Do zmq subscribers know to skip subsequent parts of filtered topics for multipart messages?

Question

Say I have a publisher_socket and a subscriber_socket, created in two different processes. The publisher_socket publishes a two-part message, outlined in pseudo-code below.

publisher_socket.send("huge_blob", ZMQ_SNDMORE)
publisher_socket.send([ 1GB buffer of data ])

Suppose thesubscriber_socket is not set up its message filter to subscribe to the topic "huge_blob". Does the associated background thread know to skip ingestion of the second part of the message? Or might I see the subscriber's memory usage shoot up to 1GB as the background thread copies the second part of the message from the network, even though it will never be used?

Answer 1

from zeromq v3 onwards all subscriptions are filtered on the publisher side. When you subscribe on your ZMQ_SUB socket, the filter information is sent to the ZMQ_PUB socket and filtered there.

So the answer is no, you ZMQ_SUB process, socket, network etc will not see the first or second frame if they are not subscribed to "huge_blob"