We have an application which is deployed to a WebSphere server running on UNIX, and we are experiencing two issues:
a system hang which recovers after a few minutes - to investigate, we will need the thread dump (javacore).
a system hang which does not recover and requires WebSphere to be restarted - to investigate, we will need the thread dump and heap dump.
The problem is: when a system hang occurs, we do not know whether it is issue 1 or 2.
Ideally we would like to manually generate the thread dump first, and wait to see if the system recovers. If it does not, then we generate the thread dump and the heap dump, before restarting WebSphere.
I know about the kill -3 (or kill -QUIT) command. The command would generate thread dump only (if the parameter IBM_HEAPDUMP=false), or thread dump and heap dump (if IBM_HEAPDUMP=true). However, IBM_HEAPDUMP has to be set before WebSphere is started and cannot be changed while WebSphere is running.
Is my understanding correct, regarding the IBM_HEAPDUMP parameter and the kill -3 command?
Also, is it possible get the logs in the way I described? (i.e. when generating JVM diagnostics, choose whether to generate heap dump or not on the fly)
Your understanding is consistent with everything I've read.
However, I believe you can accomplish what you want by using wsadmin scripting. This article describes how to force javacores and heapdumps on a Windows platform where kill -3 is not available, but the same commands can be run on any WebSphere system.
From within wsadmin or a wsadmin script, execute:
set jvm [$AdminControl completeObjectName type=JVM,process=server1,*]
$AdminControl invoke $jvm generateHeapDump
$AdminControl invoke $jvm dumpThreads
Related
I have a multithreaded process running on RHEL6.x (64bit).
I find that the process hangs and some threads (of the same process) crash most of the time when I try to bring up the process. Some threads wait for shared memory between the threads to get created (I can see that all of it does not get created).
But when I use strace , the process does not hang and it works just fine (all of the memory that is supposed to be created, gets created). Even interrupting strace after the memory gets created, keeps the process running fine for good.
I have read this:
strace fixes hung process
which did give me an idea. But I am still unclear on this as the version of RHEL that they have used is not mentioned.
Also, another point is that, changing the kernel to a fedora (compatible) kernel did not produce the issue.
So, I would just like to know how exactly does strace affect a process ? (or is it just the stack that moves back to the kernel as pointed out in the link) ?
We have a process (written in c++ /managed), which receives network data via tcpip.
After running the process for a while while tracking network load, it seems that network get into freeze state and the process does not getting data, there are other processes in the system that using networking (same nic) which operates normally.
the process gets out of this frozen situation by itself after several minutes.
Any idea what is happening?
Any counter i can track to see if my process reach some limitations ?
It is going to be very difficult to answer specifically,
-- without knowing what exactly is your process/application about,
-- whether it is a network chat application, or a file server/client, or ......
-- without other details about your process how it is implemented, what libraries it uses, if relevant to problem.
Also you haven't mentioned what OS and environment you are running this process under,
there is very little anyone can help . It could be anything, a busy wait loopl in your code, locking problems if its a multi-threaded code,....
Nonetheless , here are some options to check:
If its linux try below commands to debug and monitor the behaviour of the process and see what could be problem-
top
Check top to see ow much resources(CPU, memory) your process is using and if there is anything abnormally high values in CPU usage for it.
pstack
This should stack frames of the process executing at time of the problem.
netstat
Run this with necessary options (tcp/udp) to check what is the stae of the network sockets opened by your process
gcore -s -c
This forces your process to core when the mentioned problem happens, and then analyze that core file using gdb
gdb
and then use command where at gdb prompt to get full back trace of the process (which functions it was executing last and previous function calls.
I want to check the memory usage of a JAR that does some calculations. For this I want to use JVM monitor. When starting JVM monitor, I need to pick the JVM that is running my jar. But the problem is that my JAR executes so fast (<1sec) that it never shows up in the list..
Is there any way I can start the JVM without executing the JAR immediatly?
JConsole finds running applications at the time when JConsole starts . Then only the currently running applications port and host will be displayed in the list. But for such very short running applications to be shown in the list adding a wait at the end of program execution is the only choice you can do .
Also whatever the memory stats Jconsole will display will include Jconsole's memory footprint as well. So the better choice for monitoring is jvisualvm which can show memory , threads and gc statistics as well .
