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AWS IoT has a message size limit of 128KB. As a result, messages published from MQTT Transmission or MQTT Engine that exceed that limit can cause connection to the broker to oscillate.

MQTT Sparkplug BIRTH and DEATH message lengths

As required by the Sparkplug Specification data is published on the are the NBIRTH, NDEATH, DBIRTH and DDEATH topics.

The payloads for each of these messages include every metric the device will ever report on. At a minimum these metrics must include the name, datatype and current value.

If you have large number of tags in a single folder, these messages can easily exceed the 128KB limit.

Resolution

  • Distribute the tags into multiple device folders such that each NBIRTH, NDEATH, DBIRTH or DDEATH message is less than 128KB
  • Check that your Tag Pacing period is not causing messages greater the 128KB to be generated. Tag pacing is the buffer period for outgoing Transmission messages which allows tag change events to be buffered to reduce the number of generated MQTT messages.



Unable to Resolve?

If the troubleshooting tips did not help you resolve your issues, please open a ticket with Support making sure to include the MQTT Engine or MQTT Transmission logs as appropriate.  

From the Ignition Logs view, select the Download icon to download a copy of the system-name.idb file to your local file system. You will need to compress (zip, 7z or rar) this file before sending to Support.



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