Creating and Editing Rollback Segments
Rollback Segments allow you to undo, or rollback, DML transactions such as SQL deletes, inserts, and updates that have been executed on a database. A rollback segment entry contains information about the database records before they were modified by a transaction.
The following database platforms support rollback segments:
Create or Edit a Rollback Segment
- In the Data Model Explorer, expand the Physical Main Model, right-click the Rollback Segments node, and then click New Rollback Segment.
- Complete the Rollback Segments Wizard and then click Finish to create the Rollback Segment.
TIP:: Once you have created the auxiliary table, you can edit it by right-clicking the rollback segment you want to change, and then clicking Edit Rollback Segments.
- Should this rollback segment be made public? This option only applies to a database operating in a parallel server environment. A public rollback segment can be brought online by any instance of the database in a parallel server environment. A private rollback segment can only be brought online by the database instance that has the rollback segment specified in its initialization file.
- What extent sizes do you want to assign to this rollback segment?
The before-image details for multiple transactions can be recorded in one rollback segment but each transaction must fit entirely into one segment and the blocks of a rollback segment are not overwritten until the transaction that wrote to those blocks has been committed. You must therefore, ensure the rollback segment is big enough to hold all the information for the longest running query without wrapping and is big enough to hold the undo information for the largest transaction x number of concurrent transactions ÷ number of rollback segments.
- The default extent size is the size of 5 data blocks. The default minimum extent size is the size of 2 data blocks. The maximum extent size varies by operating system.
- Optimal Size: The optimal extent size cannot be less that the space initially allocated for the rollback segment.
- What are the minimum and maximum number of extents...? The default minimum number of extents is 2.The default maximum number of extents varies by operating system.
Enter or edit a definition for the rollback segment. If the target database supports it, ER/Studio Data Architect adds this definition as a comment when generating SQL code.
Displays the CREATE ROLLBACK SEGMENT statement needed to build the rollback segment. ER/Studio Data Architect uses the platform-specific parser of the model's selected database platform to generate the rollback segment.
Attachment Bindings tab
Bind an external piece of information, or attachment to the rollback segment. You can also remove an attachment from an object, override an attachment binding's default value, or change the position of a bound attachment. To override the value of the attachment you have moved to the Selected Attachments grid, double-click the Value field of the target attachment. ER/Studio Data Architect opens the Value Override Editor or a list depending on the attachment datatype. Attachments are created in the Attachments folder of the Data Dictionary. For more information, see Attaching External Documents to the Data Model.