Java garbage collection verbose not working

Question

I have specified following verbose options but JVM is not printing any GC details to the log

-XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode 
-verbose:gc  -XX:+PrintGCTimeStamps -XX:+PrintGCDetails

I am using java 1.8.0_05-b13

I tried some permutation and combination and noticed that only specifying

-verbose:gc  works and logs GC to stdout but following doesn't work

-verbose:gc  -XX:+PrintGCTimeStamps -XX:+PrintGCDetails -Xloggc:GC.log

What code did you executed? Garbage collection may occur when many instances are created and lost links to them. — Fumu 7, Nov 25 '14 at 09:04
I can see garbage collection using jconcole but no GC logging — Amrish Pandey, Nov 25 '14 at 09:34

score 0 · Answer 1 · answered Nov 25 '14 at 09:26

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The -verbose:gc switch makes the application print the GC details to stdout, so make sure that you try to read it from there. You can also use -Xloggc:gcdetails.log to print the details to an actual file instead.

answered Nov 25 '14 at 09:26

Mike Laren

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I am using log4j to redirect all stdout to a file hence i am expecting it there. Xloggc sounds like cleaner approach but i am not even getting logs on stdout – Amrish Pandey Nov 25 '14 at 09:34
Also, using jconsole I checked memory bean and its verbose attribute is false – Amrish Pandey Nov 25 '14 at 09:36
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Maybe your application is not generating enough garbage. Try launching it with very low memory values (e.g. `-Xms2m -Xmx64m`) for force GC to run. – Mike Laren Nov 25 '14 at 09:37
It is doing gc . i can see it in jconsole – Amrish Pandey Nov 25 '14 at 09:38
Can you paste the command line you're running? Maybe it's an OS-specific issue. – Mike Laren Nov 25 '14 at 09:42
Corrected my java version. It turned out to be different than expected and also added more details about subsequent test. – Amrish Pandey Nov 25 '14 at 10:23

score 0 · Answer 2 · answered Nov 25 '14 at 12:50

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Just guessing, but jconsole seems to hook into the JVM using JMX beans, while -verbose:gc simply prints directly to stdout from its C++ code and provides no access to it to Java.

Start it locally and look at the standard output to confirm or deny it.

answered Nov 25 '14 at 12:50

maaartinus

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score 0 · Answer 3 · answered Nov 25 '14 at 13:40

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GC parameters were passed as Single string to ProcessBuilder. Sending each JVM argument as separate string to ProcessBuilder fixed it.

answered Nov 25 '14 at 13:40

Amrish Pandey

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Java garbage collection verbose not working

3 Answers3