CODEWITHSUNDEEP
mqtt
Stan Huang at Taiwan
Stan Huang at Taiwan

Reputation: 529

Why does MQTT acknowledge so slow?

I wrote an MQTT client program, which runs at a computer (computer 1). The MQTT client program connects to an MQTT Broker with QoS=1 and publishes data to Broker periodically. I subscribe the Broker (Qos=1) from another computer (computer 2), using Mosquito utility. I found the data published to Broker will be delay delivered to publisher about 3 seconds. The delayed time is too long. I checked the codes and found the 3-second-delay time is from read_packet() which is to read back acknowledge from Broker. Why is there such long delay time? How can I figure it out? The Broker (MQTT server) is managed by my coworker. If the Broker is the cause, I can request them to help. But I need to know what could be the trouble source, so that I can check with them.

I can confirm the delay occurring at the time of reading back acknowledge from Broker by watching the debugging message from MQTT client program at computer 1. For Qos = 1, the client must read back acknowledge after sending (publishing) packets. I found 3-second delay time between sending packet and reading back acknowledge. Surely, I also found the delay at display of Mosquito_sub utility.

Upvotes: 1

Views: 4671

Answers (1)

hardillb
hardillb

Reputation: 59866

Assuming near instant network comms and nothing else strange going on the fact that you have recreated the problem with mosquitto_sub then this points to the MQTT broker being the source of the problem.

Without knowing what broker you are using and how heavily it is loaded it's hard to say more but you should look at the broker logs.

Upvotes: 2

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