Garbage collection in java, JAVA Programming

The Java programming language is object-oriented and includes automatic garbage collection. Garbage collection is the process of reclaiming memory taken up by unreferenced objects.

Memory Management, Java and Impact on Application Servers

The task of memory management that was always challenging with compiled object-oriented languages such as C++. On the other hand, Java is an interpretive language that takes this memory management out of the hands of developers and gives it directly to the virtual machine where the code will be run. This means that for best performance and stability, it is critical that the Java parameters for the virtual machine be understood and managed by the Application Server deployment team. This section will describe the various parts of the Java heap and then list some useful parameters and tuning tips for ensuring correct runtime stability and performance of Application Servers.

Java Virtual Machines

The Java specification as to what is “standard” for a given release is written and maintained by the JavaSoft division of Sun Microsystems. This specification is then delivered to other JVM providers (IBM, HP, etc). JavaSoft provides the standard implementation on Windows, Solaris, and LINUX. Other platforms are required to deliver the code functionality but their JVM options can be different. Java options that are preceded with “-X” or “-XX” are typically platform-specific. That being said, many options are used on all platforms. One must read in detail the README notes from the various releases on various platforms to be kept up-to-date with the variations. This guide will mention the most critical ones and distinguish between those which are implemented on most platforms and those which are platform-specific.

The Java Heap

The Java heap is divided into three main sections: Young Generation, Old Generation and the Permanent Generation as shown in the figure below.

 

Also, not shown here, is another area called the Code Cache which is typically about 50Mb in Size.

 

HotSpot VM

 

The HotSpot VM is the garbage collector that comes with the JavaSoft virtual machine. Its specification is delivered to all JVM providers (HP, IBM, BEA, etc) and the standard implementation is deployed by JavaSoft on Solaris, Windows and LINUX.

 

Default Garbage Collection Algorithms

 

Scavenge Garbage Collection

 

Scavenge Garbage Collection (also known as a Minor Collection) occurs when the Eden Space is full. By default, it is single-threaded but does not interrupt the other threads working on objects. It can be parallelized starting at Java 1.4 but if too more ParallelGCThreads are specified than CPU cores where the JVM is running, this can cause bottlenecks. For this reason, it is suggested to be careful in when and where to use the parallel options. These will be discussed further on.

 

Full Garbage Collection

 

A Full Garbage Collection (FullGC) occurs under these conditions:

 

The Java application explicitly calls System.gc(). This can be avoided by implementing the -

 

XX:+DisableExplicitGC parameter in the startup command for all Application Server JVMs (Tomcat,Application Server JVM, etc.)

Posted Date: 9/21/2012 3:48:24 AM | Location : United States







Related Discussions:- Garbage collection in java, Assignment Help, Ask Question on Garbage collection in java, Get Answer, Expert's Help, Garbage collection in java Discussions

Write discussion on Garbage collection in java
Your posts are moderated
Related Questions
What do you mean through FTP or File Transfer Protocol? FTP: File transfer protocol was first introduced in the year of 1973; it standardized the transfer of files among comp

write a program in java which enters name,roll #,and shows the sum of students english and maths marks?

How to Implementing the Cloneable Interface The java.lang.Object class contains a clone() method which returns a bitwise copy of the current object. protected native Object cl

How to Returning Multiple Values From Methods ? It is not probable to return more than one value from techniques. You cannot, for example, return the licensePlate, speed and m


write a program that count the number of occurences of string in the n-th padovan string p(n)   program in java // aakash , suraj , prem sasi kumar kamaraj college progr

The JMS provider handles security of the messages, data conversion and the client triggering. The JMS provider verifies the level of encryption and the security level of the messag

We require expert programmers who will solve problems, who can code by the book, and who will code in java and JavaScript what is designed. Skills required: CSS, Java, HTML5,

what is the use of design pattern in java ?

Explain Overriding Methods: The Solution The object oriented solution to this problem is to describe a new class, call it SlowCar, that inherits from Car and imposes the additi