This topic is about Configuration Change CRCs and Configuration Change Group CRCs that can be used to monitor user-instigated configuration changes. These CRCs are different to the Configuration CRCs that ClearSCADA uses internally for synchronization and other purposes. (The internal Configuration CRCs are unaffected by enabling or disabling the Configuration Change CRC feature.)
Every item in the database is assigned a Configuration Change CRC value. You can enable the Configuration Change CRC feature so that this cyclic redundancy check (CRC) value is recalculated whenever the item's configuration changes. The triggers for a change in CRC value comprise any of the following:
- The item's writable configuration changes
(Writable configuration comprises properties for which you can change the value manually in the database, as opposed to Read-Only configuration that is read from the database.) - The item's type changes (for example, from one type of point to another, using the Convert To feature)
- The item's individual security settings change
(The item's Configuration Change CRC value is unaffected by security changes that it inherits from elsewhere.) - The item's individual default colors change (for example, via the Color Palette)
(The item's Configuration Change CRC value is unaffected by changes to default colors that it inherits from elsewhere.) - You upgrade to a different version of ClearSCADA and that version results in changes to the item's writable configuration (such as further properties being added to the item's configuration Form).
Groups, Group Templates, and Group Instances additionally have a Configuration Change Group CRC that changes whenever that group's configuration, or the configuration of any items in that group or any sub-groups, changes (providing that the Configuration Change CRC feature is enabled). The triggers for a change in CRC value are the same as those listed for Configuration Change CRC values above.
In addition to the above, if the configuration of a Group Template changes, this will result in the Configuration Change CRC and Configuration Change Group CRC values changing in both the Group Template and the Group Instances that reference that Group Template.
Two database items of the same type, with the same name, and the same configuration (including references to other items in the database), on a system running the same version of ClearSCADA, will have the same Configuration Change CRC value. The CRC values of a Group Template and its Group Instances will differ, and as such, the CRC values of a Group Template and its Group Instances are not directly comparable.
When the feature is enabled, ClearSCADA uses the Configuration Change CRC and Configuration Change Group CRC values to determine whether an item or group's configuration has changed. System administrators may also find the CRC values useful for detecting whether configuration remains unchanged, such as in the following scenarios:
- Determining whether an archive or backup contains configuration that is unchanged from that in the online database
- Determining whether the configuration in an sde (database export file) matches that in an online database. For example, in the situation in which an sde is used to replicate content in another ClearSCADA database - identical CRC values provide confidence that the configuration in the online database is unchanged from when the sde was produced.
- Determining whether the configuration differs between one online database and another that has a very similar database structure (providing that both systems are running the same version of ClearSCADA).
For more information, see Determine which Items in a Group have Changed Configuration, and see Ascertain which Configuration has Changed.
If you intend to use Configuration Change CRC values to determine whether configuration changes have occurred, remember to take a new 'snapshot' of the relevant archives, backups, or sdes whenever you upgrade your system (as various CRC values might have changed on upgrade).
If you change an item's configuration, but then change that configuration back again, the item's Configuration Change CRC value will revert back to the value that existed before the configuration change was implemented and then reverted. However, the item's Last Modified status attribute will change to show the date that the item's configuration last changed (even if that change resulted in the configuration reverting back to its previous setting).
Further Information
The Convert To feature: see Converting a Database Item in the ClearSCADA Guide to Core Configuration.
Group Templates and Group Instances: see Group Templates and Group Instances in the ClearSCADA Guide to Core Configuration.