True Primary Data Center Outage | Teradata Unity - 17.00 - True Primary Data Center Outage - 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
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When the entire primary data center, which houses the Unity server with the active sequencer, is down and the issue cannot be resolved in a short time, the standby sequencer located on the second Unity server (usually located in a second data center) can take over the role of the active sequencer. Use the SEQUENCER FAILOVER command at the unityadmin prompt for the second Unity server.
unityadmin> sequencer failover;
W Warning: SEQUENCER FAILOVER can cause client connection errors (but transactions will be completed).

W READ CAREFULLY! This command should only be executed when you have confirmed the active sequencer on the other unity server has been shutdown or is known to be DOWN.
W Do NOT use this command if the WAN between the two unity servers is down, (because the other unity server might still be up and processing connections).
W Have you:
W           1. Confirmed the other ACTIVE sequencer is DOWN, or other unity server is DOWN?
W           Or... 2. Halted all systems for a planned failover?

Takeover has succeeded. This sequencer is now ACTIVE.
unityadmin>
The SEQUENCER FAILOVER command helps to make sure the other Unity server is really shut down.

After the connectivity to the failed data center is restored, before allowing the Unity servers to reconnect to each other, make sure the old recovery log on the formerly active Unity sequencer is deleted.

If the connectivity to the failed data center is restored before the sequencer in that data center is reset, it may trigger a split-brain shutdown. Both sequencers must be shut down so an operator can choose an active sequencer. This helps to avoid missed transactions in the recovery log of the now active sequencer. The sequencer roles can be switched later during a planned outage.

Following the failover of the Unity sequencer, the endpoints on the standby Unity server start listening on their primary and standby IP addresses. Clients can then reconnect through this Unity server.