24

I realize that Java code will slow down when run in debugger.

Question is, will the code slow down simply by starting Java with these options:

Xdebug -Xrunjdwp:transport=dt_socket,address=5005,server=y,suspend=n

??

Or does the slowdown only happen when you connect to the "debug port" and actually step through code using an IDE?

Improve this question

3 Answers 3

Reset to default
17

First, to strictly answer your question - at least as stated in its title - -Xdebug only enables debugging support in the VM using JVMDI in JVMs prior to 5.0. So in itself, it doesn't do much. Moreover, JVMDI is deprecated since 5.0 in favor of JVMTI:

-Xdebug
Start with support for JVMDI enabled. JVMDI has been deprecated and is not used for debugging in J2SE 5.0, so this option isn't needed for debugging in J2SE 5.0.

So -Xdebug doesn't do anything anymore and the important part is:

-Xrunjdwp:<name1>[=<value1>],<name2>[=<value2>]...

or, starting with Java 5.0, the newer (that you should prefer as the JDWP agent in 5.0 uses the JVM TI interface to the VM rather than the older JVMDI interface):

--agentlib:jdwp=<name1>[=<value1>],<name2>[=<value2>]...

Now, to my knowledge, just loading the jwdp agent and/or configuring the JVM to listen for a socket connection on a given port don't have any noticeable performance impact. But connecting a debugger does.

Improve this answer
Sign up to request clarification or add additional context in comments.

2 Comments

Even loading the jwdp agent without attaching a debugger can have a performance penalty.
There is an opposite opinion stackoverflow.com/a/2195731/657723
11

Performance testing results at AMD indicate that simply enabling the debug agent via the JVM commandline does cause performance degradation regardless of having a debugger connected to it, and that the degradation can be quite large depending on the workload:

Note that we weren’t actually attaching a debugger when we were measuring performance, so we had assumed this agentlib option would be performance-neutral in this usage scenario. When we removed this option, both the CPU utilization and the performance on this workload (measured in requests handled per second) improved dramatically.

See their report:

http://developer.amd.com/resources/documentation-articles/articles-whitepapers/java-performance-when-debugging-is-enabled/

Above link is dead, here's a web archive link of it: https://web.archive.org/web/20160316201129/http://developer.amd.com/resources/documentation-articles/articles-whitepapers/java-performance-when-debugging-is-enabled/

Improve this answer

2 Comments

When the JVM process runs for long (some days/weeks), slow down is definitely visible. My context: GWT application with Oracle backend, Java 7 on Solaris Zone.
The AMD article has dropped off the web, but can stil be found in the wayback machine here : web.archive.org/web/20160316201129/http://developer.amd.com/…
1

No, simply enabling the debugging port will have no effect on runtime performance. At least I've never noticed any.

..

Improve this answer

7 Comments

that's not the question he is asking, he's talking about launching the JVM with debug options
@Valentin - huh? What? Please explain why the command lines don't enable a debug port and hence answer the query.
ok, seems like I had a sudden case of "shit in my eyes"...@jarnbjo : could you just make a void edit to your answer, so I can remove my downvote ?
@Valentin No, you didn't, the initial answer was "The presence of debugging information in the class files will only increase the class file size and has no impact on runtime performance. At least not with current VMs.". This was not an answer to the question.
I did in fact misread the question and was a little bit too quick to answer, but edited my answer when I realized my mistake. I'm not sure why the edit does not show though ...
|

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.