Consistent Freshness-Aware Caching for Multi-Object Requests

Abstract

Dynamic websites rely on caching and clustering to achieve high performance and scalability. While queries benefit from middle-tier caching, updates introduce a distributed cache consistency problem. One promising approach to solving this problem is Freshness-Aware Caching (FAC): FAC tracks the freshness of cached data and allows clients to explicitly trade freshness of data for response times. The original protocol was limited to single-object lookups and could only handle complex requests if all requested objects had been loaded into the cache at the same time. In this paper we describe the Multi-Object Freshness-Aware Caching (MOFAC) algorithm, an extension of FAC that provides a consistent snapshot of multiple cached objects even if they are loaded and updated at different points of time. This is done by keeping track of their group valid interval, as introduced and defined in this paper. We have implemented MOFAC in the JBoss Java EE container so that it can provide freshness and consistency guarantees for cached Java beans. Our evaluation shows that those consistency guarantees come with a reasonable overhead and that MOFAC can provide significantly better read performance than cache invalidation in the case of concurrent updates and reads for multi-object requests.