Well, if you're getting into that, you're far enough down into the rabbit hole of optimization that you probably have a reason for being there and some business

Well, if you're getting into that, you're far enough down into the rabbit hole of optimization that you probably have a reason for being there and some business specific logic that would drive some of your specific tunings.. I'd generally recommend a selector identifying sockets that are ok for write and then delegating to a caching thread pool to handle actual transferTos. If that select loop becomes your bottleneck, you can of course horizontally scale that and have a set of selectors, striping the register()s across them to get less lock contention and having them all feed into the caching threadpool.