[pgpool-general: 7410] pcp_node_info does not show replication info in MASTER-SLAVE mode

[Láznička Vladimír]

Hello,

We've recently switched our pgPool/PostgreSQL cluster from the native replication to MASTER-SLAVE replication (streaming replication via replication slots). Everything seems to be working just fine (like failover, online recovery or load balancing), but if I query the node status with pcp_node_info command, the information about replication state does not get displayed:

[pgpool at AISGPGP01 ~]$ pcp_node_info -h /home/pgpool/pcp_socket_dir --no-password -v 0
Hostname               : aisgdbd01.cca.cz
Port                   : 5432
Status                 : 2
Weight                 : 0.500000
Status Name            : up
Role                   : primary
Replication Delay      : 0
Replication State      :
Replication Sync State :
Last Status Change     : 2021-02-01 16:07:01

The same can be observed, when I try to query the node status with SQL command:

aisgdvyv=# SHOW POOL_NODES;
node_id |     hostname     | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | replication_state | replication_sync_state | last_status_change
---------+------------------+------+--------+-----------+---------+------------+-------------------+-------------------+-------------------+------------------------+---------------------
0       | aisgdbd01.cca.cz | 5432 | up     | 0.500000  | primary | 1507331    | true              | 0                 |                   |                        | 2021-02-01 16:07:01
1       | aisgdbd02.cca.cz | 5432 | up     | 0.500000  | standby | 806751     | false             | 0                 |                   |                        | 2021-02-01 16:08:00

If I try to directly query the pg_stat_replication view on the PRIMARY, I get this result:

aisgdvyv=# SELECT * FROM pg_stat_replication;
-[ RECORD 1 ]----+------------------------------
pid              | 4429
usesysid         | 16393
usename          | replication
application_name | walreceiver
client_addr      | 172.20.15.67
client_hostname  |
client_port      | 32944
backend_start    | 2021-02-01 16:07:55.678388+01
backend_xmin     |
state            | streaming
sent_lsn         | E5/10170BD8
write_lsn        | E5/10170BD8
flush_lsn        | E5/10170BD8
replay_lsn       | E5/10170BD8
write_lag        | 00:00:00.000208
flush_lag        | 00:00:00.000907
replay_lag       | 00:00:00.000972
sync_priority    | 0
sync_state       | async

It seems like pgPool cannot access the information. I have created a user "pgpool_streamcheck" as a member of the group "pg_monitor" to be used for the replication delay check:

aisgdvyv=# \dg
                                              List of roles
      Role name      |                         Attributes                         |       Member of
---------------------+------------------------------------------------------------+-----------------------
...
pgpool_healthcheck  |                                                            | {}
pgpool_streamcheck  |                                                            | {pg_monitor}
postgres            | Superuser, Create role, Create DB, Replication, Bypass RLS | {}
replication         | Replication                                                | {}
...

>From the logs of pgPool it seems to be able to query the delay since I can occasionally see it exceeds the set threshold:

Feb  2 22:39:08 AISGPGP01 pgpool[28300]: [2205-1] 2021-02-02 22:39:08 ::: APP - [No Connection] :A: DB - [No Connection] :D: USER - [No Connection] :U: |LOG:  Replication of node:1 is behind 8224 bytes from the primary server (node:0)
Feb  2 22:39:08 AISGPGP01 pgpool[28300]: [2205-2] 2021-02-02 22:39:08 ::: APP - [No Connection] :A: DB - [No Connection] :D: USER - [No Connection] :U: |CONTEXT:  while checking replication time lag

I am sending you the pgpool.conf file as an attachment. Could you please look it over and tell me, if I have set something wrong? We are using the pgPool version 4.1.5 and the PostgreSQL version 11.10.

Thank you for your time.

With best regards,
Vladimír Láznička
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