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Identifying blocks/records in memory

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Slideshow:

Review: block stored in computer memory


Review: block stored in computer memory


The fact that disk blocks can be stored in 2 difference places (on disk and in memory) will create 2 problems (ambiguity !!) that we must solve...
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• Accessing disk block by computer applications
  • Important fact:

    A block/record must be transfered to the main memory in order to perform read/update operations on data in the block

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• Identifying a block/record in memory
  • Fact:

    Data stored in the computer memory are located at a specific memory address

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  • Identifying a block/record when it is in memory:

    Use a (virtual) memory address (paging)

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• Virtual Memory Address: address used to identify block/record in main memory

  • Locating data blocks/records stored in computer memory:

    Because: Each data item stored in (main) memory is identified by its virtual memory address Therefore: When a block/record is in memory, we must use its virtual address to identify (= locate) the block/record:

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  • Important conclusions:

    We need a mechanism to find out: whether a data block is in memory (or not)          We need a mechanism to translate (map): Database address ---> Memory address in order to locate the (disk) block or record in memory !!! (This topic will be discussed later)