Troubleshooting in Production Environments¶
The following sections will guide you to troubleshoot various issues that may arise in your Micro Integrator deployment.
Analyzing a stack trace¶
When your Java process starts to spin your CPU, you must immediately analyze the issue using the following two commands and obtain the invaluable information required to tackle the issue. This is done based on the process ID (pid).
jstack <pid> > thread-dump.txt
ps -C java -L -o pcpu,cpu,nice,state,cputime,pid,tid > thread-usage.txt
OS X users can alternatively use the command
ps M <PID>instead.
These commands provide you with the thread-dump.txt file and the thread-usage.txt file. After obtaining these two files, do the following.
Find the thread ID (the one that belongs to the corresponding PID) that takes up the highest CPU usage by examining the thread-usage.txt file.
%CPU CPU NI S TIME PID TID .......... 0.0 - 0 S 00:00:00 1519 1602 0.0 - 0 S 00:00:00 1519 1603 24.8 - 0 R 00:06:19 1519 1604 2.4 - 0 S 00:00:37 1519 1605 0.0 - 0 S 00:00:00 1519 1606 ..........
In this example, the thread ID that takes up the highest CPU usage is 1604.
Convert the decimal value (in this case 1604) to hexadecimal. You can use an online converter to do this. The hexadecimal value for 1604 is 644.
- Search the thread-dump.txt file for the hexadecimal obtained in order to identify the thread that spins. In this case, the hexadecimal value to search for is 644. The thread-dump.txt file should have that value as a thread ID of one thread.
That thread usually has a stack trace, and that's the lead you need in order to find the issue. In this example, the stack trace of the thread that spins is as follows.
"HTTPS-Sender I/O dispatcher-1" prio=10 tid=0x00007fb54c010000 nid=0x644 runnable [0x00007fb534e20000] java.lang.Thread.State: RUNNABLE at org.apache.http.impl.nio.reactor.IOSessionImpl.getEventMask(IOSessionImpl.java:139) - locked <0x00000006cd91fef8> (a org.apache.http.impl.nio.reactor.IOSessionImpl) at org.apache.http.nio.reactor.ssl.SSLIOSession.updateEventMask(SSLIOSession.java:300) at org.apache.http.nio.reactor.ssl.SSLIOSession.inboundTransport(SSLIOSession.java:402) - locked <0x00000006cd471df8> (a org.apache.http.nio.reactor.ssl.SSLIOSession) at org.apache.http.impl.nio.reactor.AbstractIODispatch.inputReady(AbstractIODispatch.java:121) at org.apache.http.impl.nio.reactor.BaseIOReactor.readable(BaseIOReactor.java:160) at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvent(AbstractIOReactor.java:342) at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvents(AbstractIOReactor.java:320) at org.apache.http.impl.nio.reactor.AbstractIOReactor.execute(AbstractIOReactor.java:280) at org.apache.http.impl.nio.reactor.BaseIOReactor.execute(BaseIOReactor.java:106) at org.apache.http.impl.nio.reactor.AbstractMultiworkerIOReactor$Worker.run(AbstractMultiworkerIOReactor.java:604) at java.lang.Thread.run(Thread.java:722)
Capturing the state of the system¶
Carbondump is a tool that is used to collect all the necessary data from a running WSO2 product instance at the time of an error. The carbondump generates a ZIP archive with the collected data that helps to analyze the system and to determine the problem that caused the error. Therefore, it is recommended that you run this tool as soon as an error occurs in the your product instance.
As with any other java product, if your WSO2 Micro Integrator cluster fails due to a resource exhaustion, the heap and thread dumps will always point you towards the cause of the leak. Therefore, it is important to be able to retrieve heap and thread dumps from an environment at the point when an error occurs. This will avoid the necessity of reproducing the exact issue again (specially, in the case of production issues). A resource exhaustion can happen for two reasons:
- Due to a bug in the system.
- An actual limitation of resources based on low configuration values.
You can easily create a heap dump and thread dump using the CarbonDump tool that is shipped with your product. These will also provide information about the product version and any patch inconsistencies.
If you are using an Ubuntu version 10.10 or above and if you get an error on being unable to attach the process, execute the following command to rectify it:
echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope
This changes the yama/ptrace_scope variable of the kernel temporarily (i.e., until the next reboot). For more information, see the Oracle documentation.
When using the tool, you have to provide the process ID (pid) of the
product instance and the
which is where your unzipped Micro Integrator distribution files reside. The
command takes the following format:
sh carbondump.sh [-carbonHome path] [-pid of the carbon instance]
sh carbondump.sh -carbonHome /home/user/wso2carbon-3.0.0/ -pid 5151
carbondump.bat -carbonHome c:\wso2carbon-3.0.0\ -pid 5151
The tool captures the following information about the system:
- Operating system information (kernel version)
- Installed modules lists and their information
- List of running tasks in the system
- Memory information of the Java process (Java heap memory dump)
- Histogram of the heap
- Objects waiting for finalization
- Java heap summary. GC algo used, etc.
- Statistics on permgen space of Java heap
- Information about the running Micro Integrator instance (Product name and
- Carbon framework version (This includes the patched version)
- MI_HOME, JAVA_HOME
- Configuration files
- Log files
- H2 database files
- Thread dump
- Checksum values of all the files found in the MI_HOME.
Viewing process threads in Solaris¶
This information is useful to understandand whether the database processes are not fully utilizing the CPU's threading capabilities. It gives you a better understanding on how 11g and 10g takes advantage of threading and how you can validate those queries from the system.
The following information provides insight on whether a Solaris process is parallelized and is taking advantage of the threading within the CPU.
- Open a command line in Solaris.
prstatand have a look to the last column, labeled
PROCESS/NLWP. NLWP is a reference to the number of lightweight processes and are the number of threads the process is currently using with Solaris as there is a one-to-one mapping between lightweight processes and user threads. A single thread process will show
1there while a multi-threaded one will show a larger number. See the following code block for an example.
PID USERNAME SIZE RSS STATE PRI NICE TIME CPU PROCESS/NLWP ... 12905 root 4472K 3640K cpu0 59 0 0:00:01 0.4% prstat/1 18403 monitor 474M 245M run 59 17 1:01:28 9.1% java/103 4102 oracle 12G 12G run 59 0 0:00:12 4.5% oracle/1
If you observe the
PROCESS/NLWPvalue in the example above, you can identify that
oracleare single thread processes, while
javais a multi-threaded process.
Alternatively, you can analyze individual thread activities of a multi-threaded process by using the
-poptions such as
prstat -L -p pid. This displays a line for each thread sorted by the CPU activity. In that case, the last column is labeled
PROCESS/LWPID, where LWPID is the thread ID. If more than one thread shows significant activity, your process is actively taking advantage of multi-threading.