debugging_and_profiling

Debugger

• When a breakpoint is hit, the debugger automatically suspends all threads of the process.

Reactive Tools

• info about performance issues that have happened
• example:
  • thread dump analyzer
  • jcmd
  • jstack
  • JFR

Proactive tools

• info about problems about to start or already in progress
• realtime monitoring of latency+throughput
• alerting capability
• example:
  • Pinpoint (used for tracing)
  • Datadog
  • Prometheus
  • New Relic
  • Java Mission Control (JMC)
  • jvisualvm

Java Mission Control

• GUI tool (to be downloaded separately after JDK 11)
• Click MBean Server > Threads to see live threads

Java Flight Recording

• Very lightweight and very detailed analysis
• Can be done via Java Mission Control
• Click Flight Recorder and start the recording
• To save the recording right click and dump the data

Java Microbenchmark Harness (JMH)

• provided in JDK 12 or above
• Helps perform microbenchmarking (specific parts of the program)
• library to help benchmark performance and throughput (recording time/speed/number of operations/etc.) different parts of the program
• Annotations can be used at class as well as method level

Memory leaks

• objects are unintentionally retained in memory and not released for garbage collection
• symptoms:
  • increase memory usage over time
  • out of memory errors
  • unresponsive and crashing
  • growing heap size
• diagnosis:
  • analyze heap dumps
  • use memory profilers
  • monitor memory usage
• take a memory snapshot
• tools for heap dump:
  • jmap
  • jcmd
• tools for memory profiling:
  • visualvm
  • your kit
  • eclipse MAT

CPU profiling

• CPU usage
• Method hotspots
• Thread CPU usage
• Method Call tree