Re: AW: AW: AW: Replication Testing- How to introduce a Lag

On Mon, 2026-03-23 at 05:55 +0000, Subramanian,Ramachandran wrote:
> Thank you so much for your guidance,  Today morning I noticed the columns being null . 
>
> > streaming | 0/491179E8 | 0/491179E8 | 0/491179E8 | 0/491179E8 |           |           |            |
>
> Does it make sense to use the below SQL as a primary health check ?
>
> [postgres(at)Source_server~]$ psql -p 5432 -c " select  pg_wal_lsn_diff(sent_lsn,replay_lsn) from pg_stat_replication"
>  pg_wal_lsn_diff
> -----------------
>                0
> (1 row)

No; you want to measure the lag between the primary's current WAL position and
what was already replayed on the standby:

SELECT pg_wal_lsn_diff(pg_current_wal_lsn(), replay_lsn)
FROM pg_stat_replication;

Yours,
Laurenz Albe