Heisenprofiling, verb: wasting unnecessary time trying to figure out why your inner loops are still running slowly after optimization, only to realize that it's because the profiler hooks are slowing it down...
Oh, totally. (Although this particular operation is sometimes being hit tens of thousands of times per page load, so it was worth the attention.)
Problem was, I didn't *realize* it was down to a microsecond (and indeed, the higher-level function I actually cared about was down to five microseconds), until I realized that I was now mostly measuring residual noise from the profiler. I had actually achieved an 80% speedup, but *thought* I'd only achieved 20%, because of over-measurement, and was confused by the lack of progress.
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Problem was, I didn't *realize* it was down to a microsecond (and indeed, the higher-level function I actually cared about was down to five microseconds), until I realized that I was now mostly measuring residual noise from the profiler. I had actually achieved an 80% speedup, but *thought* I'd only achieved 20%, because of over-measurement, and was confused by the lack of progress.
Hence, Heisenprofiling...