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To enable history configuration is required at MQTT Engine, at each MQTT tag, and at the MQTT Transmission module. In addition, a History Store must also be defined for MQTT Transmission.
See the Ignition documentation Configuring Tag History for additional help.
There are two ways that MQTT Engine historical event processing can insert historical data into Ignition’s Tag Historian Module:
The configuration parameters required to write historical events directly to the database, via the Historian, bypassing the Tag are detailed below.
Under the MQTT Engine Settings General Tab, navigate to the Miscellaneous Settings and ensure Store Historical events is selected
Under the MQTT Transmission Settings for your transmitter, navigate to the History Settings and ensure that In-Order History is de-selected.
There are several reasons why you might need to write directly to the tag which include:
The configuration parameters required to write historical events to the Tag instead of directly to the Historian are detailed below.
Under the MQTT Engine Settings General Tab, navigate to the Miscellaneous Settings and ensure Store Historical events is de-selected
Under the MQTT Transmission Settings for your transmitter, navigate to the History Settings and ensure that In-Order History is selected. This ensures that when the Edge side client comes back online and flushes history, it will flush the oldest historical events first (in order) before sending live Tag changes events to Engine.
However, deleting MQTT Engine tags can be required in certain cases. One example is if UDTs are being propagated from the Edge and the UDT definition on the Edge has been updated. This requires one to delete all instances of the UDT under MQTT Engine and delete the corresponding UDT definition so that it can be recreated/updated at MQTT Engine for the Edge side changes to take affect.
There are two options for persisting history configuration in this case and they are as follows:
Configuring history on tags indirectly referencing MQTT Engine tags will work properly if the referencing tag is a Reference tag only. Derived, Expression and OPC tags (expose MQTT Engine tag provider through OPCUA server) will not properly store history when MQTT Engine tags are updated with historical data at a high rate of speed. This is a limitation within the Ignition platform and may be addressed in a future release.
One can determine the current size of the History Store by examining the History Store metric tags under [MQTT Transmission]Transmission Info/History Store. These tags will show the number of historical metrics stored per edgenode/device and how much memory/disk is being consumed by these metrics. These tags update live (count down) as historical data is flushed.
Review Determining the settings for an MQTT Transmission History Store for help in determining the correct configuration for your History Store
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