Storage Access - Storage Access 1. Each file is partitioned...

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Storage Access 1. Each file is partitioned into fixed-length storage units, called blocks , which are the units of both storage allocation and data transfer. 2. It is desirable to keep as many blocks as possible in main memory. Usually, we cannot keep all blocks in main memory, so we need to manage the allocation of available main memory space. 3. We need to use disk storage for the database, and to transfer blocks of data between main memory and disk. We also want to minimize the number of such transfers, as they are time-consuming. 4. The buffer is the part of main memory available for storage of copies of disk blocks. Buffer manager Buffer replacement policies Buffer manager 1. The subsystem responsible for the allocation of buffer space is called the buffer manager . o The buffer manager handles all requests for blocks of the database. o If the block is already in main memory, the address in main memory is given to the requester. o If not, the buffer manager must read the block in from disk (possibly displacing some other block if the buffer is full) and then pass the address in main memory to the requester. 2. The buffer manager must use some sophisticated techniques in order to provide good service: o Replacement Strategy -- When there is no room left in the buffer, some
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This note was uploaded on 10/25/2010 for the course CMPN SEM4 taught by Professor Thakur during the Spring '07 term at University of Mumbai.

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Storage Access - Storage Access 1. Each file is partitioned...

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