Java Technology

Java Tuning and Trouble Shooting

            <h2>Useful JVM Settings</h2>

-Xmx512m (maximum Heap space) -Xms1024m (minimum Heap size)
starting points 2G 32 bit 3-4G 64 bit and 1:3 young vs old

Java Trouble Shooting Tools

  • heap dump
    • jmap -dump:file=filename.bin [pid]
      • hprof binary format
      • needs to be analysed in another took like MAT
      • or jhat to see in a web browser on port 7000 on local host
        • jhat -J-mx2000m filename.bin
    • jmap -histo [pid]
      • histogram of java object heap
      • quick text output
    • jmap -heap [pid]
      • to print java heap summary
  • thread dump / thread stack
    • jstack [pid]
  • enabling gc logs
    • -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -Xloggc:[logname]
  • visualJVM
  • jconsole
  • list open files for process
    • sudo lsof -p [pid]
  • list max open file limit
    • ulimit -S -n