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100ms fixed timeout when QoS=2 (bad performances) [message #1782340]

Thu, 22 February 2018 02:02

Eclipse User

Hi,
in my project I need to publish messages with high frequency. The publish result must be synchronous, to retry the publish later in case of issues.
For this reason I am using the parameters QoS=2 and Reliable=true (message queue size equal to 1).

With this configuration Paho sends messages with a frequency of 10 messages/second (see attached wiresharkSnapshot.png). The issue seems to be related to the "timeout" const in MQTTClient_yield(), called by MQTTClient_publish function.
I tried to reduce the value to 10ms and the delay disappear, apparently without introducing drawbacks.

Do you have any suggestion about how to avoid the issue and if we can set the value to 10ms without side effects?

For reproducibility, I attached the code snippet which cause the issue.

Thanks,
Lorenzo

Attachment: wiresharkSanpshot.png
(Size: 37.87KB, Downloaded 167 times)
Attachment: paho_producer.c
(Size: 1.54KB, Downloaded 168 times)

Re: 100ms fixed timeout when QoS=2 (bad performances) [message #1790094 is a reply to message #1782340]

Mon, 04 June 2018 15:38

Eclipse User

I too am having this problem (throughput for qos=2 is only 10 packets per second). Were you able to resolve this problem? How?
Thanks,
Michael

Re: 100ms fixed timeout when QoS=2 (bad performances) [message #1790440 is a reply to message #1790094]

Mon, 11 June 2018 03:05

Eclipse User

Hi,

from what I understood from the support, this timeout regulates how long the system should wait for new messages before sending them. The purpose is to try to create a package with multiple messages to maximize the throughput.
Unfortunately for my requirement I need to send the messages one by one. So the only solution is to reduce the timeout from 100 ms to 10 ms.
I also opened a Github request and they will put this value as configurable: https://github.com/eclipse/paho.mqtt.c/issues/452

Regards,
Lorenzo

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