Michael A. Jackson. Principles of Program Design, Academic Press, 1975

We follow two rules in the matter of optimization:

Measure!

Profiler

• instrument all of the methods
  
• methods "report" whenever they are run
  
• bytecode of your classes is changed
  
• crashed large apps
  

Sampler

• lots of thread dumps
• analyze stack traces
• faster
• does not require changes

Workshop

https://github.com/lingaro/java-performance-workshop

http://bit.do/jperf

Compare!

Java
Microbenchmark
Harness

• Hard to do reliably
• Tiered Compilation: C1 - client, C2 server compiler
  • Level 0 –interpreted code
  • Level 1 – simple C1 compiled code (with no profiling)
  • Level 2 – limited C1 compiled code (with light profiling)
  • Level 3 – full C1 compiled code (with full profiling)
  • Level 4 – C2 compiled code (uses profile data from the previous steps)
• Dynamic recompilation