Five-minute I/O rules (five-minute rule)

I paid attention to this five-minute rule when I was investigating "> SSD last year. Today I found another revision of this article (to commemorate Jim Gray). I can briefly introduce this topic, it is helpful for architects to measure I/O capabilities, evaluate the cache, and select hardware.

In 1987, Jim Gray and Gianfranco putzolu published the "five-minute rule". In short, if a record is frequently accessed, it should be stored in the memory, otherwise, you should try again on the hard disk as needed. This critical point is five minutes. It looks like an empirical rule. In fact, the five-minute evaluation criteria are determined based on the input cost and the hardware development level at that time, the cost of keeping 1 kb in the memory is equivalent to the overhead of storing data of the same size in the hard disk for 400 seconds (nearly five minutes ). This rule was reviewed around 1997 and confirmed that the five-minute rule is still effective (hard disk and memory are not actually a qualitative leap ), this review is about the potential impact of "> SSD" new hardware.

With the advent of the flash era, the five-minute rule is divided into two parts: "> SSD is used as a slow memory (Extended buffer pool) or as a fast hard disk (Extended disk. Small memory pages move between memory and flash memory compared to large memory pages move between flash memory and disk. 20 years after this rule was first proposed, in the Flash era, the 5-minute rule is still valid, but applicable to larger memory pages (applicable to 64 kB pages, the changes in the page size reflect the development of computer hardware technology, as well as bandwidth and latency ).

Depending on the data structure and characteristics, for file systems, the operating system tends to use "> SSD as the Instantaneous Memory (cache. For databases, "> SSD is used as consistent storage.

This is a very important article.Article(So it is recommended to read the original article). The description of the Database Section is particularly interesting (for "> dB also has five minutes ). The length is limited.

 

Note:

Author:Fenng |URL:Http://www.dbanotes.net/arch/five-minute_rule.html