File Processing : Buffer

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File Processing Buffer

• 2005, Spring
• Pusan National University
• Ki-Joune Li

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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

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Buffer Management Read
Get Data
Access Request
Read Request
If in main memory
MainMemory
If not in main memory
Disk
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Buffer Management Write
Access Request
Write Request
If in main memory
MainMemory
If not in main memory
Disk
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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 users query to predict
  future references

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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.