Understanding memory usage in your Java application with Amazon CodeGuru Profiler

“Where has all that free memory gone?” This is the question we ask ourselves every time our application emits that dreaded OutOfMemoryError just before it crashes. Amazon CodeGuru Profiler can help you find the answer.

Thanks to its brand-new memory profiling capabilities, troubleshooting and resolving memory issues in Java applications (or almost anything that runs on the JVM) is much easier. AWS launched the CodeGuru Profiler Heap Summary feature at re:Invent 2020. This is the first step in helping us, developers, understand what our software is doing with all that memory it uses.

The Heap Summary view shows a list of Java classes and data types present in the Java Virtual Machine heap, alongside the amount of memory they’re retaining and the number of instances they represent. The following screenshot shows an example of this view.

Figure: Amazon CodeGuru Profiler Heap Summary feature

Because CodeGuru Profiler is a low-overhead, production profiling service designed to be always on, it can capture and represent how memory utilization varies over time, providing helpful visual hints about the object types and the data types that exhibit a growing trend in memory consumption.

In the preceding screenshot, we can see that several lines on the graph are trending upwards:

• The red top line, horizontal and flat, shows how much memory has been reserved as heap space in the JVM. In this case, we see a heap size of 512 MB, which can usually be configured in the JVM with command line parameters like -Xmx.
• The second line from the top, blue, represents the total memory in use in the heap, independent of their type.
• The third, fourth, and fifth lines show how much memory space each specific type has been using historically in the heap. We can easily spot that java.util.LinkedHashMap$Entry and java.lang.UUID display growing trends, whereas byte[] has a flat line and seems stable in memory usage.

Types that exhibit constantly growing trend of memory utilization with time deserve a closer look. Profiler helps you focus your attention on these cases. Associating the information presented by the Profiler with your own knowledge of your application and code base, you can evaluate whether the amount of memory being used for a specific data type can be considered normal, or if it might be a memory leak – the unintentional holding of memory by an application due to the failure in freeing-up unused objects. In our example above, java.util.LinkedHashMap$Entry and java.lang.UUIDare good candidates for investigation.

To make this functionality available to customers, CodeGuru Profiler uses the power of Java Flight Recorder (JFR), which is now openly available with Java 8 (since OpenJDK release 262) and above. The Amazon CodeGuru Profiler agent for Java, which already does an awesome job capturing data about CPU utilization, has been extended to periodically collect memory retention metrics from JFR and submit them for processing and visualization via Amazon CodeGuru Profiler. Thanks to its high stability and low overhead, the Profiler agent can be safely deployed to services in production, because it is exactly there, under real workloads, that really interesting memory issues are most likely to show up.

Summary

For more information about CodeGuru Profiler and other AI-powered services in the Amazon CodeGuru family, see Amazon CodeGuru. If you haven’t tried the CodeGuru Profiler yet, start your 90-day free trial right now and understand why continuous profiling is becoming a must-have in every production environment. For Amazon CodeGuru customers who are already enjoying the benefits of always-on profiling, this new feature is available at no extra cost. Just update your Profiler agent to version 1.1.0 or newer, and enable Heap Summary in your agent configuration.

Happy profiling!