setMaxMergesAndThreads
Expert: directly set the maximum number of merge threads and simultaneous merges allowed.
Parameters
maxMergeCount
the max # simultaneous merges that are allowed. If a merge is necessary yet we already have this many threads running, the incoming thread (that is calling add/updateDocument) will block until a merge thread has completed. Note that we will only run the smallest maxThreadCount merges at a time.
maxThreadCount
the max # simultaneous merge threads that should be running at once. This must be <= maxMergeCount