > > Hi Vignesh, > > > > I tested with all patches applied. I have a comment: > > > > Let consider following case: > > On publisher create a publication pub1 on all sequence. publication > > has sequence s1. The curr value of s1 is 2 > > and On subscriber we have subscription on pub1 and sequence s1 has > > value 5. Now we run: > > "ALTER SUBSCRIPTION sub1 REFRESH PUBLICATION SEQUENCES" > > > > Now on subscriber currval still show '5': > > postgres=# select currval('s1'); > > currval > > --------- > > 5 > > (1 row) > > > > But when we do nextval on s1 on subscriber we get '3'. Which is > > correct assuming sequence is synced: > > postgres=# select nextval('s1'); > > nextval > > --------- > > 3 > > (1 row) > > postgres=# select currval('s1'); > > currval > > --------- > > 3 > > (1 row) > > > > Is this behaviour expected? I feel the initial " select > > currval('s1');" should have displayed '2'. Thoughts? > > As per docs at [1], currval returns the value most recently obtained > by nextval for this sequence in the current session. So behaviour is > in alignment with docs. I tested this across multiple sessions, > regardless of whether sequence synchronization occurs or not. The > behavior remains consistent across sessions. As an example, if in > session2 the sequence has advanced to a value of 10 by calling > nextval, the currval in session1 still shows the previous value of 3, > which was obtained by nextval in session1. So, it seems expected to > me. But let's wait for Vignesh's comments on this. > > [1]: https://www.postgresql.org/docs/current/functions-sequence.html > I also agree. It is expected behavior, as currval returns the last nextval generated in the same session. I've also observed this across multiple sessions. -- Thanks, Nisha