Tuning the Java Virtual Machine for Stability and Speed

Abstract: Memory management in the Sun Java Virtual Machine (JVM) can be hard to understand. Garbage Collection (GC), the process of cleaning-up memory after use, can have dramatic and fatal effects on application performance. Garbage Collection stop-the-World events are the primary limiting factor in sizing the JVM for large institutions. With over 50,000 active users in courses as large as 1200 students, and having over 7000 active courses, the University of Toronto encountered some very unusual problems when sizing the JVM heap on Sun T2000 hardware with 32GB of 64-bit memory. Working closely with Sun Microsystems, a detailed analysis of JVM GC performance identified three issues that could not be replicated in a test environment and had to be debugged on the live systems, all the while providing continuous service to users. Careful tuning and the creation by Sun of a new command-line option for the JVM were required to resolve the issues.