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POZeroMQ PUB socket buffers all my out going data when it is connecting
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copied!<p>I noticed that a zeromq PUB socket will buffers all outgoing data if it is connecting, for example</p> <pre><code>import zmq import time context = zmq.Context() # create a PUB socket pub = context.socket (zmq.PUB) pub.connect("tcp://127.0.0.1:5566") # push some message before connected # they should be dropped for i in range(5): pub.send('a message should not be dropped') time.sleep(1) # create a SUB socket sub = context.socket (zmq.SUB) sub.bind("tcp://127.0.0.1:5566") sub.setsockopt(zmq.SUBSCRIBE, "") time.sleep(1) # this is the only message we should see in SUB pub.send('hi') while True: print sub.recv() </code></pre> <p>The sub binds after those messages, they should be dropped, because PUB should drop messages if no one connected to it. But instead of dropping messages, it buffers all messages.</p> <pre><code>a message should not be dropped a message should not be dropped a message should not be dropped a message should not be dropped a message should not be dropped hi </code></pre> <p>As you can see, those "a message should not be dropped" are buffered by the socket, once it gets connected, it flush them to SUB socket. If I bind at the PUB socket, and connect at the SUB socket, then it works correctly.</p> <pre><code>import zmq import time context = zmq.Context() # create a PUB socket pub = context.socket (zmq.PUB) pub.bind("tcp://127.0.0.1:5566") # push some message before connected # they should be dropped for i in range(5): pub.send('a message should not be dropped') time.sleep(1) # create a SUB socket sub = context.socket (zmq.SUB) sub.connect("tcp://127.0.0.1:5566") sub.setsockopt(zmq.SUBSCRIBE, "") time.sleep(1) # this is the only message we should see in SUB pub.send('hi') while True: print repr(sub.recv()) </code></pre> <p>And you can only see the output</p> <pre><code>'hi' </code></pre> <p>This kind of strange behavior cause a problem, it buffers all data on a connecting socket, I have two servers, server A publishes data to server B</p> <pre><code>Server A -- publish --> Server B </code></pre> <p>It works fine if server B gets online. But what if I start the Server A and do not start Server B?</p> <p>As the result, the connecting PUB socket on Server A keeps all those data, the memory usage gets higher and higher. </p> <p>Here is the problem, is this kind of behavior a bug or feature? If it is feature, where can I find a document that mentions this behavior? And how can I stop the connecting PUB socket buffers all data?</p> <p>Thanks.</p>

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