A table may be placed in the Read-Only state from an Active or Standby state if a session encounters an error and the Read-only on Write Failure feature is turned on.
With the Read-Only on Write Failure parameter enabled, when a INSERT to targetTable SELECT FROM sourceTable fails on the standby system, the targetTable is Interrupted and the sourceTable becomes read-only. As a result, no further writes to the sourceTable are allowed on the standby system until the INSERT-SELECT completes recovery. If a write occurs on the sourceTable, the table is interrupted on the standby system (need recovery).
The feature is used in ETL environments where data is loaded to a stage table, then moved to a base table, and finally moved to a target table. This feature is not needed for a reporting environment. For mixed environment, Teradata recommends enabling this feature.