How can you calculate the master-slave replication latency. postgres 9.2.7?

Question

PostgreSQL

How can I calculate master-slave replication latency in postgres?
I get the value of the lag, but this value is quite abstract, I would like to get exactly the delay time.

Answer 1

select now() - pg_last_xact_replay_timestamp();
run on standby via psql, get the lag in seconds.

Answer 2

Mhm. There is one universal way for all bases.
In a separate table on the master every second-five-ten (depending on the desired error and load) write the current time. And on the replica, check how much this table lags behind real time.