READ Locks and Cancelled Rollback Operations - Teradata Database

READ Locks and Cancelled Rollback Operations

When you use the RcvManager utility to cancel a transaction rollback, the system marks the base table on which the rollback was cancelled as nonvalid. As a result, the table cannot be updated. With some restrictions, you can inspect the rows of the non‑valid base table if you specify a LOCKING FOR READ OVERRIDE modifier.

The following rules document the restrictions on the use of a LOCKING FOR READ OVERRIDE modifier:

You can only read from a single base table using this modifier. Attempts to perform multitable operations return an error.

You can specify LOCKING FOR READ OVERRIDE for any single base table, whether a rollback has been cancelled on that table or not.

The Optimizer only uses indexes to read base valid base tables. If you use LOCKING FOR READ OVERRIDE to access a non‑valid table, then the system always uses a full‑table scan.