Measuring and optimizing a system for persistent database sessions

High availability for both data and applications is rapidly becoming a business requirement. While database systems support recovery, providing high database availability, applications may still lose work because of server outages. When a server crashes, any volatile state associated with the application's database session is lost and the application may require an operator-assisted restart. This exposes server failures to end-users and always degrades application availability. Our Phoenix/ODBC system supports persistent database sessions that can survive a database crash without the application being aware of the outage, except for possible timing considerations. This improves application availability and eliminates the application programming needed to cope with database crashes. Phoenix/ODBC requires no changes to the database system, data access routines or applications. Hence, it can be deployed in any application that uses ODBC to access a database. Further, our generic approach can be exploited for a variety of data access protocols. In this paper, we describe the design of Phoenix/ODBC and introduce an extension to optimize the response time and to reduce overhead for OLTP workloads. We present a performance evaluation using the TPC-C and TPC-H benchmarks that demonstrate Phoenix/ODBC's extra overhead is modest.