Following the recent post related to the extension that gives a representation of a WAL receiver doing WAL recovery via streaming, here is its equivalent in-core, for a new feature that will be available in Postgres 9.6:
commit: b1a9bad9e744857291c7d5516080527da8219854 author: Alvaro Herrera <email@example.com> date: Thu, 7 Jan 2016 16:21:19 -0300 pgstat: add WAL receiver status view & SRF This new view provides insight into the state of a running WAL receiver in a HOT standby node. The information returned includes the PID of the WAL receiver process, its status (stopped, starting, streaming, etc), start LSN and TLI, last received LSN and TLI, timestamp of last message send and receipt, latest end-of-WAL LSN and time, and the name of the slot (if any). Access to the detailed data is only granted to superusers; others only get the PID. Author: Michael Paquier Reviewer: Haribabu Kommi
So, what has been added here is a new system view called [pg_stat_wal_receiver] (https://www.postgresql.org/docs/devel/static/monitoring-stats.html#PG-STAT-WAL-RECEIVER-VIEW) that offers to the user a set of information equivalent to the extension presented in the previous post, except that this has the advantage to not rely on any external things, making it available immediately in-box, and to be precisely documented, for sure the best point. When connecting to a node performing streaming on the receiver-side, here is the information present:
=# \d pg_stat_wal_receiver View "pg_catalog.pg_stat_wal_receiver" Column | Type | Modifiers -----------------------+--------------------------+----------- pid | integer | status | text | receive_start_lsn | pg_lsn | receive_start_tli | integer | received_lsn | pg_lsn | received_tli | integer | last_msg_send_time | timestamp with time zone | last_msg_receipt_time | timestamp with time zone | latest_end_lsn | pg_lsn | latest_end_time | timestamp with time zone | slot_name | text | =# SELECT * FROM pg_stat_wal_receiver; -[ RECORD 1 ]---------+------------------------------ pid | 12939 status | streaming receive_start_lsn | 0/3000000 receive_start_tli | 1 received_lsn | 0/3000888 received_tli | 1 last_msg_send_time | 2016-01-09 21:19:03.812829+09 last_msg_receipt_time | 2016-01-09 21:19:03.812864+09 latest_end_lsn | 0/3000888 latest_end_time | 2016-01-09 21:19:03.812829+09 slot_name | null
If this system view is queried on a node that does not have a WAL receiver, no tuples are returned. In the case of a non-superuser, all fields are hidden except the process PID. This is going to be useful for monitoring purposes, and to ease lookups at the WAL receiver process, which was up to 9.5 something that users had to look at through for example ps with sometimes needs to directly parse its output.