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Session 19.pptx - Session 19 2017-18 KL University The...

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Session 19 © 2017-18 KL University – The contents of this presentation are an intellectual and copyrighted property of KL University. ALL RIGHTS RESERVED
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Agenda: Transaction processing issues ACID Properties Recoverability © 2017-18 KL University – The contents of this presentation are an intellectual and copyrighted property of KL University. ALL RIGHTS RESERVED
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1 Introduction to Transaction Processing (1) Single-User System: At most one user at a time can use the system. Multiuser System : Many users can access the system concurrently. Concurrency Interleaved processing : concurrent execution of processes is interleaved in a single CPU Parallel processing : processes are concurrently executed in multiple CPUs. © 2017-18 KL University – The contents of this presentation are an intellectual and copyrighted property of KL University. ALL RIGHTS RESERVED
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Introduction to Transaction Processing (2) A Transaction: logical unit of database processing that includes one or more access operations (read -retrieval, write - insert or update, delete). 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. Transaction boundaries : Begin and End transaction. An application program may contain several transactions separated by the Begin and End transaction boundaries. © 2017-18 KL University – The contents of this presentation are an intellectual and copyrighted property of KL University. ALL RIGHTS RESERVED
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Introduction to Transaction Processing (3) SIMPLE MODEL OF A DATABASE (for purposes of discussing transactions): A database - collection of named data items Granularity of data - a field, a record , or a whole disk block (Concepts are independent of granularity) Basic operations are read and write read_item(X) : Reads a database item named X into a program variable. To simplify our notation, we assume that the program variable is also named X. write_item(X) : Writes the value of program variable X into the database item named X. © 2017-18 KL University – The contents of this presentation are an intellectual and copyrighted property of KL University. ALL RIGHTS RESERVED
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Introduction to Transaction Processing (4) READ AND WRITE OPERATIONS: 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, although it may be a larger unit such as a record or even a whole block. read_item(X) command includes the following steps: 1. Find the address of the disk block that contains item X. 2. Copy that disk block into a buffer in main memory (if that disk block is not already in some main memory buffer).
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