In realtime applications we need information from our servers as soon as it’s available – and, fundamentally, the classic HTTP request/response paradigm isn’t up to the job. The server will be silent, new data or not, unless or until a consumer requests an update. That limitation saw the emergence of all manner of hacks and workarounds as devs sought to adapt that request/responsual model to a more dynamic, realtime web. These approaches actually work quite well in specific use cases, Gmail chat for instance. Problems emerge in low-latency applications or at scale, mainly because of the processing demands associated with HTTP.
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