Fixes replication check compatibility in PG 10

Author: phumpal

CHANGELOG.md

@@ -4,6 +4,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 This CHANGELOG follows the format listed [here](https://github.com/sensu-plugins/community/blob/master/HOW_WE_CHANGELOG.md).
 
 ## [Unreleased]
+### Fixed
+- check-postgres-replication.rb: maintains backwards compatibility with <= 9.6 and adds compatibility for >= 10
 
 ## [1.4.2] - 2017-09-27
 ### Fixed

bin/check-postgres-replication.rb

@@ -117,7 +117,13 @@ def run
                              sslmode: ssl_mode,
                              connect_timeout: config[:timeout])
 
-    master = conn_master.exec('SELECT pg_current_xlog_location()').getvalue(0, 0)
+    begin
+      # PostgreSQL 10
+      master = conn_master.exec('SELECT pg_current_wal_lsn()').getvalue(0, 0)
+    rescue
+      # PostgreSQL <= 9.6
+      master = conn_master.exec('SELECT pg_current_xlog_location()').getvalue(0, 0)
+    end
     m_segbytes = conn_master.exec('SHOW wal_segment_size').getvalue(0, 0).sub(/\D+/, '').to_i << 20
     conn_master.close
 
@@ -130,7 +136,13 @@ def run
                             sslmode: ssl_mode,
                             connect_timeout: config[:timeout])
 
-    slave = conn_slave.exec('SELECT pg_last_xlog_receive_location()').getvalue(0, 0)
+    begin
+      # PostgreSQL 10
+      slave = conn_slave.exec('SELECT pg_last_wal_replay_lsn()').getvalue(0, 0)
+    rescue
+      # PostgreSQL <= 9.6
+      slave = conn_slave.exec('SELECT pg_last_xlog_receive_location()').getvalue(0, 0)
+    end
     conn_slave.close
 
     # Computing lag