hub: efficient Device Twin Synchronization #1005
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Danielius1922
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In order to monitor resource changes and determine if a resource has been modified on the device, the CoAP gateway utilizes the Entity Tag (ETAG) mechanism. For Batch Observation, the ETAG is associated with the overall state of resources. Prior to initiating resource observation, the CoAP gateway retrieves the latest ETAG among all device resources from the Hub Database. When initiating the resource observation, the CoAP gateway sends the ETAG to the device. If the received ETAG matches the highest ETAG among the device resources, the device responds with a code VALID. However, if the received ETAG does not match, the device responds with a code CONTENT and includes the current ETAG. Consequently, when a resource changes, the device sends the updated ETAG back to the CoAP gateway via a notification. The CoAP gateway transmits the ETAG together with the Content by using the NotifyResourceChanged method to the resource-aggregate. This command is then converted into a ResourceChanged event, which is saved in a database and distributed through the event bus. In cases where multiple resources change simultaneously, the CoAP gateway updates all affected resources with the same timestamp and ETAG. The special query to the database efficiently retrieves the latest ETAG value from all device resources without loading the complete set of data. This optimized query solely focuses on performance and retrieves only the required ETAG value, excluding any additional information.
Force resynchronization refers to the process of refreshing all resources from the device and updating the twin. Its primary purpose is to resolve potential synchronization issues and ensure there are no operational discrepancies between the device and its twin. It also enable twin.
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resource-aggregate/cqrs/eventstore/mongodb/getLatestDeviceETAG.go
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ondrejtomcik
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In order to monitor resource changes and determine if a resource has been modified on the device, the CoAP gateway utilizes the Entity Tag (ETAG) mechanism.
For more information, please refer to the documentation.