Jit Compiler

  • How to find which methods are being compiled to native byte code by compiler.

    • By running the class with flag *PrintCompilation * turned on.-XX:+PrintCompilation

  • There are two level of compiler in java C1 and C2

    • On the basis of number of times a code block is used, it keeps on getting compiled at a more deeper tier.
    • The first three level of compilation are done by C1 Compiler
    • The C2 Compiler, compiles the code to native byte code as well places the code in code cache, hence even faster code execution. The Native level 4 compilation.
    • This whole process is termed as code profiling.
    • To view detailed logs on compilation of a class, two flags are used.
      • first to unloc the diagnostic options of VM - -XX+UnlockDiagnosticVMOptions,
      • followed by -XX:+LogCompilation to output compilation log to a file in xml format.

  • Code Cache Tuning

    • -XX:+PrintCodeCache to print existing code cache sizes
    • -XX:+ReservedCodeCacheSize=28m to set maximum code cache size
    • jconsole is used to monitor jvm