RE: Logical replication from standby

Hi admins,

It seams that my problem is not common. Actualy it is.

Because there is no postgresql traffic in my testnig envoronment, I have to run »SELECT * FROM pg_log_standby_snapshot();« on primary for each (!!!!) table in database I replicated. ☹

Best regards!

Domen Šetar
Computer Systems Support
IZUM – Institute of Information Science | Prešernova ulica 17 | 2000 Maribor | Slovenia
T: +386 2 25 20 339 | M: +386 41 676 342 | <http://www.izum.si/> www.izum.si | <mailto:domen(dot)setar(at)izum(dot)si> domen(dot)setar(at)izum(dot)si

From: Domen Šetar
Sent: Friday, March 1, 2024 10:28 AM
To: pgsql-admin(at)lists(dot)postgresql(dot)org
Subject: Logical replication from standby

Hi admins,

I'm just in testing phase of logical replication from standby server on postgresql 16.

I have some expirience in logical replication on postgresql 14. Common behaviour was that after starting logical replication of all tables in database I have some additional pg_*_sync_* replication slots. After all tables were synchronized all *sync* replications slots disapeared and only replication slot that I created stays in place.

On logical replication from standby I see folowing state on my standby server:

postgres=# SELECT * FROM pg_catalog.pg_replication_slots;

slot_name | plugin | slot_type | datoid | database | temporary | active | active_pid | xmin | catalog_xmin | restart_lsn | confirmed_flush_lsn | wal_status | safe_wal_

size | two_phase | conflicting

-------------------------------------------+----------+-----------+--------+----------+-----------+--------+------------+------+--------------+--------------+---------------------+------------+----------

-----+-----------+-------------

pg_204804_sync_202370_7340192741191578195 | pgoutput | logical | 168324 | c3_test | f | t | 2105026 | | 2006589 | C6E/50000B18 | | reserved |

| f | f

pg_204804_sync_201130_7340192741191578195 | pgoutput | logical | 168324 | c3_test | f | t | 2105025 | | 2006589 | C6E/50000B18 | | reserved |

| f | f

c3_test_subscription | pgoutput | logical | 168324 | c3_test | f | t | 2103843 | | 2006589 | C6E/50000AE0 | C6E/50000B18 | reserved |

| f | f

(3 rows)

I'm replicating small database of 25MB with less thant 140 tables.

As I can see database is sucessfully replicated but both *sync* replication slots stay in place.

Is this new behaviour for logical replication from standby, or did I miss something?

Best regards!

Domen Šetar
Computer Systems Support
IZUM – Institute of Information Science | Prešernova ulica 17 | 2000 Maribor | Slovenia
T: +386 2 25 20 339 | M: +386 41 676 342 | <http://www.izum.si/> www.izum.si | <mailto:domen(dot)setar(at)izum(dot)si> domen(dot)setar(at)izum(dot)si