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2.2.17. Query optimisation

  • External sorting
    • Stems from large disk (2y), small memory (1y)
    • Sort-merge strategy
      • Sort runs (small sets of total data file)
      • Then merge runs back together
    • Used in
      • SELECT, to accelerate selection (by index)
      • PROJECT, to eliminate duplicates
      • JOIN, UNION and INTERSECTION
    ‹ 2.2.16b. Query optimisation implementationup2.3. B-trees ›
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