A Java application sometimes raises an out-of-memory exception. This is usually because it has exhausted the Java heap. However, a Java application can raise an out-of-memory exception when it exhausts the memory used by Java that is not in the Java heap. We call this area non-Java memory. For example, an out-of-memory exception in the non-Java memory can happen when the JVM attempts to load too many classes. Although it is relatively rare to exhaust the non-Java memory compared to exhausting the Java heap, a Java application can consume a considerable amount of non-Java memory. This paper presents a quantitative analysis of non-Java memory. To the best of our knowledge, this is the first in-depth analysis of the non-Java memory. To do this we created a tool called Memory Analyzer for Redundant, Unused, and String Areas (MARUSA), which gathers memory statistics from both the OS and the Java virtual machine, breaking down and visualizing the non-Java memory usage. We studied the use of non-Java memory for a wide range of Java applications, including the DaCapo benchmarks and Apache DayTrader. Our study is based on the IBM J9 Java Virtual Machine for Linux. Although some of our results may be specific to this combination, we believe that most of our observations are applicable to other platforms as well.
