[zeromq-dev] Using zeromq in a distributed load pipeline, can I get the address of the last server a message was sent to?

[Pieter Hintjens]

John,

There are several aspects here.

- The tcp:// transport is disconnected.  You can send, and then later
a recipient can connect, and it will get the message.
- The send() function itself runs in the background and thus the
actual TCP send can happen much later even if the recipients are
already connected.  So you'd need some other API to get back the
sender address and some way to tie this to specific send() operations.
- If you're doing several million per second, that would become hugely
expensive to store and process.
- With some transports (multicast) there are no receivers.
- 0MQ hides the connected nodes unless you are doing explicit routing
with the XREP socket.  This is both for reasons of simplicity and
scalability.  E.g. a publisher that has to manage or track all its
subscribers is much less scalable than one that does not.

-Pieter

On Sat, Oct 2, 2010 at 4:13 AM, John Connor
<john.theman.connor at gmail.com> wrote:
> Thanks for the reply Joshua,
> But I still don't understand why the send function can't return the
> address that it sent the message to "because it is async".  Why should
> that have any effect on whether or not it exposes the address of the
> endpoint it sent to?  Once connected, is the address no longer stored
> in a usable form?
> I don't want to have to use req/rep just so that the receiver can tell
> the sender that it got the message and what its address is, that seems
> like way over kill.  TCP ensures that the receiver will get the
> message, and the sender already knows the address its sending to, so
> the whole req/rep thing seems redundant.  Its looking like the only
> solution is for me to maintain a list of separate sockets and iterate
> over them when sending messages so that I know what server I'm sending
> the message to.  Do you know if there would be a lot of overhead with
> creating multiple sockets instead of multiple connections?
> I appreciate your help,
> --Connor
>
> On Fri, Oct 1, 2010 at 8:26 PM,  <zeromq-dev-request at lists.zeromq.org> wrote:
>> No, ZeroMQ doesn't expose where it sends the data because it is asynchronous. If you need this information, you can possibly do it with a request/reply. The request being the msg sent to the server, the reply being the information from that specific server.
>>
>> You should also change from DOWNSTREAM/UPSTREAM to PUSH/PULL because the downstream/upstream naming is deprecated.
>>
>> Joshua
>>
>> On Oct 1, 2010, at 5:41 PM, John Connor wrote:
>>
>>> Hello,
>>> Sorry if this question is a dupe, but I'm just starting to use zeromq
>>> for a project, and I have looked everywhere for an answer to this
>>> question:
>>>
>>> If I set up a pipeline which distributes load across a cluster, I
>>> would like to log on the sender where its messages get sent. This is
>>> what I have in mind (python):
>>>
>>> import zmq
>>> context = zmq.Context()
>>> socket = context.socket(zmq.DOWNSTREAM)
>>> socket.connect("tcp://127.0.0.1:5000")
>>> socket.connect("tcp://127.0.0.1:6000")
>>>
>>> msg = "Hello World\0"
>>> connection_string = socket.send(msg)
>>> # should print "Sent message to tcp://127.0.0.1:5000"
>>> print "Sent message to", connection_string
>>>
>>> But I cant find anything that talks about this. Any help at all is appreciated.
>>>
>>> Thanks,
>>> --Connor
>>> _______________________________________________
>>> zeromq-dev mailing list
>>> zeromq-dev at lists.zeromq.org
>>> http://lists.zeromq.org/mailman/listinfo/zeromq-dev
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>



-- 
-
Pieter Hintjens
iMatix - www.imatix.com