[zeromq-dev] Behavior on HWM reached

Pieter Hintjens ph at imatix.com
Tue Jun 24 13:31:08 CEST 2014

Outgoing messages may be dropped in the ROUTER socket, however the
DEALER socket will not drop messages.

I've fixed the FAQ to be more accurate.

On Mon, Jun 23, 2014 at 2:35 PM, Diego Fons <diego.fons at intraway.com> wrote:
> Hi,
> I'm facing some problem on a DEALER/ROUTER schema (more than one client
> DEALER, one server ROUTER). I'm suspecting that some messages are being
> dropped in the DEALER socket. The client apps works with very high load (cpu
> and mem).
> Reading the FAQ [1] in ZMQ site, I read this:
> <quote>
> How does the HWM (high water mark) work with any socket type?
> It works the following way right now:
> The I/O thread reads messages from the pipe and pushes them to the network.
> If network is not able to accept more data (e.g. TCP backpressure is
> applied) it stops reading messages from the pipe and waits until the network
> is ready for accepting more data.
> In the application thread, messages are simply pushed to the pipe when
> zmq_send() is called. If the pipe is full (HWM is reached) the message is
> dropped.
> The problem with the above approach is that when you send a lot of messages
> is a quick sequence (e.g. sending small messages in a tight loop) the
> messages are stored in the pipe until it is full and the subsequent messages
> are simply dropped. The sender is not even notified about the fact that
> messages are disappearing.
> The main core developer is hopeful that some community members will
> volunteer to assist in replacing this mechanism with a rate flow control
> mechanism.
> </quote>
> So, is this behavior the one implemented in 4.0.4? Because this could be the
> reason of my problem.
> [1] http://zeromq.org/area:faq
> --
> Diego Andrés Fons
> Intraway Corp.
> Solution Developer
> AR Office: +54 (11) 6040 4000
> US Office: +1 (516) 620 3890
> Email: diego.fons at intraway.com
> Visit our website at http://www.intraway.com
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