Create multiple logical replication slots

[MilenBlagojevic]

Hello,

I have simple setup with primary and one streaming replica. pg_failover_slots extension on both of them is configured and working.

Then, I create 2 logical replication slots:

publisher=# SELECT * FROM pg_create_logical_replication_slot('logical_replication_slot_1', 'test_decoding');
         slot_name          |     lsn
----------------------------+-------------
 logical_replication_slot_1 | 7C/36191128
(1 row)


publisher=# SELECT * FROM pg_create_logical_replication_slot('logical_replication_slot_2', 'test_decoding');
         slot_name          |     lsn
----------------------------+-------------
 logical_replication_slot_2 | 7C/36191160
(1 row)

publisher=# select * from 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
----------------------------+---------------+-----------+---------+----------+-----------+--------+------------+-----------+--------------+-------------+---------------------+------------+---------------
 logical_replication_slot_1 | test_decoding | logical   | 1037644 | publisher| f         | f      |            |           |    119372965 | 7C/361910F0 | 7C/36191128         | reserved   |
 logical_replication_slot_2 | test_decoding | logical   | 1037644 | publisher| f         | f      |            |           |    119372965 | 7C/36191128 | 7C/36191160         | reserved   |
 physical_repl              |               | physical  |         |          | f         | t      |      16192 | 119372999 |    119372999 | 7C/3715F4A8 |                     | reserved   |
(3 rows)

Streaming replica shows one of them:

publisher=# select * from 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
----------------------------+---------------+-----------+---------+----------+-----------+--------+------------+------+--------------+-------------+---------------------+------------+---------------
 logical_replication_slot_1 | test_decoding | logical   | 1037644 | publisher| f         | t      |       3457 |      |    119372999 | 7C/3407FF88 |                     | reserved   |
(1 row)

And the failover_worker on it logs these warnings:

still waiting for remote slot logical_replication_slot_1 lsn (7C/361910F0) and catalog xmin (119372965) to pass local slot lsn (7C/3407FF88) and catalog xmin (119372999)

So, even if there are some changes for logical_replication_slot_2, its position is not being synced to streaming replica, because logical_replication_slot_1 is not consumed.

Should pg_failover_slots work like this?

I know the workaround would be to consume logical_replication_slot_1 one first and then create logical_replication_slot_2.

Regards,
Milen