What the performance impact of enabling WebSphere PMI

Question

I am currently looking at some JProfiler traces from our WebSphere-based application, and am noticing that a significant amount of CPU time is being spent in the class com.ibm.io.async.AsyncLibrary.getCompletionData2.

I am guessing, but I am wondering whether this is PMI-related (and we do have this enabled).

My knowledge of PMI is limited, as this is managed by another team.

1. Is it expected that PMI can have this sort of impact?
2. (If so) Is the only option to turn it off completely? Or are there some types of data capture that have a particularly high overhead?

Answer 1

PMI has multiple levels that can be instrumented. The basic one should have minimal impact.

This particular class that you are referring to should not be related to PMI. I am only guessing here as these classes are not exposed publicly and they are used by the WAS runtime internally.

What version of WAS are you on? There were some known issues on WAS in this space.

For e.g refer to this link below: [1]: http://www-01.ibm.com/support/docview.wss?uid=swg1PK41617 PK41617: PERFORMANCE OF THE AIO LIBRARY SUFFERS UNDER CERTAIN TYPES OF TRAFFIC FLOW

Please check if this is applicable to your environment.

Also try and skim through this link - [1]: http://www-01.ibm.com/support/docview.wss?uid=swg21366862 Disabling AIO (Asynchronous Input/Output) in WebSphere Application Server

You can probably give this a try if this is not a production environment and see if disabling AIO eliminates the spikes for you. Even if it works well, i would go through the formal IBM support process to find out exact reasons before doing the same for a production enviroment.

HTH Manglu