In a replica set, upon step down from being the primary, any running operation that could not have been created in the new state should be aborted. I think that currently we just wait until we hit the closed socket that sent the operation. While ideally we wouldn't bother running the operation since it will fail anyway in the best case and should not be run in the worst. We should give some consideration to whether the operation is a read or write. Eg, an indexBuild on the primary should be aborted if it has not been replicated to the secondaries prior to step down.