Alternatevely if you want to check the code cache or compilation statistics you can use -XX:+LogCompilation -XX:+UnlockDiagnosticVMOptions -XX:+PrintCodeCache
I need to implement (in Qt) some solution to communicate between two programs running on Linux machine. One program is Worker, and the second is Watchdog. Basically I need Watchdog to periodically check on Worker and in case something wrong (no process,hangup - no answer from Worker) kill Worker (if present) and start it again.
Worker runs as a daemon, so I think starting it from unix /etc/init.d/worker would be appropriate.
I can see two solutions
Unix signals - both of them can send and receive Unix SIGUSR1
Shared memory
Which one to choose?
With signals both of programs will have to know others pid, probably reading from filesystem /var/run so it looks like a drawback.
With shared memory, all I need is "key" that programs will have hardcoded, so no need to read pids from filesystem. Since Watchdog should start first it can create shared mem segment, and Worker will only attach to it and maybe update its timestamp value??? However, to stop Worker by Watchdog (in case of hungup) Watchdog will still need Worker pid to send him SIGKILL, maybe it can read it from shared mem? Both concepts are new to me.
So what is the proper way to build reliable Watchdog, or am I missing something?
best regards
Marek
I think this is the best solution available through Qt:
http://qt-project.org/doc/qt-4.8/qlocalsocket.html
http://qt-project.org/doc/qt-4.8/qlocalserver.html
The QLocalSocket class provides a local socket. On Windows this is a
named pipe and on Unix this is a local domain socket.
http://qt-project.org/doc/qt-4.8/ipc-localfortuneserver.html
http://qt-project.org/doc/qt-4.8/ipc-localfortuneclient.html
Hope that helps.
On my machine (XP, 64) the ASP.net worker process (w3wp.exe) always launches with 5.5GB of Virtual Memory reserved. This happens regardless of the web application it's hosting (it can be anything, even an empty web page in aspx).
This big old chunk of virtual memory is reserved at the moment the process starts, so this isn't a gradual memory "leak" of some sort.
Some snooping around with windbg shows that the memory is question is Private, Reserved and RegionUsageIsVAD, which indicates it might be the work of someone calling VirtualAlloc. It also shows that the memory in question is allocated/reserved in 4 big chunks of 1GB each and a several smaller ones (1/4GB each).
So I guess I need to figure out who's calling VirtualAlloc and reserving all this memory. How do I do that?
Attaching a debugger to the process prior to the memory allocation is tricky, because w3wp.exe is a process launched by svchost.exe (that is, IIS/ASP.Net filter) and if I try to launch it myself in order to debug it it just closes down without all this profuse memory reservation. Also, the command line parameters are invalid if I resuse them (which makes sense because it's a pipe created by the calling process).
I can attach windbg it to the process after the fact (which is how I found the memory regions in question), but I'm not sure it's possible at that point to determine who allocated what.
David Wang answers this to a similar question:
[...] the ASP.Net performance developer tells me that:
The Reserved virtual memory is nothing to worry about. You can view
it as performance/caching prerequisite
of the CLR. And heavy load testing
shows that it is nothing to worry
about.
System.Windows.Forms - It's not pulled in by empty hello world ASPX
page. You can use Microsoft Debugging
Tools and "sx e ld
system.windows.forms" to identify what
is actually pulling it in at runtime.
Or you can ildasm to find the
dependency.
mscorlib - make sure it is GAC'd and NGen'd properly.
Virtual memory is just the address space allocated to the process. It has nothing to do with memory usage.
See:
Virtual Memory
Pushing the Limits of Windows: Virtual Memory
http://support.microsoft.com/kb/555223
Reserved memory is very different from allocated memory. Reserving memory just allocates address space. It doesn't commit any physical pages.
This address space is likely allocated by IIS for its heap. It will only commit pages when needed.
If you really want to launch w3wp.exe from windbg, you probably need to launch it with valid command-line arguments. You can use Process Explorer to determine what the command line for the current w3wp.exe process is. For instance, on my server, mine was:
c:\windows\system32\inetsrv\w3wp.exe -a \.\pipe\iisipmeca56ca2-3a28-452a-9ad3-9e3da7b7c765 -t 20 -ap "DefaultAppPool"
I'm not sure what the UID in there specifies, but it looks it's probably generated on the fly by the W3SVC service (which is what launched w3wp.exe) to name the pipe specified there. So you should definitely look at your command line before launching w3wp from windbg.