Tutorial :Java out of memory Exception



Question:

I am running a Java Web Application in Tomcat. The application uses Quartz framework to schedule the cron job at regular intervals. This cron job involves parsing a 4+ MB xml file, which I am doing using JDOM API. The xml file contains around 3600 nodes to be parsed and consequently data to be updated in DB which I am doing it sequentially.
After parsing almost half of the file, my application throws a Out of Memory Exception. The stack trace of the same is :

Exception in thread "ContainerBackgroundProcessor[StandardEngine[Catalina]]" java.lang.OutOfMemoryError: Java heap space          at java.util.Arrays.copyOfRange(Arrays.java:3210)          at java.lang.String.<init>(String.java:216)          at java.lang.StringBuffer.toString(StringBuffer.java:585)          at org.netbeans.lib.profiler.server.ProfilerRuntimeMemory.traceVMObjectAlloc(ProfilerRuntimeMemory.java:170)          at java.lang.Throwable.getStackTraceElement(Native Method)          at java.lang.Throwable.getOurStackTrace(Throwable.java:590)          at java.lang.Throwable.getStackTrace(Throwable.java:582)          at org.apache.juli.logging.DirectJDKLog.log(DirectJDKLog.java:155)          at org.apache.juli.logging.DirectJDKLog.error(DirectJDKLog.java:135)          at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1603)          at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1610)          at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1590)          at java.lang.Thread.run(Thread.java:619)  Exception in thread "*** JFluid Monitor thread ***" java.lang.OutOfMemoryError: Java heap space          at java.util.Arrays.copyOf(Arrays.java:2760)          at java.util.Arrays.copyOf(Arrays.java:2734)          at java.util.Vector.ensureCapacityHelper(Vector.java:226)          at java.util.Vector.add(Vector.java:728)          at org.netbeans.lib.profiler.server.Monitors$SurvGenAndThreadsMonitor.updateSurvGenData(Monitors.java:230)          at org.netbeans.lib.profiler.server.Monitors$SurvGenAndThreadsMonitor.run(Monitors.java:169)  Nov 30, 2009 2:22:05 PM org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor processChildren  SEVERE: Exception invoking periodic operation:  java.lang.OutOfMemoryError: Java heap space          at java.lang.StringCoding$StringEncoder.encode(StringCoding.java:232)          at java.lang.StringCoding.encode(StringCoding.java:272)          at java.lang.String.getBytes(String.java:946)          at java.io.UnixFileSystem.getLastModifiedTime(Native Method)          at java.io.File.lastModified(File.java:826)          at org.apache.catalina.startup.HostConfig.checkResources(HostConfig.java:1175)          at org.apache.catalina.startup.HostConfig.check(HostConfig.java:1269)          at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:296)          at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:118)          at org.apache.catalina.core.ContainerBase.backgroundProcess(ContainerBase.java:1337)          at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1601)          at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1610)          at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1590)          at java.lang.Thread.run(Thread.java:619)  ERROR [JobRunShell]: Job updateVendorData.quoteUpdate threw an unhandled Exception:  java.lang.OutOfMemoryError: Java heap space          at java.util.Arrays.copyOfRange(Arrays.java:3210)          at java.lang.String.<init>(String.java:216)          at java.lang.StringBuffer.toString(StringBuffer.java:585)          at org.apache.commons.dbcp.PoolingConnection$PStmtKey.hashCode(PoolingConnection.java:296)          at java.util.HashMap.get(HashMap.java:300)          at org.apache.commons.pool.impl.GenericKeyedObjectPool.decrementActiveCount(GenericKeyedObjectPool.java:1085)          at org.apache.commons.pool.impl.GenericKeyedObjectPool.returnObject(GenericKeyedObjectPool.java:882)          at org.apache.commons.dbcp.PoolablePreparedStatement.close(PoolablePreparedStatement.java:80)          at org.apache.commons.dbcp.DelegatingStatement.close(DelegatingStatement.java:168)          at com.netcore.smsapps.stock.db.CompanyDaoImpl.updateCompanyQuote(CompanyDaoImpl.java:173)          at com.netcore.smsapps.stock.vendor.MyirisVendor.readScripQuotes(MyirisVendor.java:159)          at com.netcore.smsapps.stock.update.StockUpdateData.execute(StockUpdateData.java:38)          at org.quartz.core.JobRunShell.run(JobRunShell.java:207)          at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:525)  DEBUG [ExceptionHelper]: Detected JDK support for nested exceptions.  ERROR [ErrorLogger]: Job (updateVendorData.quoteUpdate threw an exception.  org.quartz.SchedulerException: Job threw an unhandled exception. [See nested exception: java.lang.OutOfMemoryError: Java heap space]          at org.quartz.core.JobRunShell.run(JobRunShell.java:216)          at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:525)  Caused by: java.lang.OutOfMemoryError: Java heap space          at java.util.Arrays.copyOfRange(Arrays.java:3210)          at java.lang.String.<init>(String.java:216)          at java.lang.StringBuffer.toString(StringBuffer.java:585)          at org.apache.commons.dbcp.PoolingConnection$PStmtKey.hashCode(PoolingConnection.java:296)          at java.util.HashMap.get(HashMap.java:300)          at org.apache.commons.pool.impl.GenericKeyedObjectPool.decrementActiveCount(GenericKeyedObjectPool.java:1085)          at org.apache.commons.pool.impl.GenericKeyedObjectPool.returnObject(GenericKeyedObjectPool.java:882)          at org.apache.commons.dbcp.PoolablePreparedStatement.close(PoolablePreparedStatement.java:80)          at org.apache.commons.dbcp.DelegatingStatement.close(DelegatingStatement.java:168)          at com.netcore.smsapps.stock.db.CompanyDaoImpl.updateCompanyQuote(CompanyDaoImpl.java:173)          at com.netcore.smsapps.stock.vendor.MyirisVendor.readScripQuotes(MyirisVendor.java:159)          at com.netcore.smsapps.stock.update.StockUpdateData.execute(StockUpdateData.java:38)          at org.quartz.core.JobRunShell.run(JobRunShell.java:207)  

