Run the Distributed Action Handler in Non-Mirror Mode

In non-mirror mode, the IDOL Servers that the DAH distributes ACI actions to are different (that is, each IDOL Server is configured differently and contains different data). If you run the DAH in non-mirror mode, you must set up virtual databases, which can be of the following types:

  • Combinator. The virtual database forwards an action to all the databases that it represents. It collates and sorts the results before it returns them.

  • Distributor. The virtual database forwards an action according to the selected distribution method to one of the databases it represents:

    • Load balancing. Each distributor VDB assigns each incoming action to just one of the databases that it maps to. When this database responds with a result, the DAH forwards it to the client software.

      If an IDOL Server stops responding for any reason (for example, because of a hardware failure or network outage), the DAH marks it as down. It assigns incoming actions only to the databases on IDOL Server installations that are running, saving the time that it takes to attempt to communicate with the failed database.

    • Failover. Each distributor VDB forwards incoming actions to the first database that is listed for the virtual database MapsTo parameter. If this database stops responding for any reason (for example, because of a hardware failure or network outage), the DAH marks it as down and switches to the next database (the second one listed for the MapsTo parameter) and so on, and seamlessly continues to service client actions.

Virtual databases can map to IDOL Server databases or to other VDBs that you set up for the DAH.

NOTE: When you implement a non-mirror mode architecture in which VDBs map to other VDBs, set up combinator VDBs to map only to other VDBs. Distributor virtual databases normally map directly to the databases on the servers. (That is, the combinator VDB combines results from distributor VDBs; a distributor VDB must not distribute queries to combinator VDBs.)

For details of the actions that the DAH can distribute in non-mirror mode, see IDOL Server Actions.