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File Processing : Buffer

File Processing : Buffer. 2011, Spring Pusan National University Ki-Joune Li. Buffer. Buffer Temporary memory to transfer a chunk of data 1 buffer : multiple blocks Page A piece of buffer (main memory) corresponding with block Page Replacement when buffer is full. Get Data.

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File Processing : Buffer

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  1. File Processing : Buffer 2011, Spring Pusan National University Ki-Joune Li

  2. Buffer • Buffer • Temporary memory to transfer a chunk of data • 1 buffer : multiple blocks • Page • A piece of buffer (main memory) corresponding with block • Page Replacement when buffer is full

  3. Get Data Load on main memoryand Replacement Access to Disk Buffer Management : Read Get Data Access Request Read Request If in main memory MainMemory If not in main memory Disk

  4. Write Data Write Data on Disk Write Data Load on main memoryand Replacement Access to Disk Buffer Management : Write Access Request Write Request If in main memory MainMemory If not in main memory Disk

  5. Buffer Manager : Replacement Policy • LRU • Replace the block least recently used • Most operating system and buffer management • Idea behind LRU – use past pattern of block references as a predictor of future references • Prediction of future reference • Queries have well-defined access patterns (such as sequential scans), and a database system can use the information in a user’s query to predict future references

  6. Buffer Manager : Replacement Policy • Pinned block : • memory block that is not allowed to be written back to disk. • Toss-immediate strategy : • frees the space occupied by a block as soon as the final tuple of that block has been processed • Most recently used (MRU) strategy : • 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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