[zeromq-dev] Why ZMQ drop messages?

Emmanuel TAUREL taurel at esrf.fr
Wed Nov 23 17:16:11 CET 2011


Hello all,

I am using ZMQ 3.0.x on linux boxes with  the PUB/SUB pattern.
I have only one subscriber which is very slow. It needs 1 second every 
time a message is read.
I have a HWM on the publisher side set to 10.

In my message, I have a counter which is incremented for each message.
My messages are relatively small (150 bytes)
I have a print of date each time the publisher sends a message 
(gettimeofday)
I also have on the same host where the publisher is running a wireshark 
tool which captures network packets.

With wireshark, I see that ZMQ drops messages number 11 to 39. I don't 
understand why.
All the previous messages (number 1 to 10) have been sent on the network 
because I see them on wireshark
The time reported by wireshark is coherent with the time printed by the 
publisher.

Message 8 sent by publisher at xxx623,205547
Message 8 seen by wireshark at xxx623,205556

Message 9 sent by publisher at xxx623,205575
Message 9 seen by wireshark at xxx623,205584

Message 10 sent by publisher at xxx623,205603
Message 10 seen by wireshark at xxx623,205611

Message 11 sent by publisher at xxx623,205629
Message 12 sent by publisher at xxx623,205654
Message 13 sent by publisher at xxx623,205704
Message 14 sent by publisher at xxx623,205729
....

These messages are not seen by wireshark because I guess ZMQ took the 
decision to drop them.
But why it took that decision? I don't think there are messages in the 
queue because I have seen them on
the wire!

Is there something I have missed?
Any explanations are welcome

Thank's in advance

Emmanuel





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