Early Scheduling in Parallel State Machine Replication.

State machine replication, a classic approach to fault tolerance, requires replicas to execute operations deterministically. Deterministic execution is typically ensured by having replicas execute operations serially in the same total order. Two classes of techniques have extended state machine replication to execute operations concurrently: late scheduling and early scheduling. With late scheduling, operations are scheduled for execution after they are ordered across replicas. With early scheduling, part of the scheduling decisions are made before requests are ordered; after requests are ordered, their scheduling must respect these restrictions. This paper generalizes early scheduling techniques. We propose an automated mechanism to schedule operations on worker threads at replicas, integrate our contributions to a popular state machine replication framework, and experimentally compare the resulting system to late scheduling.