Recovery System Dbms

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17. Recovery System in DBMS - Presentation Transcript 1. Chapter 17: Recovery System * Failure Classification * Storage Structure * Recovery and Atomicity * Log-Based Recovery * Shadow Paging * Recovery With Concurrent Transactions * Buffer Management * Failure with Loss of Nonvolatile Storage * Advanced Recovery Techniques * ARIES Recovery Algorithm * Remote Backup Systems 2. Failure Classification * Transaction failure : * Logical errors : transaction cannot complete due to some internal error condition * System errors : the database system must terminate an active transaction due to an error condition (e.g., deadlock) *…show more content…
* Buffer blocks are the blocks residing temporarily in main memory. * Block movements between disk and main memory are initiated through the following two operations: * input ( B ) transfers the physical block B to main memory. * output ( B ) transfers the buffer block B to the disk, and replaces the appropriate physical block there. * Each transaction T i has its private work-area in which local copies of all data items accessed and updated by it are kept. * T i 's local copy of a data item X is called x i . * We assume, for simplicity, that each data item fits in, and is stored inside, a single block. 8. Data Access (Cont.) * Transaction transfers data items between system buffer blocks and its private work-area using the following operations : * read ( X ) assigns the value of data item X to the local variable x i . * write ( X ) assigns the value of local variable x i to data item { X } in the buffer block. * both these commands may necessitate the issue of an input (B X ) instruction before the assignment, if the block B X in which X resides is not already in memory. * Transactions * Perform read ( X ) while accessing X for the first time; * All subsequent accesses are to the local copy. * After last access, transaction executes write ( X ). * output ( B X ) need not immediately follow write ( X ).
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