ClearSCADA's Configuration Transaction feature is designed to block certain changes to items in Group Templates and Group Instances when updates are pending. This restriction helps to avoid ‘race conditions’. A race condition is where two or more tasks attempt to access the same resource at the same time with unpredictable results. For example, a user could make configuration changes to items in a Group Instance that has updates pending. While the user is making the changes, the update occurs. This causes a race condition as the update and the user are trying to access the same resource at the same time. This can result in the changes made by the user being overwritten by the update.
The Configuration Transaction feature restricts users from performing certain tasks while transactions are pending, including:
- Changing the configuration or structure of items in a Group Instance that has changes pending (this includes exporting an item in a Group Instance).
For more information on configuration changes and structure changes see Configuration Changes and Structure Changes.
- Renaming or moving items within a Group Template that has configuration changes pending. (If a Group Template only has structure changes pending, you can rename or move items within the Group Template as and when required.)
You can move items into or out of a Group Template that has configuration changes pending.
To help prevent the most common causes of ‘race conditions’, ClearSCADA uses a pending transactions count. By using this count, ClearSCADA can determine if there are further updates to be applied (see Pending Transaction Count).
The Transactions section of ClearSCADA’s Server Status Tool provides details about any Group Template and Group Instance transactions while those transactions are pending or in progress:
Further Information
Transactions Section of the Server Status Tool: see Transactions in the ClearSCADA Guide to the Server Status Tool.