ch10-2 - Chapter 10 Introduction to Transaction Management...

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Chapter 10 Introduction to Transaction Management Example 10.5 A transaction T consisting of operations Read(x) Read(y) x x+y Write(x) Commit = {R(x), R(y), W(x), C} h = {(R(x),W(x)), (R(y),W(x)), (W(x),C), (R(x),C), (R(y),C)} A partial order can be represented by a DAG (Directed Acyclic Graph) whose vertices are the operations and edges are ordering. Example 10.5 R(x) W(x) C R(y) Note no order exists between R(x) and R(y) A transaction can be simplified by using its relative order of operations, e.g. the above T can be written as T={R(x), R(y),W(x),C} 7
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Chapter 10 Introduction to Transaction Management 10.2 PROPETIES OF TRANSACTIONS 10.2.1 Atomicity “All-or-nothing” principle. 10.2.2 Consistency The property to be guaranteed by concurrency control . Four levels of consistency can be defined on the basis of dirty data concept. Dirty data – the data value that have been changed by a transaction prior to its commitment. Consistency degree 3 1. A transaction T does not overwrite dirty data of other transactions. 2. A transaction T does not commit any
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This note was uploaded on 12/23/2009 for the course DBST 663 taught by Professor Tba during the Spring '09 term at MD University College.

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ch10-2 - Chapter 10 Introduction to Transaction Management...

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