Distributed Action Handler 26.1
Distributed Action Handler Help

# DistributionMethod

The method for distributing actions. Set `DistributionMethod` to `0` for failover, and `1` for load-balancing. The `DistributionMethod` determines how the DAH distributes actions if:

- it is run in mirror mode

- it is run in non-mirror mode, using Distributor VDBs databases

Type one of the following to determine which distribution method the DAH uses:

- 0. The DAH uses the Failover distribution method. Depending on the mode the DAH is run in, this method distributes actions as follows:

  - Failover in mirror mode. The DAH forwards incoming actions to the first child server that is listed in the DAH configuration file `[DistributedEngineN]` section. This server is the primary server. If this child server stops responding for any reason (for example, a hardware failure or network outage), the DAH marks it as down and switches to the next child server (the second one listed in the `[DistributedEngineN]` section), which becomes the primary server, and so on, seamlessly continuing to service client actions. You can also manually set the primary server by using the EngineManagement action.

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

  - Failover in non-mirror mode with server groups. The DAH forwards incoming actions to the first child server that is listed in the DAH configuration file for each child server group (that is, the first server listed in the Host parameter in the `[DistributedEngineN]` section). This server is the primary server. If a primary server stops responding for any reason (for example, a hardware failure or network outage), the DAH marks it as down and switches to the next child server (the second one listed in Host parameter in the `[DistributedEngineN]` section), which becomes the primary server, and so on, seamlessly continuing to service client actions. You can also manually set the primary server by using the EngineManagement action.

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

  - Failover in non-mirror mode with VDBs. The Distributor VDBs forward incoming actions to the first child server database that is listed for the virtual database MapsTo parameter. If this child server database stops responding for any reason (for example, a hardware failure or network outage), the DAH marks it as down and switches to the next child server database (the second one listed for the MapsTo parameter) and so on, seamlessly continuing to service client actions.

    The DAH periodically checks child servers that are down. If it finds that a child server has come online again (for example, because the hardware has been rebooted or the network connection repaired), it adds it to the active list of child servers. This child server database takes over as the sole destination for actions (as it takes precedence over the child server database that is currently serving results).

- 1. The DAH uses the Load balancing distribution method. Depending on the mode the DAH is run in, this method distributes actions as follows:

  - Load balancing in mirror mode. The DAH assigns each incoming action to just one of the child servers that it connects to (using a cumulative predictive algorithm that is designed to spread 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, a hardware failure or network outage), the DAH marks it as down and assigns incoming actions only to the child servers that are running, saving the time it takes to attempt to communicate with the failed child server.

  - Load balancing in non-mirror mode with server groups. The DAH assigns each incoming action to just one of the child servers in each server group (using a cumulative predictive algorithm that is designed to spread 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, a hardware failure or network outage), the DAH marks it as down and assigns incoming actions only to the child servers that are running, saving the time it takes to attempt to communicate with the failed child server.

  - Load balancing in non-mirror mode with VDBs. The Distributor VDBs assign each incoming action to just one of the child server databases that they map to (using a cumulative predictive algorithm that is designed to spread the action load efficiently). When this child server database responds with a result, the DAH forwards it to the client software.

    If a child server stops responding for any reason (for example, a hardware failure or network outage), the DAH marks it as down and assigns incoming actions only to the child server databases that are running, saving the time it takes to attempt to communicate with the failed child server database.

  The DAH periodically checks child servers that are down. If it finds that a child server has come online again (for example, because the hardware has been rebooted or the network connection repaired), it adds it to the active list of child servers. This child server database becomes a valid choice for actions again.

- 2. The DAH uses the distribute by reference distribution method. You can use this method only when distributing `View`, `GetLink`, and `ViewGetDocInfo` actions in mirror mode. The DAH distributes `View`, `GetLink` and `ViewGetDocInfo` actions between view servers based on the reference of the requested document. All 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 distributing between View components, use distribute by reference mode to ensure that each document is cached in only one View component, and it uses the cached images in subsequent requests for the same document.

Type: | Long
Default: | 1
Required: | No
Configuration Section: | Server
Example: | `DistributionMethod=0`
See Also: | LoadBalanceMethod MirrorMode TimeBetweenRetries

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Version 26.1 | Last updated January 2026

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Product: Knowledge Discovery Distributed Action Handler 26.1

Topic Title: DistributionMethod