Thank you guys for useful comments. I just fixed the issue.
Indeed, each child task has its own JVM and I need to pass -agentlib when they are spawned.
This can be done by adding the following in mapred-site.xml in hadoop. 
(The configuration is only effective for the child JVMs spawned by TaskTracker.)
<property>                                                                                                                                                                                
    <name>mapred.child.java.opts</name>                                                                                                                                                   
    <value>-agentlib:jvmti_oprofile</value>                                                                                                                                    
</property>   

Thanks again for the helps.

Tommy



On Fri, Aug 15, 2014 at 8:55 AM, Maynard Johnson <maynardj@us.ibm.com> wrote:
On 08/14/2014 06:09 PM, Tommy wrote:
> Hi,
>
> I am trying to profile mapreduce task using operf.
> I have some troubles with getting correct symbols of java threads.
>
> What I did was to operf the tasktracker which spawns map and reduce tasks (threads).
> I did like the following to start the tasktracker.
> *operf /usr/lib/jvm/java-oracle/bin/java -agentlib:jvmti_oprofile ......*
>
> However, only the tasktracker thread gets the correct symbols for all addresses. I found that only one ".jo" file is created for the tasktracker, not the child threads that inherit the tasktracker, such as map and reduce tasks. All the child threads get "anon".
It sounds like some additional JVMs are being spawned . . . so you need to be sure to pass the -agentlib on those invocations. And how that can be done is not something we can help with.  It requires knowledge of the application structure.

-Maynard
>
> Please help me to resolve the issue.
> Thank you very much.
>
> Tommy
>
>
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