[zeromq-dev] Extremely strange PUB/SUB behavior

[Calvin de Vries]

Hi,

I'm seeing some extremely strange behavior in production with ZeroMQ. It
seems as if I stop receiving messages for a certain subscription and am not
sure why. I've been using my current pattern in production for months and
this has occurred twice in that time frame (once today and once last week)
and any time I try to reproduce it, I cannot.

Basically, I have a Linux C++ server using a PUB socket to send out
messages for many different subscriptions (about 3000 different
subscriptions each is a char* 1-5 letters long) once every 5 seconds to
Windows C++ clients using a SUB socket. It sends out a message for every
single subscription in that time frame. Any given client may be subscribed
for anywhere between 10-100 unique subscriptions. One of my clients (the
same one actually out of around 30-35) stopped receiving messages for just
one of the subscriptions. Another client that has the same subscription
list does not stop receiving any messages for any subscription. The first
time, this behavior had eventually somehow "fixed" itself, the client
started receiving messages for all subscriptions once again. Today when it
happened, the client was restarted and received all subscriptions again as
well.

Since both times another client with the same subscription had still been
receiving messages, I know that the publisher is still sending out the
message. It's not a socket becoming "closed" because it is only one socket
and still receiving messages for other subscriptions.  It seems that this
is extremely rare, though so every time I try to document with a test case,
I cannot do it. My best guesses to the cause of this problem sound
ridiculous - the subscription somehow becoming "cleaned up" or
"unsubscribed" for no reason. I just can't justify it and don't see how
that could possibly be happening.

I'm curious if anyone has ever noticed anything like this, or if there's
perhaps some sort of flaw in my system. It seems very straightforward to me
and am still baffled how this is occurring.

Any help, insight or suggestions would be greatly appreciated.

Thank you,
Calvin de Vries
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