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News: Common benchmarking errors you will want to avoid

  1. Every once in awhile each and every one of us is trying to measure performance of certain parts of the code. It can be either a fully functional application measured against specific number of user transactions per minute or a microbenchmark. Which you have written to prove that your fellow developer is wrong. Especially in the latter case it is beneficial to be aware of the pitfalls skewing your benchmark results:

    1. Noisy neighbours. Running on a desktop? Are you sure you have switched off the torrent client? Or what about the windows updates? Or disk defrag? Running on a server? Are you virtualized? Are you sure the other  instances in the same hardware do not do something which is tough to virtualize properly - such as intense I/O?
    2. Garbage collection pauses. Do you now the pause times introduced during the test? Sure they haven't tampered your results?
    3. JIT optimizations. Are you running your measurements on optimized or unoptimized code? How do you know?
    4. Class loading. Are all the classes loaded and initialized before the measurement starts? Or do you suffer from the lazy loading consequences?
    5. Different architecture. Are you running on the same platform used in production? Same number of cores? Same 64bit architecture? Are you sure?
    6. Measurements. Are your measurements in nanoseconds? Sure you are not in the wrong territory? Maybe you still can to create a more coarsely grained test and reach into safer "seconds and tens of seconds" territory instead of the nano-level?

    All in all - if this frightened you off from writing your next microbenchmark then - good. Because most often you shouldnt. But if you still are into it, you can check out the more detailed post on the subject from this blog.

    Threaded Messages (1)

  2. Anti-virus.. caching[ Go to top ]

    Don't forget the dreaded anti-virus.

    Also - caching impact if running with the same queries - only need a cache of size 1 if you're using the 1 search input.