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Unswizzling an address (replacing the memory address with a database address)

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Slideshow:

Problem 1: "unswizzle" all references in block when block is written back to disk

We cannot write the data block containg memory address to disk
Problem 1: "unswizzle" all references in block when block is written back to disk

We must replace all (virtual) memory address by its database address
Problem 1: "unswizzle" all references in block when block is written back to disk

$64,000 question: HOW ? (to translate a virtual memory address to a database address)
Naive solution: brute force search

Search for the memory address in the Translation Table and replace it with the corresponding database address
Improved solution: reverse hash table

Hash the memory address in a new "reverse" Translation Table for fast lookup
Example of the improved solution: reverse hash table

Hash the memory address in a new "reverse" Translation Table for fast lookup
Maintaining the reverse hash table

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• Solving problem 1: Unswizzling a virtual memory address
  • Recall problem 1:

    When the block in memory is written back to disk: We must first perform an inverse swizzling operation on all swizzled pointers in the block before writing the block to disk !!!

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• Brute force (naive) solution: search...
  • Naive solution:

    Use a brute force search in the Translation Table: When the virtual address is found, we replace it with the corresponding database address

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• Speedier solution: use an inverse table
  • Improved solution:

    We use another hash table to speed up the search using the virtual memory address: Virtual Memory Address ----> Translation Table index Example usage:

    Note:

    When we insert an entry k in the translation (hash) table: We must also insert the corresponding entry in the invert-translation hash table