Run two threads to improve migration running time

db/post_migrate/20170206040400_remove_inactive_default_email_services.rb

@@ -4,24 +4,38 @@ class RemoveInactiveDefaultEmailServices < ActiveRecord::Migration
   DOWNTIME = false
 
   def up
-    execute <<-SQL.strip_heredoc
+    builds_service = spawn <<-SQL.strip_heredoc
       DELETE FROM services
         WHERE type = 'BuildsEmailService'
           AND active = #{false_value}
           AND properties = '{"notify_only_broken_builds":true}';
+    SQL
 
+    pipelines_service = spawn <<-SQL.strip_heredoc
       DELETE FROM services
         WHERE type = 'PipelinesEmailService'
           AND active = #{false_value}
           AND properties = '{"notify_only_broken_pipelines":true}';
     SQL
+
+    [builds_service, pipelines_service].each(&:join)
   end
 
-  def false_value
-    quote(false)
+  private
+
+  def spawn(query)
+    Thread.new do
+      ActiveRecord::Base.connection_pool.with_connection do
+        ActiveRecord::Base.connection.execute(query)
+      end
+    end
   end
 
   def quote(value)
     ActiveRecord::Base.connection.quote(value)
   end
+
+  def false_value
+    quote(false)
+  end
 end