Experience with Rules-Based Programming for Distributed, Concurrent, Fault-Tolerant Code

This paper describes how a rules-based approach allowed us to solve a broad class of challenging distributed system problems in the RAMCloud storage system. In the rules-based approach, behavior is described with small sections of code that trigger independently based on system state; this provides a clean separation between the deterministic and nondeterministic parts of an algorithm. To simplify the implementation of rules-based modules, we developed a task abstraction for information hiding and complexity management, pools for grouping tasks and minimizing the cost of rule evaluation, and a polling-based asynchronous RPC system. The rules-based approach is a special case of an event-based state machine, but it encourages a cleaner factoring of code.