Settings Synchronization Options

Option

Description

Synchronization Mode

There are several synchronization modes available:

• Normal Synchronization. The value of the setting is synchronized between Iotellect Server and Device during every synchronization cycle.

• Synchronization Disabled. No synchronization is performed for this setting.

• Device to Server Only. Forces the server to make server-side value read-only and disable device write operations for this setting. This is useful when a device/driver report setting as writable, but the actual write operations fail (e.g. due to insufficient permissions).

• Direct Device Access. The value of the setting is read directly from Device when it is requested by system components. If some system component tries to modify system values, changes are also written directly to the Device. With this setting, read/write operations may fail if Device I/O fails or the Device returns an error.

• Direct Device Writes. Same as above, but applies only to write operations. Value reading is performed from the settings cache, same as in Normal Synchronization mode.

• Use Server-Side Master Value. In this mode, server-to-device synchronization is always performed for this setting. Data Table returned by the Master Value Expression (see below) is pushed into the device instead of the value taken from the settings cache.

• Ignore Modification Time. Ignores both server-side and device-side setting modifications timestamps. The setting is synchronized from server to device if the value was changed on the server and from device to server otherwise.

• Custom. Uses a custom synchronization handler provided by the system, if any. This mode is usually enabled automatically by the system if a custom handler is available, but may be overridden by a human.

History Storage Time

If this option is set to a non-zero value (i.e. update history saving is enabled) a persistent Change event will be generated every time when setting value is modified in the server cache. This may happen if a new value differing from the previous one is read from a remote device or some system component modifies the cache. Change event contains value of the variable, so its history may be used as a source data for reports and charts. Saving of history is disabled by default to prevent an avalanche-like increase in database size.

History Mode/Rate

Defines which values are saved to the device snapshot and history storage.

If History Mode/Rate is set to zero or one of the negative integers listed below, historical values will be saved according to the indicated conditions. A value is considered “new” if it differs from the most recently recorded historical value. Variable quality refers to the quality code assigned by the physical device or the device driver. Default codes are assigned by Iotellect Server core if no code was assigned by the device or driver.

• 0: All “Good” Quality Values. Only “good” quality value will be saved to history, including values that are identical to the previously recorded historical value.

• -1: New “Good” Quality Values. Only “good” quality values will be saved to history, and only if the value differs from the most recently recorded historical value.

• -2: New Values, Except “Bad Not Connected” Quality. New values of any quality will be recorded to history, except for values with the specific “bad“ quality “not connected”, which will be excluded.

• -3: All Values of “Good” or “Bad Not Connected” Quality. All “good” quality values and the specific “bad“ quality “not connected” will be recorded.

• -4: All Values, Except “Bad Not Connected” Quality. All values of any quality will be recorded to history, except for values with the specific “bad“ quality “not connected”, which will be excluded.

• -5: New Values. Values of any quality will be recorded to history, except for values that are identical to the previously recorded historical value.

• -6: All Values. All values of any quality will be recorded to history.

The quality of a variable can be accessed through the Data Table Properties standard reference quality. For example, the quality of a variable named exVar of a device with context path users.admin.devices.exDevice can be references in an expression with {users.admin.devices.exDevice:exVar#quality}.

If History Mode/Rate is set to any positive integer number, historical values will be saved to a database only every Nth synchronization cycle, where N is the value of History Rate. However, Update events are generated on every synchronization cycle and interested parties will be notified about all value changes.

You can also control a way how the system is notified about value updates: on every variable value update or on change only (see Deliver Updates).

If History Storage Time is not set (i.e. history is not stored), the synchronization period is rather short and the setting itself has complex format (e.g. many fields or nested tables), setting History Mode/Rate to All “Good” Values may improve performance, since server won't load old cached value and compare it with a new one during every synchronization.

Change Event Timestamp

Defines how the server saves timestamps of variable change events. Options are as follows:

• Use Driver/Device Timestamps (Default value): If the device or driver provides a timestamp for the new variable value (for example, a sensor noting the moment it took a measurement), this timestamp will be used for the variable change event. This option prioritizes accuracy in reflecting when the actual measurement occurred, regardless of any network latency or delays when recording data in the database. If the device or driver does not provide a timestamp, the server timestamp is used.

• Use Server Timestamps: The variable change event timestamp is assigned by the server based on when the data was recorded in the database. This can simplify certain types of analysis, especially if the focus is on when data arrived at the server rather than when it was originally measured.

Synchronization Period

This option may be used to define a custom synchronization period for a certain setting. The default value is NULL (<Not set>), so the setting value is synchronized during the full synchronization cycle. The custom period is useful when it's necessary to read some fast-changing data from the Device.

Cache Mode

Advanced option. Defines the location of the settings cache for the variable. The selected Cache Mode for a variable takes precedence over the Default Cache Mode selected in Generic Device Properties. Options are the same as those of Default Cache Mode, with the addition of the following:

• Default (Use Default Cache Mode Setting): Default option that causes the variable to be cached according to the Default Cache Mode value selected in Generic Device Properties.

Deliver Updates

This flag controls sending variable Update events. When enabled a variable Update event will be fired on each synchronization, even if the variable value remains the same (see History Rate).

Condition

If this condition expression is defined, the synchronization will be skipped if it returns false. It is useful for disabling synchronization during maintenance, night hours, etc.

Default Context

Context of the current device.

Default Data Table

Current variable value stored in the settings cache.

Default Row

0

Environment Variables

Standard variables only.

Filter

If this filter expression is defined, it will be used to filter out values coming from both device and server:

• If value is being synchronized from device to server and filter expression returns FALSE, the value won't be written into server cache. This helps to treat some device-provided values as "bad" and drop them out.

• If a value is being synchronized from device to the server and the filter expression returns a Data Table, it will be treated as a converted device setting value. This converted value will be written into the server cache and history, instead of the value returned by the driver. This is suitable for filtering tabular data, range normalization, etc.

• If a value is being changed by a system operator, server component, or external system and the filter expression returns FALSE, the change request fails with an error.

Default Context

Context of current device.

Default Data Table

Current value, either taken from device or provided by system operator, server module or external system.

Default Row

0

Environment Variables

Standard variables only.

Example: abs({.:temperature$celsius} - {celsius}) > 0.5

This filter expression compares celsius temperature retrieved during the previous synchronization with the new value just received from a device. The synchronization is performed only if their difference exceeds 0.5 degrees, allowing to avoid chattering of server-side value.

Master Value Expression

An expression used to retrieve the value to be written into the device if Use Server-Side Master Value synchronization mode is enabled.

Default Context

Context of current device.

Default Data Table

None.

Default Row

0

Environment Variables

Standard variables only.

Add Previous Value To Variable Update Event

The flag indicating that the variable's Updated event will contain previous variable value.