#outofmemoryerror

Memory Model of Java Virtual Machine

The Java Virtual Machine is an abstract computing machine. It is responsible for most of the features which made Java a great technology. Few of the major selling points of Java was:

Platform Independence

Hardware Independence

Operating System Independence

Security from malicious programs

It is said to be abstract computing machine because it offers all the specification which if implemented…

Resolved: What causes PermGen OutOfMemoryError on JBoss? #programming #dev #answer

What causes PermGen OutOfMemoryError on JBoss?

What is the underlying cause of a PermGen OutOfMemoryError in JBoss?

I am running JBoss AS 4.2.2 in my development environment, and this occurs after redeploying my web application a large number of times.

Christian Vest Hansen’s blog gives JVM options that help a lot, but do not solve the problem completely:

-XX:+UseConcMarkSweepGC…

One of the tools that I like to recommend to people looking to backup their data is Crashplan by Code42. It constantly works to backup all your data to the cloud for the very low price of around $5/month. There's no limit to what you can backup and no throttling. Drives that were attached to your machine once will be backed up, unlike Backblaze which deletes them after 90 days of being "offline." In short, it's awesome, except for when it crashes.

I hadn't ever seen it crash until last week. It boots as a login item, does its thing and begins to index files. It will index and index, but then just die. Fortunately, there's a very helpful Code42 support doc here. Check each service.log.# file in /Library/Logs/CrashPlan. Search the document for "OutOfMemoryError" and if you find the phrase, you'll want to increase the default amount of RAM Crashplan is provided.

The Code42 doc spells it out quite well, but you'll want to:

Stop Crashplan using sudo launchctl unload /Library/LaunchDaemons/com.crashplan.engine.plist in Terminal.

Authenticate with your Admin password

Use the following command to open the .plist file for editing sudo nano /Library/LaunchDaemons/com.crashplan.engine.plist

Arrow down to the line that says -Xmx1024m and replace it with a larger number, perhaps 2048.

Press Control + X to exit, Y to save changes and enter to write the filename.

Then Start Crashplan again using sudo launchctl load /Library/LaunchDaemons/com.crashplan.engine.plist

StringBuilder or StringBuffer are used for string manipulations. Yet they fail some times. Both the final classes are the extension for packaged scoped abstract class named "java.lang.AbstractStringBuilder". These builder/buffer classes holds character array and append or manipulate this char[] each time we perform operations on it. The default char[] size is 16 although this can be specified while creating the object. When append() method is called upon StringBuilder/StringBuffer, the capacity of this char[] is checked if the String/char/any other object can be added to ongoing char[] buffer. If the character buffer size is less. I.e. not sufficient enough to append more, the capacity is doubled . Lets say its capacity was 16, and not sufficient to add more, than the the capacity is increased by doubling the size of current buffer length. This keeps happening when you keep on appending stuffs to it. Common case is while reading a file and storing it inside memory in form of a StringBuilder. You never know what the size of file could be. when size isn't sufficient for the StringBuilder, buffer size is doubled and this keeps growing. A point will reach when System is not able to allocate enough space for the buffer.

Root cause

The problem with StringBuilder I see is it doubles the capacity from current length. Lets say the internal char buffer length is 65000 and more 100 chars has to be added than the buffer capacity is doubled to 65000 * 2. If we dive into the code of Arrays.copyOf() method line no# 2882. It tries to create a new char[] of size 65000 * 2 (in our case).

char[] copy = new char[newLength];

And this will throw Error if the Java Virtual machine does not have enough to allocate.

Solution/Fix

How do we get rid of such OutOfMemoryError? Decide what are we going to hold in StringBuilder's class buffer. It is always better to use StringBuilder/StringBuffer instead of performing string operations like

String myString = "x" + "y" + "z"

ut if we have to read some file and then write that into some file back again then, go for Streams. This is what the purpose of Streams or Writer/Reader are. Decide the buffer length and use streams to work in such cases. If that is not workable in the situation, than the common approach for solving java.lang.OutOfMemoryError is to increase the JVM memory via parameters like -Xmx256m

java.exe -Xmx256m

Conclusion:

String manipulation is always a performance over head. implement the best practices and best applicable solution as when to use normal String concatenations or go for StringBuilder or Streams

.

A mutable sequence of characters. This class provides an API compatible with StringBuffer, but with no guarantee of synchronization. This class is designed for use as a drop-in replacement for StringBuffer in places where the string buffer was being used by a single thread (as is generally the case). Where possible, it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.