Cursor stability ensures that any row that has been changed by activation group with a dissimilar commitment definition cannot be read before committing.
In IBM Db2, cursor stability is one of the isolation levels that can be set for transactions. Isolation levels determine the visibility of changes made by one transaction to other transactions. Cursor stability is a medium level of isolation.
In the context of cursor stability in Db2:
- Read Stability: A cursor that is opened with cursor stability allows the cursor to see the data committed before the cursor was opened. However, it does not lock the rows it fetches. This means that other transactions can update or delete the rows being fetched by the cursor, but the changes are not visible to the cursor.
- Cursor Movement: The cursor stability level locks the rows that are fetched only for the duration of the fetch operation. Once the fetch is complete, the locks are released. This allows other transactions to update or delete the same rows without waiting for the cursor to be closed.
- Concurrency: Multiple cursors opened with cursor stability can access and fetch rows simultaneously, and they do not block each other.
- Commit and Rollback: Changes made by other transactions after the cursor is opened are not visible to the cursor until the cursor is closed. If a transaction is rolled back, the changes made by that transaction are also not visible to the cursor.
In summary, cursor stability in DB2 allows for a balance between concurrency and consistency, allowing multiple transactions to access and fetch rows simultaneously without locking the rows for an extended period. However, changes made by other transactions after the cursor is opened are not visible until the cursor is closed.