- History must be enabled on the Edge via Transmission side configuration settings.
- A History Store must be defined under MQTT Transmission -> History -> History Stores and it must be enabled.
- A Transmitter under MQTT Transmission -> Settings -> Transmitters must consume the enabled History Store.
- Ignition 8 Only: “Enable History Storage by Default” needs to be enabled or the 'CL Store Forward EnabledStoreAndForward' custom property must exist on the Edge side Tag in order for historical events to be sent to MQTT Engine.
- History *must* be enabled on the MQTT Engine Tag and the history settings for that Tag must be as follows:
- History Enabled: true
- Storage Provider: Must be set to an existing Storage Provider
- Sample Mode: On Change
- Min Time Between Samples: 0 ms
- Ignition 7 Only: “Timestamp Source” must be set to “Value” (*not* “System”)
This is required in order for the historical event to have the timestamp when the value changed on the Edge, instead of when the historical event is being processed by Engine. Having the “Timestamp Source” set to “System” will result in historical events being inserted with the wrong (later) timestamp.
NOTE: the above history settings will ensure the proper historical event processing by MQTT Engine when writing history directly to the database and when writing history directly to the Tag.