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If you do not select In-Order History, data will be lost/ignored at MQTT engine because Ignition will ignore writes to the Tag if the timestamp on the Tag change is older that the current value.

Whilst the history flush is in progress, all new change events are written to the history store until it has been completely flushed. If the tag change rate at the Edge is faster than the MQTT Transmission Flush Period this can cause a build up of data in history store(s) and prevent the publishing of live data. 

History Configuration Persistence


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. 

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CLD80:FAQ: Ignition ModulesCLD80:
FAQ: Ignition Modules