75 ways to demystify DB2: #29: Techtip : What is a tiebreaker in DB2 HA (High Availability)?

Body

Rocks, Paper, Scissors?

Heads or Tail?

Good guess's but none of the above.

A tiebreaker is a object used in a DB2 HA (High Availability) cluster environment comprised of even number of nodes.

In such a cluster environment, when both nodes cannot communicate with each other, the tiebreaker is used by both nodes to see which node is still active and can continue to host cluster resources.  This in essence, is "breaking a tie", hence, a tiebreaker.

Tiebreaker requirements

• A tiebreaker must be accessible from all nodes in the cluster.
• A tiebreaker is accessed at network partition time by all surviving nodes to determine the winning subcluster.
• If a node is able to access the tiebreaker resource, then that node is considered to be part of the winning subcluster.
• Nodes that are unable to access the tiebreaker are considered part of the losing subcluster and are shut down.
• The ideal tiebreaker is stateful, in the sense that the tiebreaker object allows only one node access to it at any one time.
• For an ideal tiebreaker, acquisition must be a fast and reliable operation.

There are three types of tiebreakers that can be used with DB2 HA, network, disk and cloud.

Stay tuned to this blog for a forth-coming discussion on the three types of tiebreakers next.