Many e-Business applications today are being developed and deployed on multi-tier environments involving browser-based clients, web application servers and backend databases. The dynamic nature of these applications necessitates generating web pages on-demand, making middle-tier database caching an effective approach to achieve high scalability and performance [3]. In the DBCache project, we are incorporating a database cache feature in DB2 UDB by modifying the engine code and leveraging existing federated database functionality. This allows us to take advantage of DB2's sophisticated distributed query processing power for database caching. As a result, the user queries can be executed at either the local database cache or the remote backend server, or more importantly, the query can be partitioned and then distributed to both databases for cost optimum execution.DBCache also includes a cache initialization component that takes a backend database schema and SQL queries in the workload, and generates a middle-tier database schema for the cache. We have implemented an initial prototype of the system that supports table level caching. As DB2's functionality is extended, we will be able to support subtable level caching, XML data caching and caching of execution results of web services.

Distributed shared memory (DSM) allows multicomputer systems with no physically shared memory to be programmed using a shared memory paradigm. However, as the number of nodes in a system increases the probability of a failure that can corrupt the DSM increases. This paper presents a fault-tolerant DSM (FTDSM) algorithm that can tolerate single node failures. Each page in the DSM is assigned a snooper that keeps a backup copy of the page and can take over if the page owner fails. The snooper is dynamic because the responsibility for snooping a page can migrate front node to node. The FTDSM presented is an improvement over other FTDSMs because it is scalable, is based on the efficient dynamic distributed manager (DDM) DSM algorithm, does not require the repair of a failed processor to access the DSM, and does not query all nodes to rebuild the state of the DSM. It is shown that any single node failure can be tolerated because either the owner or the snooper of a page can always be found.>