11 - Distributed databases

11 - Distributed databases - Session 11: Database System...

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Session 11: Database System Architectures Centralized Systems Client--Server Systems Parallel Systems Distributed Systems Network Types Distributed Databases CS585 – Fall 2010 – Farid Parvini
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Centralized Systems Run on a single computer system and do not interact with other computer systems. General-purpose computer system: one to a few CPUs and a number of device controllers that are connected through a common bus that provides access to shared memory. Single-user system (e.g., personal computer or workstation): desk-top unit, single user, usually has only one CPU and one or two hard disks; the OS may support only one user. Multi-user system: more disks, more memory, multiple CPUs, and a multi-user OS. Serve a large number of users who are connected to the system vie terminals. Often called server systems.
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A Centralized Computer System
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Client-Server Systems Server systems satisfy requests generated at m client systems, whose general structure is shown below:
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Client-Server Systems (Cont.) Database functionality can be divided into: Back-end : manages access structures, query evaluation and optimization, concurrency control and recovery. Front-end : consists of tools such as forms , report-writers , and graphical user interface facilities. The interface between the front-end and the back-end is through SQL or through an application program interface.
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Client-Server Systems (Cont.) Advantages of replacing mainframes with networks of workstations or personal computers connected to back-end server machines: better functionality for the cost flexibility in locating resources and expanding facilities better user interfaces easier maintenance Server systems can be broadly categorized into two kinds: transaction servers which are widely used in relational database systems, and data servers , used in object-oriented database systems
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Transaction Servers Also called query server systems or SQL server systems; clients send requests to the server system where the transactions are executed, and results are shipped back to the client. Requests specified in SQL, and communicated to the server through a remote procedure call (RPC) mechanism. Transactional RPC allows many RPC calls to collectively form a transaction. e.g Open Database Connectivity (ODBC) is a application program interface standard from Microsoft for connecting to a server, sending SQL requests, and receiving results. JDBC standard similar to ODBC, for Java
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Transaction Server Process Structure A typical transaction server consists of multiple processes accessing data in shared memory. Server processes
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11 - Distributed databases - Session 11: Database System...

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