# The Key to Performance:Turn 10 Instructions Into 1

- ## When Data is Always in Memory...

  - SQL Optimization is Unambiguous
  - Data Copying is Eliminated
  - Data is Referenced via Memory Addresses

- ## When Data is Mostly on Disk

  - SQL Optimization is Biased Toward I/O
  - Data is Copied for Every Access
  - Data is Referenced via Disk Addresses, which Require Translation into Memory Buffers

- ## On Average, Copying, Indirection, and an I/O Bias Use 10 Times More Instructions Than Necessary

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