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

My HSQLDB schema inspection story

This is a simple story of my need to inspect the schema of an HSQLDB database for a participar FOREIGN KEY, and the interesting things I had to do to actually inspect it. I am using an HSQLDB 1.8 database in one of my web applications. The application has been developed using the Play framework , which by default uses JPA and Hibernate . A few days back, I wanted to inspect the schema which Hibernate had created for one of my model objects. I started the HSQLDB database on my local machine, and then started the database manager with the following command java -cp ./hsqldb- org.hsqldb.util.DatabaseManagerSwing When I tried the view the schema of my table, it showed me the columns and column types on that table, but it did not show me columns were FOREIGN KEYs. Image 1: Table schema as shown by HSQLDB's database manager I decided to search on StackOverflow and find out how I could view the full schema of the table in question. I got a few hints, and they all pointed to

Fuctional Programming Principles in Scala - Getting Started

Sometime back I registered for the Functional Programming Principles in Scala , on Coursera. I have been meaning to learn Scala from a while, but have been putting it on the back burner because of other commitments. But  when I saw this course being offered by Martin Odersky, on Coursera , I just had to enroll in it. This course is a 7 week course. I will blog my learning experience and notes here for the next seven weeks (well actually six, since the course started on Sept 18th). The first step was to install the required tools: JDK - Since this is my work machine, I already have a couple of JDK's installed SBT - SBT is the Scala Build Tool. Even though I have not looked into it in detail, it seems like a replacement for Maven. I am sure we will use it for several things, however upto now I only know about two uses for it - to submit assignments (which must be a feature added by the course team), and to start the Scala console. Installed sbt from here , and added the path

Inheritance vs. composition depending on how much is same and how much differs

I am reading the excellent Django book right now. In the 4th chapter on Django templates , there is an example of includes and inheritance in Django templates. Without going into details about Django templates, the include is very similar to composition where we can include the text of another template for evaluation. Inheritance in Django templates works in a way similar to object inheritance. Django templates can specify certain blocks which can be redefined in subtemplates. The subtemplates use the rest of the parent template as is. Now we have all learned that inheritance is used when we have a is-a relationship between classes, and composition is used when we have a contains-a relationship. This is absolutely right, but while reading about Django templates, I just realized another pattern in these relationships. This is really simple and perhaps many of you may have already have had this insight... We use inheritance when we want to allow reuse of the bulk of one object in other