Skip to main content

Concluding the series on Java garbage collection

Over the past few blog posts we have covered some basics of garbage collection in Java. Garbage collection is a key strength of the JVM, since we do not have to worry about releasing object memory. It reduces memory leaks and other problems associated with improper memory management code that often creeps in when we program against hard deadlines :-)

However, for large programs we very often have to tweak the default garbage collection mechanism to improve performance. Here's a nice article that explains garbage collection in much more detail with good examples. This page contains several links to memory management in the Java Hotspot VM. Here's another page that explains how to fine tune the Java garbage collector in Java 1.5.

It is also a good idea to keep up with the latest in technology, so here's a page that describes enhancements to the Java VM in version 1.6, that influence the garbage collector.

I hope you enjoyed this series. Over the next few months I hope to cover various aspects of core Java through such mini series posts. I hope you find them informative. As always your comments and suggestions are very welcome.

You can discuss this post in our learning forum.

Note: This text was originally posted on my earlier blog at
Here are the comments from the original post

AUTHOR: Sanket Daru
DATE: 06/29/2007 05:13:19 AM
Dear Sir,
Indeed the mini-series on JVM Garbage Collection was very informative. At the conclusion, I have one question though.

Well this might be out of scope of the mini-series, but I want some guide. I was working with XML parsing in Java and started off using DOM parsing. Now DOM has its limitations, mainly due to its HEAVY footprint and it ends up giving me "out of memory" errors... I tried several other means but nothing seemed to work out...

Eventually I left the matter because I was just trying it out for experimentation. I had decided to use SAX due to its light footprint and event-based modeling.

Now my question is, can we tweak memory management of JVM and Garbage Collector programatically? Such a solution will be really helpful.

Looking forward to more of such informative mini-series...

DATE: 06/29/2007 06:52:47 AM
Hi Sanket,

As of now I do not believe there is a way to "programatically" tweak garbage collection. You can tweak the JVM when you start it using:
-Xms -Xmx for heap size.
Using various other options as described in (, you can modify the generation sizes and ask the JVM to use a particular JVM algorithm.

However, all these things have to be done when the JVM is started.

Increasing the heap size will allow you to hold a larger DOM tree in memory, but tweaking the GC will only help you with performance, not with being able to hold more objects in memory.

One potential solution might be to use serialization. If you can hold only enough information in the nodes such that your entire tree can live in memory, and when a node is visited it's details are retrieved from a serialized object. Once you navigate away from that node release the memory (modifying the serialized object of any changes are made).

I am not sure of this is a standard way of dealing with this problem and if an API already exists to achieve it. But it seems like a plausible solution.


Popular posts from this blog

Running your own one person company

Recently there was a post on PuneTech on mom's re-entering the IT work force after a break. Two of the biggest concerns mentioned were : Coping with vast advances (changes) in the IT landscape Balancing work and family responsibilities Since I have been running a one person company for a good amount of time, I suggested that as an option. In this post I will discuss various aspects of running a one person company. Advantages: You have full control of your time. You can choose to spend as much or as little time as you would like. There is also a good chance that you will be able to decide when you want to spend that time. You get to work on something that you enjoy doing. Tremendous work satisfaction. You have the option of working from home. Disadvantages: It can take a little while for the work to get set, so you may not be able to see revenues for some time. It takes a huge amount of discipline to work without a boss, and without deadlines. You will not get the benefits (insuranc

Testing Groovy domain classes

If you are trying to test Grails domain class constraints by putting your unit test cases in the 'test/unit' directory, then your tests will fail because the domain objects will not have the 'valdate' method. This can be resolved in two ways: Place the test cases inside test/integration (which will slow things down) Use the method 'mockForConstraintsTests(Trail)' to create mock method in your domain class and continue writing your test cases in 'test/unit' What follows is some example code around this finding. I am working on a Groovy on Grails project for a website to help programmers keep up and refresh their skills. I started with some domain classes and then moved on to write some unit tests. When we create a Grails project using grails create-app , it creates several directories, one of which is a directory called 'test' for holding unit tests. This directory contains two directories, 'unit', and 'integration' for unit and

Planning a User Guide - Part 3/5 - Co-ordinate the Team

Photo by  Helloquence  on  Unsplash This is the third post in a series of five posts on how to plan a user guide. In the first post , I wrote about how to conduct an audience analysis and the second post discussed how to define the overall scope of the manual. Once the overall scope of the user guide is defined, the next step is to coordinate the team that will work on creating the manual. A typical team will consist of the following roles. Many of these roles will be fulfilled by freelancers since they are one-off or intermittent work engagements. At the end of the article, I have provided a list of websites where you can find good freelancers. Creative Artist You'll need to work with a creative artist to design the cover page and any other images for the user guide. Most small to mid-sized companies don't have a dedicated creative artist on their rolls. But that's not a problem. There are several freelancing websites where you can work with great creative ar