Distributed Action Handler 25.2
Distributed Action Handler Help

# Run the Distributed Action Handler in Mirror Mode

In mirror mode, the DAH distributes ACI actions to identical child servers (that is, all the child servers have the same configuration and contain the same data).

DAH can distribute all actions in mirror mode. For details of the available actions in each component, refer to the component Help, such as the Content Component Help.

Related Topics

- Display Online Help

To run the DAH in mirror mode

1. Open the DAH configuration file in a text editor.

2. Find the MirrorMode setting in the `[Server]` section, and set it to `True`.

3. In the `[Server]` section, set the DistributionMethod setting to one of the following options. This setting determines how the DAH distributes actions to the connected child servers:

   -     DistributionMethod=0

     Failover distribution method. The DAH forwards incoming actions to the first child server that you list in the DAH configuration file `[DistributedEngineN]` section. This server is the primary server.

     If this child server stops responding for any reason (for example, because of a hardware failure or network outage), the DAH marks it as down. It switches to the next child server (the second one listed in the `[DistributedEngineN]` section), which becomes the primary server, and so on, and seamlessly continues to service client actions. You can also manually set the primary server by using the EngineManagement action.

     If the child server comes online again (for example, because the hardware has been rebooted or the network connection repaired), the DAH adds it to the list of active child servers. However, it continues to use the new primary server unless that server stops responding, or unless you manually change the primary server.

   -     DistributionMethod=1

     Load balancing distribution method. The DAH assigns each incoming action to just one of the connected child servers (using a cumulative predictive algorithm that spreads the action load efficiently). When this child server responds with a result, the DAH forwards it to the client software.

     If a child 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 child servers that are running, saving the time that it takes to attempt to communicate with the failed child server.

     If the child server comes online again (for example, because the hardware has been rebooted or the network connection repaired), the DAH adds it to the list of active child servers. The child server again becomes a valid choice for actions.

   -     DistributionMethod=2

     View documents by reference distribution method. The DAH uses the distribute by reference distribution method. You can use this method only to distribute `View`, `GetLink`, and `ViewGetDocInfo` actions in mirror mode. The DAH distributes `View` and `GetLink` actions between View components based on the reference of the document to view. Actions that request the same document are then always sent to the same View component.

     When View first receives a request to view a document, it caches any embedded images in the result document. When you distribute between View components, using distribute by reference ensures that each document is cached in only one View component. The cached image is then used in subsequent requests for the same document.

4. Save and close the configuration file.

5. Restart the DAH for your changes to take effect.

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Version 25.2 | Last updated April 2025

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Product: Knowledge Discovery Distributed Action Handler 25.2

Topic Title: Run the Distributed Action Handler in Mirror Mode