MTCache: transparent mid-tier database caching in SQL server

Many applications today run in a multitier environment with browser-based clients, midtier (application) servers and a backend database server. Midtier database caching attempts to improve system throughput and scalability by offloading part of the database workload to intermediate database servers that partially replicate data from the backend server. The fact that some queries are offloaded to an intermediate server should be completely transparent to applications - one of the key distinctions between caching and replication. MTCache is a prototype midtier database caching solution for SQL server that achieves this transparency. It builds on SQL server's support for materialized views, distributed queries and replication. We describe MTCache and report experimental results on the TPC-W benchmark. The experiments show that a significant part of the query workload can be offloaded to cache servers, resulting in greatly improved scale-out on the read-dominated workloads of the benchmark. Replication overhead was small with an average replication delay of less than two seconds.