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    The nature of a commenting system is that it is IO bound […]

    […] rapidly ran out of CPU on flask machines because they were doing redundant work.

    Which is it? Because if you’re CPU bound (and at an average of 7.7 comments per second you most likely are during peaks) it makes no sense to use Python, let alone Django anywhere in your pipeline.

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      “Realtime” used to have a specific, technical meaning. It seems these days it means a responsive web app?

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        I think that many groups (my own included, somewhat guiltily) have begun using the term “realtime” to describe apps with QoS guarantees (or at least some effort to improve it).

        The classic manifestation of this problem is that if you’re doing a lot of IO in your requests, and you have a fixed threadpool handling the requests, your throughput might be limited by the size of your threadpool instead of your machine’s real characteristics, since

        throughput <= (# request workers) / (latency per request)
        

        To be fair, given the rarity of hard-realtime systems, the continuum of soft-realtime to “it feels fine” responsiveness makes it tougher to pin down what soft-realtime means.