Read-Only State | Teradata Unity - Read-Only State - Continuous Availability - Teradata Unity

Teradata® Unity™ User Guide

Continuous Availability
Teradata Unity
Release Number
September 2020
English (United States)
Last Update
Product Category
Analytical Ecosystem

This state enables read access for an application when data is externally copied from the table and must remain unchanged.

For managed sessions, if a table is in a read-only state across all Teradata Database systems, Unity rejects the write with an error. If only a single Teradata Database system or a table on a specific Teradata Database system is in read-only state, then any write requests remain queued in the Recovery Log to be replayed when the Teradata Database system or table is placed into a restore state.

If a Teradata Database system enters a read-only state, all tables automatically enter a read-only state. If a table is read-only on one or more systems and a write occurs on this table (because the table is in read-write mode on at least one other active system), then the read-only state is changed to an interrupted state.

A table may also automatically be placed in read-only if a session encounters an error and the "Read-only on write failure" feature is turned on.

To change a table or system to a read-only state, run the SYSTEM FREEZE command. Unity holds any new transactions and waits for any in-flight transactions to close. The Dispatcher holds transactions for the time specified in the HaltTimeout parameter. If successful, the Teradata Database system or table becomes read-only. If an error occurs or if in-flight transactions do not finish successfully during the timeout, the operation aborts and the Teradata Database system or table remains in the active state.

From the read-only state, you can change a Teradata Database system or table into a restore state with the SYSTEM RECOVER command.