In the DAH, you can manage child servers (engines) either by directly changing configuration, or by using the EngineManagement action. If you change the configuration, you must restart the DAH, while the EngineManagement action allows you to perform the following administrative tasks while the server is running:
add child servers to the DAH
change the weight of a child server
power a child server up or down
check or set the primary server for failover distribution method
ping a child server
show the status of a child server.
You cannot use the EngineManagement action to remove a child server. Instead, you can either power it down, or remove it from the configuration file.
Child server weight is the relative proportion of actions that you want DAH to send to that child server. This weight is used only when you are using a weighted load balance method is set (that is, LoadBalanceMethod=2 and DistributionMethod=1). You might want to set weights if your child servers have different capabilities.
You might want to weight your child servers differently if one has a much more powerful CPU than the other, or if the child servers are tiered DAH servers that have different numbers of children.
Powering up or down tells the DAH whether to use a specified child server. For the weighted load balance method, powering down is similar to setting the weight to zero, except that a server with a weight of zero is still used if no other child server is available.
You might want to power down a child server if you know that it is not running, so that DAH does not waste resources attempting to send queries. You can also power a child server down when you are performing maintenance and you do not want to send queries to that child server. You can also use powering down in a system where you do not want to use a child server for indexing and querying at the same time, to maximize the resources available for either indexing or querying. In this case, you power down a child server when you want to use it for indexing.
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