The Principles of Java Application Performance Tuning

• To fully tune a Java application you need at least a basic level of understanding of: Hardware; OS processes; The JVM; Garbage collection; JIT compilation; Locks; Concurrency; Class loading; Object creation.
• One procedure for Java performance tuning is to repeatedly: Specify target performance; Specify the JVM configuration(s); Check that OS CPU, memory, and IO are acceptable, or tune; Check that response times are acceptable, or tune; Check that throughput is acceptable, or tune; After any change from tuning, start again from the beginning of this sequence.
• Throughput and response times often impact each other, tuning to optimize one frequently adversely affects the other, so you need to balance to get the overall best performance.
• Currently (around when 1.7.0_51 JVM is current), the concurrent collector is the best collector for low pause times in Oracle JVMs.
• Set the New area (young generation) size sufficiently large to hold all short-lived objects, so that they are collected before they get promoted to the old generation. But too large a New area size can cause longer pauses from copying live objects, so try to avoid oversizing this.
• Recommended JVM options for a webserver: -server -Xms -Xmx -XX:NewRatio: or -XX:NewSize= -XX:MaxNewSize= -XX:PermSize=256m -XX:MaxPermSize=256m -Xloggc: -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+UseParNewGC -XX:+CMSParallelRemarkEnabled -XX:+UseConcMarkSweepGC -XX:CMSInitiatingOccupancyFraction= -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath= -XX:OnOutOfMemoryError= (stop or restart).
• If stop-the-world GC times are too long, tune the GC and use a profiler and/or heap dump to identify objects that can be eliminated.
• If CPU usage is low, analyse the concurrency behaviour using thread profilers or stack dumps to reduce wait times.
• If CPU usage is high, use a profiler to determine the execution bottlenecks and improve the algorithms.
• A tuning approach: first decide if tuning is even necessary; focus on the biggest bottleneck; much tuning is a balancing exercise so bear in mind that if you are improving one thing, you are probably making something else worse.