IBM Support

Slow WebSphere Application Server performance after increase of Java stack (Xss)

Troubleshooting


Problem

WSAS takes very long time to parse a large XML file after increase of Java stack value (Xss).

Symptom

A specific application parsing a very large XML file encountered a java.lang.StackOverflowError; the nature of this application necessitated to increase the Java stack value (Xss) to overcome the error.

(e.g. to increase the Java stack to 10M one would set JVM generic argument -Xss10M), as described in this technote: "Diagnosing a java.lang.StackOverflowError" referenced below)

Cause

A consequence of increasing the Java stack, is that on program execution the JIT will spend significant amount of time in stack walking.

In the current implementation, the initial value of the Java stack (Xss) is 2k and the increment (Xssi) is 16k, therefore in the above example, there will be many stack growth operations before it reaches the targeted 10M Java stack value (Xss) which in turn involves many expensive JIT stack walks.
(For reference to the "Default settings for the JVM", see link provided further down.

Resolving The Problem

The solution to the initial slow performance caused by the many JIT stack walks is to set the initial stack value (Xiss) to be equal to the Xss value.
(An alternative would be to use a bigger increment size than 16k, using parameter Xssi).

[{"Product":{"code":"SSEQTP","label":"WebSphere Application Server"},"Business Unit":{"code":"BU053","label":"Cloud & Data Platform"},"Component":"Performance and High CPU Utilization","Platform":[{"code":"PF002","label":"AIX"},{"code":"PF016","label":"Linux"},{"code":"PF033","label":"Windows"}],"Version":"8.5.5;8.5;8.0;7.0","Edition":"","Line of Business":{"code":"LOB45","label":"Automation"}}]

Document Information

Modified date:
15 June 2018

UID

swg21659956