WebSphere Application Server - Garbage Collection

Author

Garbage Collection

2006-04-11, 10:17 am

I have enabled Garbage Collection on WebSphere Application Server V6.0 in Microsoft Windows 2000 Server.

I got the following output in "native_stderr.log" file :-

[ JVMST080: verbosegc is enabled ]
[ JVMST082: -verbose:gc output will be written to stderr ]
<GC[0]: Expanded System Heap by 65536 bytes
<GC[0]: Expanded System Heap by 65536 bytes

<AF[34]: Allocation Failure. need 14920 bytes, 214412 ms since last AF>
<AF[34]: managing allocation failure, action=1 (168048/135247064) (1213328/1656104)>
<GC(34): GC cycle started Wed Apr 05 14:38:28 2006
<GC(34): freed 48819664 bytes, 36% free (50201040/136903168), in 177 ms>
<GC(34): mark: 137 ms, sweep: 40 ms, compact: 0 ms>
<GC(34): refs: soft 0 (age >= 32), weak 0, final 4518, phantom 2>
<AF[34]: completed in 177 ms>

Can you please guide me what exactly output is showing?
Is it memory management required? Is their any memory bottlenecks?

Please help to understand this issue.
vaze

Ken Hygh

2006-04-11, 10:17 am

vazeamit@hotmail.com wrote:
> I have enabled Garbage Collection on WebSphere Application Server V6.0 in Microsoft Windows 2000 Server.
>
> I got the following output in "native_stderr.log" file :-
>
> [ JVMST080: verbosegc is enabled ]
> [ JVMST082: -verbose:gc output will be written to stderr ]
> <GC[0]: Expanded System Heap by 65536 bytes
> <GC[0]: Expanded System Heap by 65536 bytes
>
> <AF[34]: Allocation Failure. need 14920 bytes, 214412 ms since last AF>
> <AF[34]: managing allocation failure, action=1 (168048/135247064) (1213328/1656104)>
> <GC(34): GC cycle started Wed Apr 05 14:38:28 2006
> <GC(34): freed 48819664 bytes, 36% free (50201040/136903168), in 177 ms>
> <GC(34): mark: 137 ms, sweep: 40 ms, compact: 0 ms>
> <GC(34): refs: soft 0 (age >= 32), weak 0, final 4518, phantom 2>
> <AF[34]: completed in 177 ms>
>
> Can you please guide me what exactly output is showing?
> Is it memory management required? Is their any memory bottlenecks?
>
> Please help to understand this issue.
> vaze

You should be able to find loads of stuff on analyzing verbosegc output
on google.

Analyzing the output without the appserver under load is meaningless
however. And, since it's been over 3 minutes (214412 milliseconds) since
the last Allocation Failure, I'd hazard a guess that your server isn't
under load.

Ken

Ben_

2006-04-11, 10:17 am

For in-depth technical details, see IBM JVM Diagnostics Guide
(http://www.ibm.com/developerworks/java/jdk/diagnosis).

To make nice drawing of the data, use Diagnostic Tool for Java Garbage
Collector (http://www.alphaworks.ibm.com/tech/gcdiag)

As Ken pointed out, be sure to analyze it when the application is at a
steady state.

And don't be frightened by the wording: "allocation failure" does not mean
there was an error in the application, it just means GC noticed it has to
run.

SaketR

2006-04-11, 10:17 am

Also see,

http://www-128.ibm.com/developerwor...ary/i-garbage1/
http://www-128.ibm.com/developerwor...ary/i-garbage2/
http://www-128.ibm.com/developerwor...i-garbage3.html

http://www-128.ibm.com/developerwor...rary/i-gctroub/

http://www-128.ibm.com/developerwor...0&Search=Search

Regards,
Saket

<vazeamit@hotmail.com> wrote in message
news:1734198225.1144229346722.JavaMail.wassrvr@ltsgwas007.sby.ibm.com...
>I have enabled Garbage Collection on WebSphere Application Server V6.0 in
>Microsoft Windows 2000 Server.
>
> I got the following output in "native_stderr.log" file :-
>
> [ JVMST080: verbosegc is enabled ]
> [ JVMST082: -verbose:gc output will be written to stderr ]
> <GC[0]: Expanded System Heap by 65536 bytes
> <GC[0]: Expanded System Heap by 65536 bytes
>
> <AF[34]: Allocation Failure. need 14920 bytes, 214412 ms since last AF>
> <AF[34]: managing allocation failure, action=1 (168048/135247064)
> (1213328/1656104)>
> <GC(34): GC cycle started Wed Apr 05 14:38:28 2006
> <GC(34): freed 48819664 bytes, 36% free (50201040/136903168), in 177 ms>
> <GC(34): mark: 137 ms, sweep: 40 ms, compact: 0 ms>
> <GC(34): refs: soft 0 (age >= 32), weak 0, final 4518, phantom 2>
> <AF[34]: completed in 177 ms>
>
> Can you please guide me what exactly output is showing?
> Is it memory management required? Is their any memory bottlenecks?
>
> Please help to understand this issue.
> vaze