http://javad.dev/tags/performance/Recent content in Performance on Javad Rajabzadeh | Senior Software EngineerHugoen-usSat, 19 Sep 2026 15:30:00 +0330http://javad.dev/posts/hydra-range-preemption-engine/Sat, 19 Sep 2026 15:30:00 +0330http://javad.dev/posts/hydra-range-preemption-engine/<p>Every download manager ever shipped asks its user two questions before a single byte has moved: how many connections should I open, and how finely should I slice the file? Both are scheduling decisions made with zero observations in hand, and both have unbounded worst-case error. Split an object evenly across $N$ connections and the makespan ratio against the achievable optimum is $\overline{\gamma}/\gamma_{\min}$ — unbounded in how heterogeneous the connections turn out to be. Split it in proportion to measured rates instead, which is the obvious repair, and it is <em>also</em> unbounded, because any division fixed at $t=0$ is wrong the moment one rate moves.</p>