practice
Doi: 10.1145/1538788.1538805
was about equal to the (fractional)
price of a disk drive required to access
such a record every 400 seconds, which
they rounded to five minutes. The
break-even interval is about inversely
proportional to the record size. Gray and
Putzolu reported one hour for 100-byte
records and two minutes for 4KB pages.
BY Goe Tz GRAefe
The five-minute rule was reviewed
and renewed 10 years later. 14 Lots of
prices and performance parameters
had changed (for example, the price of
RAM had tumbled from $5,000 to $15
per megabyte). Nonetheless, the break-
Minute Rule even interval for 4KB pages was still
around five minutes. The first goal of
this article is to review the five-minute
rule after another 10 years.
20 Years Later
Of course, both previous articles
acknowledged that prices and
performance vary among technologies and devices at any point in time
(and how flash Memory (RAM for mainframes versus minicomputers, SCSI versus IDE disks, and
so on). Interested readers are invited to
Changes the Rules) reevaluate the appropriate formulas
for their environments and equipment.
The values used here (in Table 1) are
meant to be typical for 2007 technologies rather than universally accurate.
In addition to quantitative
changes in prices and performance,
qualitative changes already under
way will affect the software and
hardware architectures of servers
and, in particular, database systems.
Database software will change
radically with the advent of new
technologies: virtualization with
hardware and software support, as well
as higher utilization goals for physical
machines; many-core processors and
transactional memory supported both
in programming environments and
hardware; 20 deployment in containers
housing thousands of processors and
many terabytes of data; 17 and flash
memory that fills the gap between
traditional RAM and traditional
rotating disks.
Flash memory falls between
traditional RAM and persistent mass
storage based on rotating disks in
terms of acquisition cost, access
Article development led by
queue.acm.org
Revisiting Gray and Putzolu’s
famous rule in the age of Flash.
The five-
in 1987, JiM
Gray and Gianfranco Putzolu published
their now-famous five-minute rule15 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 fractional prices of 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
be read when needed.
Based on then-current prices and performance
characteristics of Tandem equipment, Gray and
Putzolu found the price of RAM to hold a 1KB record
