We have introduced a few new parameters for controlling replication behavior and performance:

Server parameter:

• replWriterThreadCount; default is 16, range is 1 to 256 inclusive. Server parameter settable at startup but not on a running server. Number of threads used to apply replicated operations in parallel.

Replica Set Config parameters:

Top level parameters:

• configsvr: true
  Indicates this replica set is to be used for Sharding Config Servers; default is "false".
  protocolVersion: 1
  Selects the new election protocol that allows faster failover; default is 1 for new replica sets

Parameters in "settings" subobject:

• electionTimeoutMillis: The time limit for detecting when a replica set's primary is unreachable. Raise this value for slower failover, but less sensitivity to primary node or network slowness or spottiness. Lower this value for faster failover, but more sensitivity to primary node or network slowness or spottiness. This value only applies if protocolVersion is set to 1. Default is 10,000 (10 seconds).
• heartbeatIntervalMillis: How often heartbeats are delivered. Internal use only.