One of the few errors taht strikes fear in the heart of a DBA is the dreaded:
ORA-01555 snapshot too old
ORA-22924 snapshot too old
Of course there are plenty of blogs instructing the DBA to simply “increase the undo_retention”, and there are cases where this works as expected. However, LOBs can be different as two different mechanisms exist for undo management. A LOB column can be configured to use retention to manage before mages of the data, but that can be confusing as each LOB column MAY have its own retention setting. The DBA_LOBS view reports whether LOG column uses retention or pctversion to manage undo, and the associated setting being used. Let’s -dig into this a bit deeper.
Read on to learn more about how LOB retention works, the types of issues you can run into with it, and how to correct those issues.