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There are however some caveats regarding tag history configuration persistence and handling of historical event data that are detailed in this document.

History Configuration Persistence  

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Normally if a tag is updated with a value that is older than the current value, Ignition simply throws it away. In doing so, no tag change event will ever fire and the tag will not be updated. The back-fill option allows the value to be stored to the historical database if history is enabled on that tag. However even with this option enabled, it is important to note that no tag change event will fire. So, tag change event scripts, transaction groups, and any other subsystem that relies on tag change events will not be notified of the event if it is older than the current tag value (i.e. is historical).

To enable this option, browse to the Ignition Gateway Web UI → Config → Tag Providers → Realtime. Select 'edit' for the Tag Provider that will contain Reference Tags that will point to MQTT Engine tags. Scroll to the bottom and click the 'Show advanced properties' checkbox. This will show the 'Allow Back-fill Data' option. Set it to true as shown below and then click 'Save Changes'.

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