Why is restart_lsn not set, even on checkpoint - postgresql

> A logical slot will emit each change just once in normal operation. > The current position of each slot is persisted only at checkpoint, so > in the case of a crash the slot may return to an earlier LSN, which > will then cause recent changes to be resent when the server restarts. > Logical decoding clients are responsible for avoiding ill effects from > handling the same message more than once. Clients may wish to record > the last LSN they saw when decoding and skip over any repeated data or > (when using the replication protocol) request that decoding start from > that LSN rather than letting the server determine the start point Quoted from [here](https://www.postgresql.org/docs/10/logicaldecoding-explanation.html) I'm implementing a logical (streaming) replication. Thus far things are looking good but I'm unable to understand why restart_lsn entry is not changed. i.e I do this.. SELECT * FROM pg_replication_slots; slot_name | plugin | slot_type | datoid | database | active | active_pid | xmin | catalog_xmin | restart_lsn -----------+----------+-----------+--------+----------+--------+------------+------+--------------+------------- pgx_test | wal2json | logical | 12641 | postgres | t | 16045 | | 8544916 | 2/B1BC5330 Insert 2/3 record SELECT * FROM pg_stat_replication; pid | usesysid | usename | application_name | client_addr | client_hostname | client_port | backend_start | backend_xmin | state | sent_location | write_location | flush_location | replay_location | sync_priority | sync_state -------+----------+-----------------+------------------+-------------+-----------------+-------------+----------------------------------+--------------+-----------+---------------+----------------+----------------+-----------------+---------------+------------ 16315 | 1601109 | pgx_replication | | 127.0.0.1 | | 50112 | 2019-03-11 17:33:18.150179+05:30 | | streaming | 2/B1BCA0F8 | | | | 0 | async The sent_location gets updated but not the restart_lsn, even though I ran a checkpoint command had set the checkoint_timeout=1m but still the replay_lsn does not change. SELECT * FROM pg_replication_slots; slot_name | plugin | slot_type | datoid | database | active | active_pid | xmin | catalog_xmin | restart_lsn -----------+----------+-----------+--------+----------+--------+------------+------+--------------+------------- pgx_test | wal2json | logical | 12641 | postgres | t | 16315 | | 8544916 | 2/B1BC5330 (1 row) Any reason why this happens?