[Online lesson excerpt] 4. Demonstrate a scenario that causes ora-01555 errors

1 Creating an Undo table space

2 View current undo Configuration

3 The default undo table Space

4 Confirm configuration of Changes

5 Creating a test table

6 Analog Bulk Operations

7 query 2 minutes ago Data

From here to when the query 2 minutes before the data, the system reported ORA-01555 error, indicating that the snapshot is too old. This error occurs because the set of rollback segments is too small and the rollback segment is recycled, a pre-image of the data needs to be sketched from the rollback segment at some point before the query, because the rollback segment of the image before saving the data has been overwritten, causing the query to fail to achieve consistent read, Report a ORA-01555 error.

[Online lesson excerpt] 4. Demonstrate a scenario that causes ora-01555 errors