[PostgreSQL] How to verify if replication catch up with master change

[Run on master] Check master location with

SELECT pg_current_xlog_location();

 [Run on replica] Check replica replayed location with

SELECT pg_last_xlog_replay_location();

[Run on master] Check replica status from master

SELECT client_addr, state, sent_location, write_location, flush_location, replay_location FROM pg_stat_replication;

*write, flush, replay are status of replica

[Run on replica] Check time from the latest reply

SELECT now() - pg_last_xact_replay_timestamp() AS replication_delay;

Credit:

• Bullet 12th of https://wiki.postgresql.org/wiki/Streaming_Replication
• https://www.niwi.nz/2013/02/16/replication-status-in-postgresql/