[Solved] Consider this Python code snippet using Paho MQTT client: client.publish('sensor/data', 'temp=22', qos=0) client.publish('sensor/data', 'temp=23', qos=1) client.... | Raspberry Pi

Raspberry Pi - MQTT for IoT

Consider this Python code snippet using Paho MQTT client:

client.publish('sensor/data', 'temp=22', qos=0)
client.publish('sensor/data', 'temp=23', qos=1)
client.publish('sensor/data', 'temp=24', qos=2)

What is the expected behavior regarding message delivery?

AAll messages are delivered exactly once

BFirst message may be lost, second delivered at least once, third exactly once

CAll messages may be lost without retry

DFirst message delivered at least once, others may be duplicated

Step-by-Step Solution

Solution:

Step 1: Analyze QoS 0 message delivery
QoS 0 means message sent once, no retry, may be lost.
Step 2: Analyze QoS 1 and QoS 2 messages
QoS 1 guarantees at least once delivery (may duplicate), QoS 2 guarantees exactly once delivery.
Final Answer:
First message may be lost, second delivered at least once, third exactly once -> Option B
Quick Check:
QoS 0=may lose, QoS 1=at least once, QoS 2=exactly once [OK]

Quick Trick: Remember QoS 0 no retry, QoS 1 retry, QoS 2 handshake [OK]

Common Mistakes:

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Consider this Python code snippet using Paho MQTT client: