Creating large scale database servers

The BaBar experiment at the Stanford Linear Accelerator Center (SLAC) is designed to perform a high precision investigation of the decays of B-meson produced from electron-positron interactions. The experiment, started in May 1999, will generate approximately 300 TB/year of data for 10 years. All of the data will reside in objectivity databases (object oriented databases), accessible via the Advanced Multi-threaded Server (AMS). To date, over 70 TB of data have been placed in Objectivity/DB, making it one of the largest databases in the world. Providing access to such a large quantity of data through a database server is a daunting task. A full-scale testbed environment had to be developed to tune various software parameters and a fundamental change had to occur in the AMS architecture to allow it to scale past several hundred terabytes of data. Additionally, several protocol extensions had to be implemented to provide practical access to large quantities of data. The paper describes the design of the database and the changes that we needed to make in the AMS for scalability reasons and how the lessons we learned would be applicable to virtually any kind of database server seeking to operate in the Petabyte region.