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In order to cover data loss during a keep alive timeout scenario, the MQTT Transmission History Store includes a Rolling History Buffer that can be configured in the Advanced Properties configuration section. When the Rolling History Buffer is enabled, all tag changes will be written to the History Store regardless of connection status.
The quantity of tags stored during an active connection, age of the data and frequency of purge can all be configured such that on the Prune Interval, the Prune Quantity of the oldest data over the Max Age will be deleted.Metrics Stored tag for the History Store will update as data is written to and pruned from the Rolling History Buffer.
The In-Order History configuration parameter of the Transmitter will determine whether the data is flushed in-order (synchronously) or asynchronously.
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Data stored in the Rolling History Buffer for an In-Memory History Store will not be persisted across a module configuration change, module disable/enable, module restart or power loss. Data stored in the Rolling History Buffer for a Disk-Backed History Store will persist across a module configuration change, module disable/enable, module restart or power loss however you will lose change events that occur during the update or refresh. |
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It can take MQTT Transmission 1.5 times the configured Server Keep Alive time to determined that there is a connection failure. |
Tip |
The Rolling History Max Age should be at least 2x the Transmitter Server Keep Alive timeout |
Warning |
Dependent on the configuration values and the frequency of tag change data, system performance may be impacted when using the Rolling History Buffer to ensure that all tag change events are captured during this period. |
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Using this feature may result in duplicate tag change event data being reported to Ignition as there is the potential for the publish of historical data that was previously successfully received. This will generate errors reported by the StoreAndForward.Sink.HsqlDataStore.DatasourceForwardTransaction logger when inserting the data into a database. These are benign errors and will not result in data loss. |
Warning |
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Dependent on the configuration values and the frequency of tag change data, system performance may be impacted when using the Rolling History Buffer |