Data Mgmt Lab_Part_54 - 160 Chapter 16 (c) Isolation...

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Unformatted text preview: 160 Chapter 16 (c) Isolation ensures that a transaction can run independently, without consider- ing any side effects that other concurrently running transactions might have. When a database interleaves transaction actions for performance reasons, the database protects each transaction from the effects of other transactions. (d) Durability defines the persistence of committed data: once a transaction commits, the data should persist in the database even if the system crashes before the data is written to non-volatile storage. (e) A schedule is a series of (possibly overlapping) transactions. (f) A blind write is when a transaction writes to an object without ever reading the object. (g) A dirty read occurs when a transaction reads a database object that has been modified by another not-yet-committed transaction. (h) An unrepeatable read occurs when a transaction is unable to read the same object value more than once, even though the transaction has not modified the value. Suppose a transaction T2 changes the value of an object A that has been read by a transaction T1 while T1 is still in progress. If T1 tries to read the value of A again, it will get a different result, even though it has not modified A. (i) A serializable schedule over a set S of transactions is a schedule whose effect on any consistent database instance is identical to that of some complete serial schedule over the set of committed transactions in S. (j) A recoverable schedule is one in which a transaction can commit only after all other transactions whose changes it has read have committed....
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This note was uploaded on 01/17/2012 for the course EGN 4302 taught by Professor Dr.vishak during the Fall '12 term at University of Central Florida.

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Data Mgmt Lab_Part_54 - 160 Chapter 16 (c) Isolation...

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