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10 Cards in this Set
- Front
- Back
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Program calls on buffer manager when it needs block from disk
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The requesting program is given the address of the block in main memory, if it is already present in the buffer.
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Program calls on buffer manager when it needs block from disk
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If the block is not in the buffer, the buffer manager allocates space in the buffer for the block, replacing (throwing out) some other blocks, if necessary to make space for new blocks.
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Program calls on buffer manager when it needs block from disk
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The block that is thrown out is written back to the disk only if it was modified since the most recent time that it was written to/fetched from the disk.
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Program calls on buffer manager when it needs block from disk
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Once space is allocated in the buffer, the buffer manager reads in the block from the disk to the buffer, and passes the address of the block in the main memory to the requesting program.
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LRU strategy
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Most operating systems replace the block least recently used
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LRU
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Use past reference of block as a predictor of future references
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Pinned block:
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memory block that is not allowed to be written back to disk
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Toss immediate strategy:
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frees the space occupied by a block as soon as the final record (tuple) of that block has been processed.
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Most recently used strategy
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system must pin the block currently being processed. After the final tuple of that block has been processed, the block is unpinned, and it becomes the most recently used block.
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LRU can be a bad strategy
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for certain access patterns involving repeated sequential scans of data files
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