General External Merge Sort

• To sort a file with N pages using B buffer pages:

  • Pass 0: use B buffer pages. Produce sorted runs of B pages each.
  • Pass 2, …, etc.: merge B-1 runs.

B Main memory buffers

INPUT 1

INPUT B-1

OUTPUT

Disk

Disk

INPUT 2

. . .

. . .

. . .

• More than 3 buffer pages. How can we utilize them?

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