1. Replication Guide
  2. Administering an Active Standby Pair Without Cache Groups
  3. Detection of Dual Active Databases

Detection of Dual Active Databases

Ordinarily, the designation of the active and standby databases in an active standby pair is explicitly controlled by the user. However, in some circumstances the user may not have the ability to modify both the active and standby databases when changing the role of the standby database to active.

For example, if network communication to the site of an active database is interrupted, the user may need the standby database at a different site to take over the role of the active, but cannot stop replication on the current active or change its role manually. Changing the standby database to active without first stopping replication on the active leads to a situation where both masters are in the ACTIVE state and accepting transactions. In such a scenario, TimesTen can automatically negotiate the active/standby role of the master databases when network communication between the databases is restored.

If, during the initial handshake between the databases, TimesTen determines that the master databases in an active standby pair replication scheme are both in the ACTIVE state, TimesTen performs the following operations automatically:

  • The database which was set to the ACTIVE state most recently is left in the ACTIVE state and may continue to be connected to and updated by applications.

  • The database which was set to the ACTIVE state least recently is invalidated. All applications are disconnected.

  • When the invalidated database comes back up, TimesTen determines whether any transactions have occurred on the database that have not yet been replicated to the other master database. If such transactions have occurred, they are now trapped, and the database is left in the IDLE state. The database needs to be duplicated from the active in order to become a standby. If there are no trapped transactions, the database is safe to use as a standby database and is automatically set to the STANDBY state.