State maintenance and its impact on the performability of multi-tiered Internet services

In this paper, we evaluate the performance, availability, and combined performability of four soft state maintenance strategies in two multitier Internet services, an online book store and an auction service. To take soft state and service latency into account, we propose an extension of our previous quantification methodology, and novel availability and performability metrics. Our results demonstrate that storing the soft state in a database can achieve better performability than storing it in main memory, even when the state is efficiently replicated. Strategies that offload the handling of soft state from the database increase the load on other tiers and, consequently, increase the impact of faults in these tiers on service availability. Based on these results, we conclude that service designers need to provision the cluster and balance the load with availability and cost, as well as performance, in mind.