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Comparison of Projection Methods

Difficult to compare, since they make different assumptions:
  • index-only: needs an appropriate index
  • hash-based: needs buffers and good hash functions
  • sort-based: needs only buffers ⇒ use as default

Best case scenario for each (assuming n+1 in-memory buffers):

  • index-only:   bi + bOut   ≪   bR + bOut
  • hash-based:   bR + 2.bP + bOut
  • sort-based:   bR + bT + 2.bT.ceil(lognb0) + bT + bOut
We normally omit bOut, since each method produces the same result