How to have limited ZMQ (ZeroMQ - PyZMQ) queue buffer size in python?

Question

I'm using pyzmq library with pub/sub pattern. I have some fast ZMQ publishers using .connect() method and a slower ZMQ subscriber using .bind() method. Then after a few minutes, my subscriber receives the old data published from the publisher — due to ZMQ buffer.

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My Question:

Is there any approach to manage ZMQ queue buffer size? (set a limited buffer)

[NOTE]:

• I don't want to use ZMQ PUSH/PULL.
• I've read this post, but this approach clear buffer only: clear ZMQ buffer
• I also tried with high watermark options, but it didn't work:

socket.setsockopt(zmq.RCVHWM, 10)  # not working
socket.setsockopt(zmq.SNDHWM, 10)  # not working

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Publisher:

import zmq
import time

port = "5556"
context = zmq.Context()
socket = context.socket(zmq.PUB)
socket.bind("tcp://*:%s" % port)
socket.setsockopt(zmq.SNDHWM, 10)  # not working

while True:
    data = time.time()
    print("%d" % data)
    socket.send("%d" % data)
    time.sleep(1)

Subscriber:

import zmq
import time

port = "5556"
context = zmq.Context()
socket = context.socket(zmq.SUB)
socket.connect("tcp://localhost:%s" % port)
socket.setsockopt(zmq.SUBSCRIBE, '')
socket.setsockopt(zmq.RCVHWM, 10)  # not working

while 1:
    time.sleep(2)  # A speed reducer like.
    data = socket.recv()
    print(data)

The queue size is still more than 10 despite these options (via configured send/receive high watermark).

Answer 1

I found an approach to get the last message only in ZMQ subscriber using CONFLATE option.

Note that you should set the CONFLATE option before you connect:

import zmq
import time

port = "5556"
context = zmq.Context()
socket = context.socket(zmq.SUB)

socket.setsockopt(zmq.SUBSCRIBE, '')
socket.setsockopt(zmq.CONFLATE, 1)  # last msg only.
socket.connect("tcp://localhost:%s" % port)  # must be placed after above options.

while 1:
    time.sleep(2)  # Dummy delay
    data = socket.recv()
    print(data)

In other words, it removes any buffered queue on the subscriber side.

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[NOTE]:

In addition, by using zmq.SNDBUF and zmq.RCVBUF options we can set a limit on ZMQ buffer size. (More information)

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Answer 2

To set the queue/buffer size you need to set the high water marks via the socket options

setsockopt(zmq.SNDHWM, 10)
setsockopt(zmq.RCVHWM, 10)