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Data Access(Cont.) Each transaction T;has its private work-area in which local copies of all data items accessed and updated by it are kept. Ti's local copy of a data item X is called xi. Transferring data items between system buffer blocks and its private work-area done by: read(X)assigns the value of data item X to the local variable xj. write(X)assigns the value of local variable xi to data item {X)in the buffer block. Note:output(B)need not immediately follow write(X).System can perform the output operation when it deems fit. Transactions Must perform read(X)before accessing X for the first time (subsequent reads can be from local copy) write(X)can be executed at any time before the transaction commits Database System Concepts-6th Edition 16.10 @Silberschatz,Korth and SudarshanDatabase System Concepts - 6 16.10 ©Silberschatz, Korth and Sudarshan th Edition Data Access (Cont.) Each transaction Ti has its private work-area in which local copies of all data items accessed and updated by it are kept. Ti 's local copy of a data item X is called xi . Transferring data items between system buffer blocks and its private work-area done by: read(X) assigns the value of data item X to the local variable xi . write(X) assigns the value of local variable xi to data item {X} in the buffer block. Note: output(BX) need not immediately follow write(X). System can perform the output operation when it deems fit. Transactions Must perform read(X) before accessing X for the first time (subsequent reads can be from local copy) write(X) can be executed at any time before the transaction commits
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