Enable compression in Tomcat

When page loading is too slow in a Semarchy xDM application, bad performance could be related to :

• SQL query processing time  ( see Enable Logging in Semarchy xDM for reference on how to track and capture long-running queries )
• lack of horsepower and RAM on the application server ( check RAM and CPU usage on the host, verify connection pool sizing vs number of users, and tomcat memory settings )
• slow network

This article will focus on the latter. 

Big files ?

When a semarchy form is loaded for the first time in the current session, the browser downloads a json file that describes the page layout. For complicated BoViews with multiple tabs and transitions, this json file could weigh 6 Mo or more. This can significantly increase page loading time if you have a low bandwidth and / or when the application server is far 

Then what ?

The tomcat application server (as most application servers) can compress some of the resources used in a HTML page before transferring them over the network. There's a slight processing overhead to compress the files, but it's definitely worth it if network bandwidth is the main bottleneck.

There's a lot of structural redundancy in the average json file, making it a very good candidate for compression (you can expect more than 95 % reduction in size).

How can I monitor file tranfer duration ?

Google Chrome comes with a built-in troubleshooting tool (known as Developer Tools) that allows one to monitor the time taken to fetch files from the server to the client (the browser) :

• Press Ctrl + Shift + I to show / hide it.
• Make sure the Network tab is active / selected
• Use the clear button to clear the network log and make sure the "Disable Cache" property is ticked
• Refresh the page
• Locate the semRootEO file and check its size and transfer duration
• Select the file to see the current Content Type : it should be application/json

Step-by-step guide

1. Open the server.xml file with your favorite text editor (it's typically found in the tomcat_root/conf folder)
2. Locate the <Connector> element

3. Modify it  by adding three compression-related properties as follows

   	compression="on"
   	compressionMinSize="4096"
   	compressableMimeType="text/html,application/json"
   

4. Restart your tomcat server
5. Start developer tools in chrome, go to network tab, select the semRootEO file, and check the header to make sure the changes were applied : the content encoding should now be gzip 

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