Reconcile event_id and user_id in Amplitude

  • 8 January 2022
  • 1 reply




We have a microservice application, with each micro service sending events to Amplitude. All events will have a device_id, and some events will have both a device_id and a user_id in their JSON.

Let say we send 20 events to Amplitude. 10 of them have both an user_id and a device_id. 10 of them only have a device_id.

Will Amplitude automatically assign the missing user_id to events that didn’t have it? Or do we have to manage something by ourselves on Amplitude?


Thanks a lot and have a great weekend.



Best answer by SheenaGreen 8 January 2022, 21:38

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Once Amplitude associates a user ID to a specific device ID (which is done with the events that have both user_id and device_id), it will merge all historical/future events performed by the same device ID into the same Amplitude profile, even if the user ID was not present at the time the event was performed. 


So in your example, you shouldn’t need to manually assign user_id to the 10 events that only had device_id. All 20 events will automatically appear in the same Amplitude profile that has both user ID and device ID.