Device Snapshots (Settings Cache)

When Iotellect Server first reads values of the device's internal settings, it stores these values in the database. This is called creating a device snapshot or settings cache. The snapshot allows users to view and edit settings of the device even if it is not currently connected to the Iotellect Server.

NEW TERM: A cache is a collection of data duplicating original values stored elsewhere or computed earlier. A cache is used when the original data is expensive (usually in terms of access time) to fetch or compute, while reading the cache is "cheap" (i.e, easy and quick).

When you're viewing or editing device settings, you're actually working with the device snapshot. There is no way to edit the actual Device settings directly (unless direct synchronization mode is enabled). New settings are written to the device on the next synchronization.

The settings cache is periodically synchronized with the device. Synchronization occurs in the following cases:

  • When a device connects to the Iotellect Server

  • When setting values are changed in the cache (using Iotellect Client for example) while a device is connected to the server, if the Start Synchronization on Setting Change setting is set to true (which is the default value)

  • Periodically, as defined by the Synchronization Period setting

Every setting is synchronized according to the following algorithm:

  • If the setting value does not exist in the server cache, it is cached (i.e. its value is read from the device and stored in the server cache)

  • If the setting value in the server cache was changed later than in the device, the cached value is written to the device

  • If the setting value in the device was changed later than in the server cache, the cached value is replaced by the current value of the device setting

  • Otherwise, no action is performed

Device snapshot can be persistently stored in database or located in memory. This behavior is controlled by the Settings Cache Mode option located in generic device properties. If the Cache Mode is set to Database (which is the default setting), each device setting update causes an update of the underlying configuration storage. This leads to performance problems on highly loaded systems, so consider changing Cache Mode to Memory when the system is handling thousands of updates per second.

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