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
State about the JVM? JVM is the acronym which stands for 'Java virtual machine'. JVM provides execution environment. JVM isn't platform independent. JVM is Java

examples of 2D arrays

In  order  to  provide  portable  and  reliable  EJB  elements,  the  following  restrictions  apply  to  EJB  code implementation: 1. Avoid using static non-final fields. Defin

Explain Labeled Loops in details ? Generally inside nested loops break and continue exit the innermost enclosing loop. For instance consider the subsequent loops. for (int i=1

This assignment is a good project for working with 2 dimensional arrays. In this program, you will implement an ascii version of the classic game "Connect 4". Connect 4 is a 2 p

The last exercise of each assignment will be continuous from assignment to assignment and will have the goal of building an e-store website by the end of the course. Date & Tim

I am requiring webcam software integrated into my site I have website and I am wanting webcam software integrated into my site the company I have found doesn't offer support in

The purpose of this assignment is to help you learn the Java environment and practice I/O instructions, assignment, and simple arithmetic operators. Teams: The assignment can