title: Number of processor core vs the size of a thread pool
body: <p>Many times I've heard that it is better to maintain the number of threads in a thread pool below the number of cores in that system. Having twice or more threads than the number of cores is not only a waste, but also could cause performance degradation.</p>
  
  <p>Are those true? If not, what are the fundamental principles that debunk those claims (specifically relating to java)?</p>