The Five-Minute Rule 20 Years Later: and How Flash Memory Changes the Rules

  • Authors:
  • Goetz Graefe

  • Affiliations:
  • Hewlett-Packard Laboratories

  • Venue:
  • Queue - Enterprise Flash Storage
  • Year:
  • 2008

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Abstract

The old rule continues to evolve, while flash memory adds two new rules. In 1987, Jim Gray and Gianfranco Putzolu published their now-famous five-minute rule for trading off memory and I/O capacity. Their calculation compares the cost of holding a record (or page) permanently in memory with the cost of performing disk I/O each time the record (or page) is accessed, using appropriate fractions of prices for RAM chips and disk drives. The name of their rule refers to the break-even interval between accesses. If a record (or page) is accessed more often, it should be kept in memory; otherwise, it should remain on disk and read when needed.