Assume a master -> slave streaming replication configuration, Postgresql 9.2. Assume that the master has been chugging away, but the slave PG service has been offline for a while and the wal archive has updated enough that the slave cannot catch up.
When I start the slave PG instance, pg launches and "runs" but doesn't update. It also doesn't seem to throw any errors. The only outward sign that I can see that anything is wrong is that pg_last_xlog_replay_location() doesn't update. I can look in /var/lib/pgsql/9.2/data/pg_log/postgresql-Thu.csv and see errors there EG:
2014-07-17 22:38:23.851 UTC,,,21310,,53c8505f.533e,2,,2014-07-17 22:38:23 UTC,,0,FATAL,XX000,"could not receive data from WAL stream: FATAL: requested WAL segment 000000070000000500000071 has already been removed
Is that the only way to detect this condition? I guess I'm looking for something like
select * from pg_is_replicating_ok(); 1
on the slave. At the moment, it appears that I can either parse the log file, or look for pg_last_xact_replay_timestamp() > acceptable threshold minutes in the past.