Data Backfill is a feature that is available optionally for our Temperature sensor and is a standard inclusion for our Temperature Probe sensors and Temperature & Humidity sensors.
Where to use?
Data Backfill operates reliably in stable and permanent installations, with good and reliable connectivity as a requirement.
While it is primarily designed to prevent data loss during unexpected interruptions (service interruptions, power outages, etc.), it can also handle planned disconnections or be used in data logging scenarios. However, this requires that a stable connection be re-established after offline periods. However, this is not its intended purpose, and consistent connectivity is recommended for optimal performance.
How does it work?
If the sensor goes offline, it will start storing measurements locally until the connection to the cloud is restored. The sensor will then start backfilling data, starting with the most recent samples first. The sensor will overwrite the oldest data if the memory becomes full.
The number of data points that can be stored in an offline period depends on the sampling rate, heartbeat configuration, and temperature fluctuations.
The Temperature sensor has a storage capacity of up to 100,000 events, while Temperature Probe sensors can store up to 50,000 events. Temperature & Humidity sensors can store up to 31 days of data.
The backfill duration remains unaffected by the sampling rate. Touching the sensor will not speed up the backfilling process.
How long does it take?
During the first 48 hours after connecting to a Cloud Connector, data is backfilled at a rate of 1 HBI per second.
It takes at least two heartbeats for backfilling to start after sensor reconnection to the Cloud Connector:
- One to trigger the retrieval request
- Another for the sensor to respond.
You can use the following simple formula to determine the time required for data backfill:
Minutes of offline time ÷ HBI = Time needed for backfill in seconds (after the 2nd HBI)
If all the data is not backfilled within the first 48 hours, the backfill rate will then slow to approximately 20 backfilled HBIs for every 1 HBI.
Whether the reported Temperature event was due to Backfill or not is currently only visible through the API. The event contains a field called isBackfilled and is documented in our Developer Docs. This is not yet available in Studio.