Transintro - Transaction Processing Concepts Introduction...

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Transaction Processing Concepts
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Introduction to Transaction Processing b The concept of transaction provides a mechanism for describing logical units of a database Processing . b Transaction processing systems include large databases and hundreds of concurrent users executing database transactions s Examples of these systems are: – airline reservations – banking – credit card processing – supermarket checkout b These system requires high availability and fast response time for hundreds of concurrent users
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Introduction to Transaction Processing b Database system is classified according to the number of users who use the system concurrently. b Single-User System: At most one user at a time can use the system. b Multiuser System : Many users can access the system concurrently. b Concurrent database usage is possible with multiprogramming s Interleaved processing : Concurrent execution of processes is interleaved in a single CPU s Parallel processing : Processes are concurrently executed in multiple CPUs.
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Interleaved Versus Parallel Processing interleaved processing parallel processing t 1 t 2 t 1 t 2 CPU 1 CPU 2 A B A B CPU 1
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Introduction to Transaction Processing b A Transaction: L ogical unit of database processing that includes one or more access operations (read -retrieval, write - insert or update, delete). b A transaction (set of operations) may be stand-alone specified in a high level language like SQL submitted interactively, or may be embedded within a program. b Transaction boundaries : Begin and End transaction. b An application program may contain several transactions separated by the Begin and End transaction boundaries.
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Introduction to Transaction Processing b Basic operations are read and write s read_item(X) : Reads a database item named X into a program variable X. s write_item(X) : Writes the value of program variable X into the database item named X.
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Transaction Processing
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b Basic unit of data transfer from the disk to the computer main memory is one block . In general, a data item (what is read or written) will be the field of some record in the database b
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Transintro - Transaction Processing Concepts Introduction...

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