RPO vs RTO Disaster Recovery:

In Simple Words:

• RPO (Recovery Point Objective): Maximum acceptable data loss duration (e.g. at most 5 mins of data).
• RTO (Recovery Time Objective): Maximum acceptable downtime duration to restore service (e.g. restore within 15 mins).

-- Verifying replication lag for RPO in PostgreSQL:
SELECT client_addr, application_name,
  pg_wal_lsn_diff(pg_current_wal_lsn(), replay_lsn) AS replication_lag_bytes
FROM pg_stat_replication;