We have a streaming replication setup, where the replication slave runs pg_dump every hour. Our lag monitor shows an expected sawtooth shape, where pg_dump runs coincide with a climbing lag, which ends abruptly when pg_dump is finished. This is, to the best of my knowledge, expected behaviour. The lag pattern occasionally disappears though, and when looking at system processes we see that the database is recovering WAL data, and pg_dump is also running. How is this even possible?
FWIW, Master is running PostgreSQL 9.3.5-2.pgdg12.4+1 and the slave 9.3.6-1.pgdg12.4+1, and both running on Ubuntu 12.04 LTS.
Cheers,
Matt