High availability policies for the transaction service

WebSphere® Application Server provides integrated high availability (HA) support in which system subcomponents, such as the transaction service, are made highly available. An HA policy provides the logic that governs the manner in which each WebSphere Application Server HA component behaves within the overall HA framework. For the transaction service, the transaction HA policy provides the logic to determine which servers own a recovery log at any time.

Typically, transaction policies assign ownership of a recovery log to the server that originally created it (the home server) and that server can then use the recovery log for both recovery and normal transactional activity. In the event that the home server is unavailable or fails, ownership can pass to a peer server to undertake recovery processing.

Conceptually, a policy can be thought of as consisting of two key components, a policy type and a policy configuration.

Policy type

The policy type determines whether peer recovery initiation is manual or automated. The policy essentially provides the logic for determining updated recovery log ownership in the event of a server failure. The following WebSphere Application Server policy types are used for transaction peer recovery (other HA policy types exist, but are not used by the transaction service):

Static: Ownership of the recovery log is defined in the WebSphere Application Server configuration. At run time, the static policy assigns ownership accordingly. Any changes to ownership require a change to the static configuration and therefore this policy type is used for manually initiated peer recovery.
One-of-N: Ownership of the recovery log is determined dynamically by the WebSphere Application Server HA framework and assigned to exactly one of the N cluster members. This policy type is used for automated peer recovery.