Merge pull request #22 from greigwise/master

Fix connections metric to work with postgres 9.6+

Author: eheydrick

CHANGELOG.md

@@ -4,6 +4,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 This CHANGELOG follows the format listed at [Keep A Changelog](http://keepachangelog.com/)
 
 ## [Unreleased]
+### Fixed
+- metric-postgres-connections: Handle postgres version 9.6 and above.
+
 ### Changed
 - Updated all the scripts to add an optional timeout setting.
 

bin/metric-postgres-connections.rb

@@ -81,8 +81,17 @@ def run
                          password: config[:password],
                          connect_timeout: config[:timeout])
     request = [
-      'select count(*), waiting from pg_stat_activity',
-      "where datname = '#{config[:database]}' group by waiting"
+      "select case when count(*) = 1 then 'waiting' else",
+      "'case when wait_event_type is null then false else true end' end as wait_col",
+      'from information_schema.columns',
+      "where table_name = 'pg_stat_activity' and table_schema = 'pg_catalog'",
+      "and column_name = 'waiting'"
+    ]
+    wait_col = con.exec(request.join(' ')).first['wait_col']
+
+    request = [
+      "select count(*), #{wait_col} as waiting from pg_stat_activity",
+      "where datname = '#{config[:database]}' group by #{wait_col}"
     ]
 
     metrics = {