Read-Only State | Teradata Unity - 17.00 - Read-Only State - Continuous Availability - Teradata Unity

Teradata® Unity™ User Guide

Product
Continuous Availability
Teradata Unity
Release Number
17.00
Published
September 2020
Language
English (United States)
Last Update
2020-09-15
dita:mapPath
fmz1594836948704.ditamap
dita:ditavalPath
qqk1595871525984.ditaval

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.