This causes even my tomcat to crash. Can you please help me in diagnosing the problem. I even have enabled profiling in the Netbeans for the same but it seems that even that crashed. I have kept the default memory allocated to Tomcat. Is there any memory leak taking place. My DB is postgres and JDK is 1.6.0_15.

Thanks, Amit


Solution:1

Try increasing the ram allocation for your JVM. It should help.

Fix for eclipse: You can configure this in eclipse preference as follows

  1. Windows -> Preferences ( on mac its: eclipse ->preferences)
  2. Java -> Installed JREs
  3. Select the JRE and click on Edit
  4. on the default VM arguments field type in -Xmx1024M. (or your memory preference,for 1 gb of ram its 1024)
  5. Click on finish or OK.


Solution:2

Everytime you use a DOM to parse a XML file, you'll load entire file into memory and DOM infrastructure will use about same size to handle it, so it'll consume about twice memory than your file size.

You'll need to use SAX, an event based parser. While this can be hard to understand it first time, it's a very memory effective, as it just keeps in memory current parsing node.

Seems Java have some SAX implementations, like StAX, I hope it helps.


Solution:3

Try increasing the ram allocation for your JVM. It should help.

Fix for eclipse: You can configure this in eclipse preference as follows

Windows -> Preferences ( on mac its: eclipse ->preferences) Java -> Installed JREs Select the JRE and click on Edit on the default VM arguments field type in --Xms256m -Xmx512m -XX:MaxPermSize=512m -XX:PermSize=128m. (or your memory preference,for 1 gb of ram its 1024) Click on finish or OK.


Solution:4

Parsing XML is an fairly expensive task. The average DOM parser would already need at least five times of the memory space as the XML document big is. You should take this fact into account as well. To ensure that there is no memory leak somewhere else which caused the memory shortage for the XML parser, you really need to run a profiler. Give it all more memory, double the available memory and profile it. When you've nailed the cause down and fixed the leak, then you can just fall back to the "default" memory and retest. Or if there is really no means of any leak, then just give it all a bit more memory than default so that it all suits.

You can also consider to use a more memory efficient XML parser instead, for example VTD-XML (homepage here, benchmarks here).


Solution:5

You have to allocate more space to the PermGenSpace of the tomcat JVM.

This can be done with the JVM argument : -XX:MaxPermSize=128m

By default, the PermGen space is 64M (and it contains all compiled classes, so if you have a lot of jar (classes) in your classpath, you may indeed fill this space).

On a side note, you can monitor the size of the PermGen space with JVisualVM and you can even inspect its content with YourKit Java Profiler


Solution:6

Have you tried setting the max heap size bigger to see if the problem still occurs then? There may not even be a leak at all. It might just be that the default heap size (64m on Windows I think) is insufficient for this particular process.

I find that I almost always need to give any application I'm running Tomcat more heap and perm gen space than the defaults or I'll run into out of memory problems. If you need help adjusting the memory settings take a look at this question.


Solution:7

Are you sure there are no recursive array copy somewhere, left there by mistake? Perhaps in different threads?


Solution:8

I'll second that point about the file and the DOM taking up a great deal of memory. I also wonder when I see this:

ERROR [JobRunShell]: Job updateVendorData.quoteUpdate threw an unhandled Exception:        java.lang.OutOfMemoryError: Java heap space      at java.util.Arrays.copyOfRange(Arrays.java:3210)  

What's that copying doing? I wonder if there's something else bad going on in your code.

If you've gotten this far, it suggests that you've read the file and the DOM successfully and you're starting to write to the database. The file memory should already be reclaimed.

I'd suggest looking at memory using VisualGC so you can see what's going on.


Solution:9

You could run your application with: -XX:+HeapDumpOnOutOfMemoryError. This will cause the JVM to produce a heap dump when it runs out of memory. You can the use something like: MAT or JHAT to see what objects are being held on to. I suggest using the eclipse memory analyzer tool (MAT) on the generated heap dump as it is fairly straightforward to use: http://www.eclipse.org/mat/

Of course you will need to have some idea as to what objects may be hanging around in order for this to be useful. DOM objects? Resources from previous loads of xml documents? Database connections? MAT will allow you to trace the references back to a root object from some object that you suspect should have been garbage collected.


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