The PrintCompilation flag and how to read its output

Rajiv Shivane has an excellent document on his site titled "Of Thread dumps and stack traces ...". After reading his document, I ventured into some of his other writings and found the following quote here:

"The only flag I could relate to here was the -XX:+PrintCompilation. It is another thing that I have no clue how to interpret the output of this flag either! I vaguely remember reading about this in some javaOne presentation. The presenter had mentioned that it prints the methods which could not be compiled and the user can list the methods which he doesn't want to be compiled in a .hotspot_compiler file. I really wish Sun had documented these flags and their output better, instead of just mentioning "traces methods as compiled" in the VM Options document." [Rajiv Shivane - Of perf degradation with try-finallies and poor VM option docs]

Rajiv, [insert presidential voice] I feel your pain. I really do. I'm working on a document right now which will list out many JVM options and which versions (1.2.2, 1.3.1, etc.) these options are applicable to or not.

But nevertheless, lets get back to the meat of the matter, the question on -XX:+PrintCompilation. I thought that a more detailed explanation of this flags output existed somewhere on the public internet, but maybe I just can't find it today. So I'll make a small attempt to explain the output.

[read full doc here]

Comments:

Hey Moazam, Thanks for the doc! Sun should consider updating the doc at http://java.sun.com/docs/hotspot/VMOptions.html#env1 to reflect these details! I have some more queries though. Which of the flags you mention mark offending methods? I thought onStack replacement was supposed to be a good thing?! Are synchronized methods and methods with exception handlers not compiled? Would love it if you could shed some more light on the flags. Thanks! Rajiv

Posted by Rajiv Shivane on June 17, 2004 at 08:41 PM PDT #

Rajiv, I'll try to writeup something which answers some of your questions next week...I'll ping you when I post it.

Posted by Moazam on June 18, 2004 at 08:06 AM PDT #

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