diff --git a/Gemfile b/Gemfile
index 3b1b2cd2..0b94f0ed 100644
--- a/Gemfile
+++ b/Gemfile
@@ -19,7 +19,7 @@ gem 'kramdown'
 gem 'newrelic_rpm'
 gem 'pg', platform: :ruby
 gem 'pry'
-gem 'puma'
+gem 'puma', '~> 2.15.3'
 gem 'pundit'
 gem 'rails', '~> 4.1.2'
 gem 'rails-i18n', '~> 4.0.0'
diff --git a/Gemfile.lock b/Gemfile.lock
index d27789ea..245de4e7 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -185,13 +185,11 @@ GEM
       method_source (~> 0.8.1)
       slop (~> 3.4)
       spoon (~> 0.0)
-    puma (2.11.1)
-      rack (>= 1.1, < 2.0)
-    puma (2.11.1-java)
-      rack (>= 1.1, < 2.0)
+    puma (2.15.3)
+    puma (2.15.3-java)
     pundit (0.3.0)
       activesupport (>= 3.0.0)
-    rack (1.5.2)
+    rack (1.5.5)
     rack-test (0.6.3)
       rack (>= 1.0)
     rails (4.1.10)
@@ -368,7 +366,7 @@ DEPENDENCIES
   nyan-cat-formatter
   pg
   pry
-  puma
+  puma (~> 2.15.3)
   pundit
   rails (~> 4.1.2)
   rails-i18n (~> 4.0.0)
diff --git a/config/application.rb b/config/application.rb
index 744438a9..4b2a543a 100644
--- a/config/application.rb
+++ b/config/application.rb
@@ -33,6 +33,8 @@ module CodeOcean
     case (RUBY_ENGINE)
       when 'ruby'
         # ...
+        #this is enabled in prod for testing
+        config.middleware.use ActiveRecord::ConnectionAdapters::ConnectionManagement
       when 'jruby'
         # plattform specific
         java.lang.Class.for_name('javax.crypto.JceSecurity').get_declared_field('isRestricted').tap{|f| f.accessible = true; f.set nil, false}
diff --git a/config/docker.yml.erb b/config/docker.yml.erb
index 9f916acc..5ac309e8 100644
--- a/config/docker.yml.erb
+++ b/config/docker.yml.erb
@@ -18,8 +18,8 @@ production:
     active: true
     refill:
       async: false
-      batch_size: 32
-      interval: 30
+      batch_size: 8
+      interval: 15
       timeout: 60
   workspace_root: <%= Rails.root.join('tmp', 'files', Rails.env) %>
   ws_host: ws://localhost:4243
diff --git a/lib/docker_container_pool.rb b/lib/docker_container_pool.rb
index 5ff25da6..2ce75e10 100644
--- a/lib/docker_container_pool.rb
+++ b/lib/docker_container_pool.rb
@@ -73,7 +73,7 @@ class DockerContainerPool
   end
 
   def self.refill
-    ExecutionEnvironment.where('pool_size > 0').each do |execution_environment|
+    ExecutionEnvironment.where('pool_size > 0').order(pool_size: :desc).each do |execution_environment|
       if config[:refill][:async]
         Concurrent::Future.execute { refill_for_execution_environment(execution_environment) }
       else
@@ -99,7 +99,7 @@ class DockerContainerPool
   end
 
   def self.start_refill_task
-    @refill_task = Concurrent::TimerTask.new(execution_interval: config[:refill][:interval], run_now: false, timeout_interval: config[:refill][:timeout]) { refill }
+    @refill_task = Concurrent::TimerTask.new(execution_interval: config[:refill][:interval], run_now: true, timeout_interval: config[:refill][:timeout]) { refill }
     @refill_task.execute
   end
 end