Try resetting DB connection in case of a PG::UnableToSend exception

Gemfile.lock

 PATH
   remote: .
   specs:
-    gitlab-monitor (2.1.0)
+    gitlab-monitor (2.2.0)
       connection_pool (~> 2.2.1)
       pg (~> 0.18.4)
       quantile (~> 0.2.0)

lib/gitlab_monitor/database/base.rb

@@ -27,6 +27,17 @@ module GitLab
         def connection_pool
           self.class.connection_pool[@connection_string]
         end
+
+        def with_connection_pool(&block)
+          connection_pool.with do |conn|
+            begin
+              yield conn
+            rescue PG::UnableToSend => e
+              conn.reset
+              raise e
+            end
+          end
+        end
       end
     end
   end

lib/gitlab_monitor/database/ci_builds.rb

@@ -178,7 +178,7 @@ module GitLab
         end
 
         def stale_builds
-          connection_pool.with do |conn|
+          with_connection_pool do |conn|
             conn.exec(STALE_BUILDS_QUERY)[0]["count"].to_i
           end
         rescue PG::UndefinedTable, PG::UndefinedColumn
@@ -221,7 +221,7 @@ module GitLab
         end
 
         def exec_query_with_custom_random_page_cost(query)
-          connection_pool.with do |conn|
+          with_connection_pool do |conn|
             conn.transaction do |trans|
               trans.exec(SET_RANDOM_PAGE_COST)
               trans.exec(query)
@@ -232,7 +232,7 @@ module GitLab
         def mirror_column?
           @mirror_column ||=
             begin
-              connection_pool.with do |conn|
+              with_connection_pool do |conn|
                 conn.exec(MIRROR_COLUMN_QUERY)[0]["exists"] == "t"
               end
             rescue PG::UndefinedColumn

lib/gitlab_monitor/database/row_count.rb

@@ -30,7 +30,7 @@ module GitLab
         private
 
         def execute(query)
-          connection_pool.with do |conn|
+          with_connection_pool do |conn|
             conn.exec(construct_query(query))[0]["count"]
           end
         rescue PG::UndefinedTable, PG::UndefinedColumn

lib/gitlab_monitor/database/tuple_stats.rb

@@ -15,7 +15,7 @@ module GitLab
         SQL
 
         def run
-          connection_pool.with do |conn|
+          with_connection_pool do |conn|
             conn.exec(QUERY).each.with_object({}) do |row, stats|
               stats[row.delete("relname")] = row
             end

lib/gitlab_monitor/version.rb

 module GitLab
   module Monitor
-    VERSION = "2.1.0".freeze
+    VERSION = "2.2.0".freeze
   end
 end