16.10 - Automatic Failover Conditions - Teradata Unity

Teradata Unity User Guide

Product
Teradata Unity
Release Number
16.10
Published
January 2018
Language
English (United States)
Last Update
2018-03-29
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Automatic Failover Parameters

If during this wait period the active Sequencer is running, a Sequencer will not failover. The HAAutoFailoverWait parameter defines the number of seconds the Watchdog process must wait before initiating a failover. The default and minimum value is 300. A value of 0 disables the wait period checking. TheHAAutoFailoverCondition parameter defines the checks before the standby Sequencer automatically takes over; the default value is 7.

Automatic Failover Component Values

The HAAutomaticFailoverPrerequisitesMode parameter is the sum of the component values for the prerequisites enabled. Enabling all prerequisites in the following table result in HAAutomaticFailoverPrerequisitesMode = 7 (1 + 2 + 4).
It is strongly recommended not to change the default values, or to disable one or more of the checks mentioned above.
Component Value Description
1 The standby Sequencer must connect to all systems that were connected before losing the active Sequencer. This prerequisite checks for a potential network issue.
2 Sequencers periodically connect to all managed systems. These connections are logged on the managed systems. A Watchdog must wait a defined time before issuing a Sequencer failover. During this time, the standby Sequencer confirms that the active Sequencer has not connected to any managed systems. This prerequisite ensures the active Sequencer has not been connecting to any managed systems.

If HAAutomaticFailoverWait = 0, this prerequisite cannot be performed.

4

Dispatchers log transactions on all managed systems. A Watchdog waits before issuing a Sequencer failover. During this time, the standby Sequencer confirms the transaction tables have not been updated on any managed systems. An updated transaction table signals that the Dispatcher is working which may indicate the active Sequencer is still running. This prerequisite ensures a transaction has not been committed before appointing a new active Sequencer. This prerequisite reduces the chance of an irreconcilable Split Brain.

If HAAutomaticFailoverWait= 0, this prerequisite cannot be performed.