# MQTT & Historian

**URL:** <https://forum.inductiveautomation.com/t/mqtt-historian/62695>\
**Category:** Ignition\
**Created:** [August 4, 2022, 7:07pm UTC](https://forum.inductiveautomation.com/t/mqtt-historian/62695 "2022-08-04T19:07:56Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![jykl5](https://avatars.discourse-cdn.com/v4/letter/j/9de053/32.png) [@jykl5](https://forum.inductiveautomation.com/u/jykl5)\
**Post date:** [August 4, 2022, 7:07pm UTC](https://forum.inductiveautomation.com/t/mqtt-historian/62695/1 "2022-08-04T19:07:56Z")

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I have an application where I am communicating to Ignition via MQTT.

At Ignition I’m referencing the MQTT tag to a UDT (using a reference tag) to apply additional data and then historicize it in Ignition.

My question, with MQTT buffering, will it still buffer data into the historian if I do the referencing to another tag? Or will the buffering break and I’ll see a gap in data?

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**Author:** ![kcollins](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kcollins/32/19646_2.png) [@kcollins](https://forum.inductiveautomation.com/u/kcollins)\
**Post date:** [August 4, 2022, 9:14pm UTC](https://forum.inductiveautomation.com/t/mqtt-historian/62695/2 "2022-08-04T21:14:05Z")

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I think this thread discusses your specific question: [[FEATURE] Allow reference tags to receive backfill data from sources like MQTT tags](https://forum.inductiveautomation.com/t/48261)

I’ve not had a chance to check in on this behavior, but there I’m pretty sure there was a point in time in the past where the history was _only_ on the base MQTT tag, requiring some custom functionality to indirect over to it for history queries (associated with your UDT). Last time I worked with this specific scenario was back in the 8.0.x days (and associated MQTT module versions of that time).

EDIT: just for clarity, the situation I mentioned above had History enabled on the MQTT Engine tag (and not the reference tags in the UDT). That used to be the only way I could get the backfill working properly.

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**Author:** ![nminchin](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/nminchin/32/6911_2.png) [@nminchin](https://forum.inductiveautomation.com/u/nminchin)\
**Post date:** [August 5, 2022, 2:00am UTC](https://forum.inductiveautomation.com/t/mqtt-historian/62695/3 "2022-08-05T02:00:53Z")

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> [@kcollins](#):
>
> just for clarity, the situation I mentioned above had History enabled on the MQTT Engine tag (and not the reference tags in the UDT). That used to be the only way I could get the backfill working properly.

Yep, this is what we're using as well, since backfill data does not get forwarded onto the reference tags. It's a bit of an ugly setup.