[DeveloperWorks] Garbage collection in WebSphere Application Server V8, Part 1: Generational as the new default policy

Garbage collection in WebSphere Application Server V8, Part 1: Generational as the new default policy

Introduction

Garbage collection (GC) is an integral part of the Java Virtual Machine (JVM) as it collects unused Java heap memory so that the application can continue allocating new objects. The effectiveness and performance of the GC play an important role in application performance and determinism. The IBM JVM provided with IBM WebSphere Application Server V8 (on supported platforms) provides four different GC policy algorithms:

• -Xgcpolicy:optthruput
• -Xgcpolicy:optavgpause
• -Xgcpolicy:gencon
• -Xgcpolicy:balanced

Each of these algorithms provides different performance and deterministic qualities. In addition, the default policy in WebSphere Application Server V8 has changed from -Xgcpolicy:optthruput to the -Xgcpolicy:gencon policy. Let’s take a look at each of these policies and see what this change in the default policy means.