mohanraj nagasamy

Java Performance

Notes from Java Performance by Charlie Hunt. Reference book by Charlie Hunt and Binu John.

Lesson 1: JVM Overview

  • From Java 7u21, there is server JRE available for UNIX 64 bit OSes. It has got it everything jdk has, except no browser plug-in, no auto updater.

  • Understand the major components of a modern Java Virtual Machine

    • HotSpot VM runtime
    • Garbage collector/ memory manager
      • Generational GC – it partitions the Java heap into two or more regions / generations
        • Young vs Old
      • Permanent Generation – Holds class data structures
        • In Java 8 – it has been eliminated in favor of a meta-space
    • JIT Compiler
      • Generates native byte code
      • Client mode
      • Server mode
      • Tiered – Default In Java 8 – enabled via -XX:+TieredCompilation
  • Runtime subsystem

    • -XX:+PrintFlagsFinal
    • -XX:+PrintGCDetails
  • Understand the memory management garbage collection (GC) subsystem
    • jvisualvm
      • Install plug-in visual GC
      • Install memory-pool plug-in from here
      • Once objects reaches 15 max tenuring, will promoted to old gen space
      • jTop
    • JIT compiler subsystem
      • Look at code cache from memory-pool plug-in for JIT compilation

Lesson 2: Collecting Performance Statistics

  • Understand the importance of a methodology
  • Understand which operating system metrics to monitor
    • Understand which operating system metrics to monitor: Monitor metrics on Windows. You can monitoring CPU, Memory, Network:

      1. GUI Tool: Performance Monitor
      2. CMD Tool: typeperf
    • Understand which operating system metrics to monitor: Monitor metrics on Linux

      1. GUI Tool: System Monitory in Ubuntu
      2. CMD tool: vm_stat mpstat -P ALL top
      3. Monitor the CPU Scheduler Run Queue use vmstat to monitor run queue
      4. Monitor High Voluntary Context Switching
        • Can indicate Java application that are experiencing lock contention
          • Makes it difficulties in scaling
        • Use pidstat to monitor (need sysstat package required)
          ex: pidstat -w -I -t -p <pid> <interval> Monitor network use nicstat Monitor disk/io use iostat
  • Understand what JVM metrics to monitor
    • Important JVM metrics:
    • Garbage collection: Use PrintGCDetails to log gc details you can also use -XX:+PrintGCDateStamps or -XX:+PrintGCTimeStamps – gives point and time when the gc has occurred use -Xloggc=/somepath/gc.log – to log gc log
    • Monitor app exectution time and stopped time
      • Use -XX:+PrintGCApplicationStoppedTime and -XX:+PrintApplicationConcurrentTime
    • Other to consider but not necessarily required
      • JIT compilation: -XX:+PrintCompilation, -XX:+PrintInlining – these flags are not generally used.
      • Fine tune JVM heap space sizes: -XX:+PrintTenuringDistribution, PrintAdaptiveSizePolicy (Paraller GC or G1 only)
    • Remote monitoring using jstatd
      • Requires a security manager and security policy file
    • App level metrics to monitor:
      • Begin and end time of a transaction
      • Observing app level JMX MBeans especially those that offer performance information
      • Java EE container stats:
        • Available JDBC connections
        • Active/Available Threads
        • Request arrival rate
        • Request response times
      • Build App level stats via MBeans. Example is on the book.

Lesson 3: Understand HotSpot JVM GC Logs

  • Understand how Parallel GC works
    • Understand Parallel GC logs
  • Understand how CMS GC works
    • Understand CMS GC logs
  • Understand how G1 GC works
    • Understand G1 GC logs

All of them produces totally different information

Lesson 4: Tune the HotSpot JVM Step-by-Step

  • Create a plan of attack
    • Throughput vs Latency vs Footprint
  • Understand the step-by-step process
  • Determine memory footprint size
  • Tune for latency / responsiveness: Tools to help visualize gc pause times: gchisto, censum from
  • Tune for throughput: -XX:+AggresiveOpts to turn on aggressive gc optimizations

More resources:

I would highly encourage to read the book or take the LiveLessons. Charlie Hunt is awesome!