Distributed_One_Copy_Serializability_with_Snap

Distributed_One_Copy_Serializability_with_Snap -...

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Unformatted text preview: Distributed OneCopy Serializability with Snapshot Isolation Aspen Olmsted CSCE Fall Background Isolation Isolation is a property that defines howwhen the changes made by one operation become visible to other concurrent operations Concurrency phenomena There are three different read phenomena when Transaction reads data that Transaction might have changed and one update phenomena when two transactions update the same date item Lost Updates Dirty Reads Nonrepeatable reads Phantom reads Concurrency Control Ensure that correct results for concurrent operations are generated Pessimistic concurrency control Optimistic concurrency control Pessimistic Concurrency Control Block an operation of a transaction if it may cause violation of the rules until the possibility of violation disappears Optimistic Concurrency Control Assumes that multiple transactions can complete without affecting each other and that therefore transactions can proceed without locking the data resources that they affect Before committing each transaction verifies that no other transaction has modified its data If the check reveals conflicting modifications the committing transaction rolls back Lost Update WriteWrite Conflict A lost update occurs when a transaction is allowed to overwrite data from a row that has been modified by another running transaction Lost Update Example Transaction Update Course Set students = Where id = CSCE Update Semester Set Start = = where id = SP Commit Transaction Update Course Set students = Where id = CSCE Commit Dirty Reads A dirty read occurs when a transaction is allowed to read data from a row that has been modified by another running transaction and not yet committed Dirty Read Example Transaction Select students from Course where id = CSCE Transaction Update Course Set students = Where id = CSCE Rollback Nonrepeatable reads A nonrepeatable read occurs when during the course of a transaction a row is retrieved twice and the values within the row differ between reads Nonrepeatable Read Example Transaction Select students from Course where id = CSCE Select students from Course where id = CSCE Transaction Update Course Set students = Where id = CSCE Commit Phantom reads...
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This note was uploaded on 12/13/2011 for the course CSCE 824 taught by Professor Staff during the Fall '11 term at South Carolina.

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Distributed_One_Copy_Serializability_with_Snap -...

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