Last update: Apr 1, 2000
Speaker: Victoria WhiteThe Sequential Access Model, or SAM, is the data access layer which being built for Run II data handling at D0. It requires the mass storage services of a separate Run II component, the ENSTORE mass storage system, also developed at Fermilab. SAM's goals are to provide a straightforward interface for users of both batch and interactive applications, to provide a robust and easily accessible database for locating and describing datasets, to archive descriptions of data analysis projects, to promote efficient use of computing and network resources, and to help optimize performance from the data storage and delivery system. Although it has been built with D0's requirements for Run II in mind, its design is not D0 specific.
A commercial RDBMS is used to maintain a carefully designed schema which includes event, file, processing and required physics information. The database chosen was ORACLE, since it was realized early on that a robust and mature product was essential to the longterm stability of the system. Also, the size of the database is anticipated to be several hundred GB, and many features in Oracle are useful in managing a repository of this magnitude. The schema has been designed to catalog event, file, various run and physics information. It allows tracking data through a wide variety of complex processing steps, and tracing lineage from detector or Monte Carlo files through analysis stages. Information crucial to many types of analysis, such as trigger, luminosity, and accelerator conditions are available through the system. SAM is a distributed system using a client-server architecture. The architecture includes multiple servers which inter-communicate among each other and to and from clients through CORBA interfaces. One of the principle servers manages all communication with the database, another manages data delivery to multiple clients on various processing platforms, and yet another server is responsible for storing data into the system. Additional servers collect information from the system at large, and provide other important functions. The servers are written in c++ and Python. Clients are written using c++, Python, and some web based GUI's employ Java.
The SAM system has been integrated with the Enstore, and D0 analysis systems, and is being used for testing and D0 Monte Carlo data management. Its feature list includes 1) data and data-description storage, 2) list-directed data delivery 3) command line interface to all functions, 4) Gui interface to applicable functions, 5)web-based database browsing tools, 6) disk cache and buffer management, and 6)system monitoring tools. The system is documented and being used by D0 physicists to perform simple analyses tasks. Several additional features are planed over the next 6 months, including a facility for extracting single events, additional error handling, and more support for remote site implementations.
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