Using Permuted States and Validated Simulation to Analyze Conflict Rates in Optimistic Replication

An-I Andy Wang, Geoff Kuenning, Peter Reiher
2007 Simulation (San Diego, Calif.)  
Optimistic replication provides high data availability in the presence of network outages. Although widely deployed, this relaxed consistency model introduces concurrent updates, whose behavior is poorly understood due to the vast state space. This paper introduces the notion of permuted states to eliminate system states that are redundant and unreachable, which can constitute the majority of states (4069 out of 4096 for four replicas). With the aid of permuted states, we are for the first time
more » ... able to construct analytical models beyond the two-replica case. By examining the analysis for 2 to 4 replicas, we can demystify the process of forming identical conflicts-the most common conflict type at high replication factors. Additionally, we have automated and optimized the generation of permuted states, which allows us to explore higher replication factors (up to 10 replicas) using hybrid techniques. It also allows us to validate our results with existing simulations based on actual replication mechanisms, which previously were analytically validated with only one pair of replicas. Finally, we have discovered that update locality and bimodal access patterns are the primary factors contributing to the formation of identical conflicts. case of improper concurrent modifications or conflicts. Common applications of optimistic replication include document sharing, banking and reservation systems. Coda [1], Lotus Notes [2], Ficus [3], Oracle 7 [4], Bayou [5], Ingres, Microsoft Briefcase, and the Concurrent Version System are well-known research and commercial systems that use optimistic replication. Although widely deployed, this relaxed consistency model introduces conflicts, whose behavior is not well understood. Empirical and simulation experience has shown evidence that conflicts occur infrequently at the level of aggregate statistics [3, 6, 7] . However, a theoretical result in the database literature suggests that the proliferation of conflicts will prevent optimistic replication from scaling
doi:10.1177/0037549707085073 fatcat:ph6xspcnkngglbhqgs5mhkwdu4