Replica Lag in PostgreSQL

Replica Lag in PostgreSQL

It can be calculated in two ways - 

1. Time 

2. Bytes

Time

SELECT

CASE

WHEN pg_last_wal_receive_lsn() = pg_last_wal_replay_lsn() THEN 0

ELSE EXTRACT (EPOCH FROM now() - pg_last_xact_replay_timestamp())::INTEGER

END

AS replication_lag;

replication_lag

-----------------

              28

(1 row)

Bytes

postgres=# SELECT client_addr, pg_wal_lsn_diff(pg_stat_replication.sent_lsn, pg_stat_replication.replay_lsn) AS byte_lag FROM pg_stat_replication;

client_addr | byte_lag

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

127.0.0.1   |        0

(1 row)

postgres=#