Tomcat 8's Performance Penalty

A really simple project: https://github.com/lwr/tomcat8-custom-loader

What’s the problem

You should read this thread (Warning: TL;DR)

https://issues.apache.org/bugzilla/show_bug.cgi?id=57251

Conclusions:

• Tomcat 8 has a sensitive startup performance penalty if you use unpackWARs="false"
• Mark Thomas (from Tomcat) do not like this options

• They do not plan to solve this problem, and leave a guide as

  • use unique appBase values per Host
  • place the WARs outside all appBases
  • use context.xml files to add apps to a Host
  • leave unpackWARs as the default of true

• They even want to remove it in future

What it solves

Now use a custom loader from this project (currently 0.5) fix some problems:

• Startup performance Testing on a little test war from springframework about 7MB, the loading time

  • Using default loader: about 31 seconds
  • Using custom loader: about 8 seconds

• CustomClassLoader’s getURLs returns file:yy.jar URLs instead of jar:xx.war!/WEB-INF/yy.jar URLs

  That helps discovering classes in apps more easily

How to use

Build the project first, using

mvn package

or

mvn install

Then

1. drop the jar from target to your tomcat’s ${catalina.base}/lib
2. edit ${catalina.base}/conf/context.xml

3. add this line to context.xml

   <Loader loaderClass="com.github.lwr.tomcat8.CustomWebappClassLoader"/>
   

   (after edited)

   <!-- The contents of this file will be loaded for each web application -->
   <Context>
       ... ...
   
       <!-- Bellow is the added new line -->
       <Loader loaderClass="com.github.lwr.tomcat8.CustomWebappClassLoader"/>
   </Context>
   

4. start / restart your tomcat to check the load time

About hacking and maintainability

It is not a perfect project, and it uses some hacks such as

• StandardRoot.classResources is immutable, so reflection is used for modify it’s content
• JarWarResourceSet.archivePath is not accessible, so reflection is used because there no other choice

And Tomcat do not guarantee any undocumented API changes so that they could be change eventually, so this workaround maybe broken in the future. I will try to fix it if this occurs.

I hope they will change their mind to bring back this NON-FEATURE (expand all jars while unpackWARS=false)