How the Rebalancer Moves Documents
There are many similarities between the rebalancing process and the reindexing process. Rebalancing is configured at the database level and individual rebalancing processes run separately on each forest.
The main task of the rebalancer is to consult the assignment policy associated with the database to get a list of documents (URIs) that do not “belong to” this forest and then push them out to the right forests. The deletion of documents from the rebalancing forest and the insertion of them into the right forests happens in the same transaction. All fragments with the same URI are handled by the same transaction. Each transaction moves a batch of documents.
When rebalancing is enabled, you can configure the rebalancer throttle for a database. The rebalancer throttle works the same as the reindexer throttle in that it establishes the priority of system resources devoted to rebalancing. When the rebalancer throttle is set to 5 (the default), the rebalancer works aggressively, starting the next batch of rebalancing soon after finishing the previous batch. When set to 4, it waits longer between batches, when set to 3 it waits even longer, and so on until when it is set to 1, it waits the longest. The higher numbers give rebalancing a higher priority and uses the most system resources.