Sizer.sizeof

What is this?

A tool to measure memory usage of Java objects at runtime by traversing the object graph and adding up the bytes for fields and objects.

Why would anyone want to use this?

• Investigate heap usage problems. Profilers are good for looking at heap-wide histograms and finding allocation hotspots, but can't easily drill down to specific objects. Also, taking a heap dump usually requires halting execution.
• Planning.
  • e.g. What's the memory overhead of caching X?
• Curiosity?

Why another Java object graph sizer?

I wanted a tool that met the following criteria:

• Accuracy
• Performance
• Clear licensing (Apache License, 2.0)
• Stability
• Hosted in a public repo
• No dependencies

How to add to your project

You can either build from scratch using mvn:

1. Clone this repo
2. mvn package
3. Add target/javasizer-VERSION.jar to your classpath

How to use

Add this to your JVM arguments:

--add-opens java.base/java.lang=ALL-UNNAMED
--add-opens java.base/java.util=ALL-UNNAMED

org.jh.Sizer.sizeof(root) will return the bytes used by the object graph.