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History must be enabled on the tag (either directly on the MQTT Engine tag or reference tag) but the only property used from the tag history configuration is the Storage Provider.

All historic data will be written to the configured Storage Provider, via the Historian, using the timestamp associated with the historical data.

Note
All other properties such as Sample Mode, Max Time Between Samples, Deadband etc are ignored when writing historic data

History Configuration Examples

Sample Mode = On Change, Min Time Between Samples = 0, Max Time Between Samples = 0

  • Real-time data is written to the storage provider on each tag change event whilst the tag quality is Good
  • Historical data is written to the storage provider using the timestamp associated with the historical data 
    • Handles historical metrics flushed from the Edge that have very high resolution; e.g., the historical metrics have timestamps 1 ms apart for a single tag

Sample Mode = On Change, Min Time Between Samples = 0, Max Time Between Samples = 5

  • Real-time data is written to the storage provider on each tag change event whilst the tag quality is Good
  • Real-time data is written to the storage provider on the Max Time Between Samples interval if no tag change events whilst the tag quality is Good
  • Historical data is written to the storage provider using the timestamp associated with the historical data 
    • Max Time Between Samples inserts will not be inserted into the middle of historical data
    • Handles historical metrics flushed from the Edge that have very high resolution; e.g., the historical metrics have timestamps 1 ms apart for a single tag

Sample Mode = Periodic, Max Time Between Samples = 0, Sample Rate = 5

  • Real-time data is written to the storage provider on the Sample Rate whilst the tag quality is Good
  • Historical data is written to the storage provider using the timestamp associated with the historical data



Anchor
writetotag
writetotag
Writing historical events directly to tag

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Note

If you are using MQTT Transmission as the Edge side client, 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 MQTT Transmission 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. 

Examples


Back-fill support

Historical back-fill support was added in Ignition 8.1.4 which allows Reference Tags in Ignition to be updated even if history arrives out of order. See the following document for details : MQTT History Back-Fill with Reference Tags

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