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Java Profilers

JVM generates a lot of events in either of the categories below:

  • Instant events - one time events that have a timestamp and event data. Example: Exception events, Class load events, Object allocation events.
  • Duration events - provide start time and end time of an activity. Example: Garbage collection, monitor wait, monitor contended.

JVM also has profiling functions to provide data on JVM internal state. Example: getThreadState(), getAllThreads(), getStackTrace() and getAllStackTraces(). All these functions are called requestable events by Java Flight Recorder.

Java profilers monitor JVM execution at the bytecode level. They can:

  • Passively listen to JVM events
  • Actively query JVM stats
  • Modify bytecode

Profiling activities

  • CPU profiling - finds what methods run the most frequently and use the most CPU time. Such methods are called Hot methods. This information can be retrieved either by sampling or instrumentation.
  • Memory profiling - concerned with understanding what objects are using up memory and how memory is freed.
  • Thread profiling - concerned with what states threads are in and why.
  • I/O profiling

Profiling Metrics

Java profilers provide information on:

  • thread execution and locks
  • heap memory usage
  • garbage collection
  • hot methods
  • exceptions
  • class loading
  • etc.

Tools

  • JProfiler
  • Yourkit Java Profiler
  • Java VisualVM
  • Netbeans Profiler
  • Java Flight Recorder
  • Application Performance Management products
Last update: February 16, 2023