Re: Monitoring of a hot standby with a largely idle master

On Thu, Jul 13, 2017 at 5:26 AM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
>
> I think that none of the recovery information functions
> (https://www.postgresql.org/docs/9.6/static/functions-admin.html#FUNCTIONS-RECOVERY-INFO-TABLE)
> can distinguish a hot standby which is connected to an idle master, versus
> one which is disconnected. For example, because the master has crashed, or
> someone has changed the firewall rules.
>
> Is there a way to monitor from SQL the last time the standby was able to
> contact the master and initiate streaming with it? Other than trying to
> write a function that parses it out of pg_log?

Not directly I am afraid. One way I can think about is to poll
periodically the state of pg_stat_replication on the primary or
pg_stat_wal_receiver on the standby and save it in a custom table. The
past information is not persistent as any replication-related data in
catalogs is based on the shared memory state of the WAL senders and
the WAL receiver, and those are wiped out at reconnection.
--
Michael