In computer science

Computer science

Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

, the five-minute rule is a rule of thumb

Rule of thumb

A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination...

 for deciding whether a data item should be kept in memory

Random-access memory

Random access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...

, or stored on disk

Disk storage

Disk storage or disc storage is a general category of storage mechanisms, in which data are digitally recorded by various electronic, magnetic, optical, or mechanical methods on a surface layer deposited of one or more planar, round and rotating disks...

 and read back into memory when required. It was first formulated by Jim Gray and G. F. Putzolu in 1985, and then subsequently revised in 1997 and 2007 to reflect changes in the relative cost and performance of memory and persistent storage.

The rule is as follows:

The 5-minute random rule: cache randomly accessed disk pages that are re-used every 5 minutes.

External links

• Page Size and the Five-Minute Rule
• Jim Gray's entry under the "People" pages at Microsoft Research
• Jim Gray's website at Microsoft Research
• [ftp://ftp.research.microsoft.com/pub/tr/tr-99-100.pdf Rules of Thumb in Data Engineering] (Jim Gray, Prashant Shenoy) revised 2000 edition of the Five-Minute Rule and others