<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
the	O
five-minute	B-General_Concept
rule	I-General_Concept
is	O
a	O
rule	O
of	O
thumb	O
for	O
deciding	O
whether	O
a	O
data	O
item	O
should	O
be	O
kept	O
in	O
memory	B-Architecture
,	O
or	O
stored	B-Device
on	I-Device
disk	I-Device
and	O
read	O
back	O
into	O
memory	B-Architecture
when	O
required	O
.	O
</s>
<s>
It	O
was	O
first	O
formulated	O
by	O
Jim	O
Gray	O
and	O
Gianfranco	O
Putzolu	O
in	O
1985	O
,	O
and	O
then	O
subsequently	O
revised	O
in	O
1997	O
and	O
2007	O
to	O
reflect	O
changes	O
in	O
the	O
relative	O
cost	O
and	O
performance	O
of	O
memory	B-Architecture
and	O
persistent	O
storage	O
.	O
</s>
<s>
The	O
rule	O
is	O
as	O
follows:The	O
5-minute	O
random	O
rule	O
:	O
cache	O
randomly	O
accessed	O
disk	B-Device
pages	O
that	O
are	O
re-used	O
every	O
5	O
minutes	O
or	O
less	O
.	O
</s>
<s>
Gray	O
also	O
issued	O
a	O
counterpart	O
one-minute	O
rule	O
for	O
sequential	B-General_Concept
access	I-General_Concept
:	O
</s>
<s>
The	O
1-minute	O
rule	O
:	O
cache	O
sequentially	O
accessed	O
disk	B-Device
pages	O
that	O
are	O
re-used	O
every	O
1	O
minute	O
or	O
less	O
.	O
</s>
<s>
Although	O
the	O
5-minute	O
rule	O
was	O
invented	O
in	O
the	O
realm	O
of	O
databases	O
,	O
it	O
has	O
also	O
been	O
applied	O
elsewhere	O
,	O
for	O
example	O
,	O
in	O
Network	B-Protocol
File	I-Protocol
System	I-Protocol
cache	O
capacity	O
planning	O
.	O
</s>
<s>
Applying	O
it	O
to	O
2007	O
data	O
yields	O
approximately	O
a	O
90-minutes	O
interval	O
for	O
magnetic-disk-to-DRAM	O
caching	O
,	O
15	O
minutes	O
for	O
SSD-to-DRAM	O
caching	O
and	O
2	O
hours	O
for	O
disk-to-SSD	O
caching	O
.	O
</s>
<s>
The	O
disk-to-DRAM	O
interval	O
was	O
thus	O
a	O
bit	O
short	O
of	O
what	O
Gray	O
and	O
Putzolu	O
anticipated	O
in	O
1987	O
as	O
the	O
"	O
five-hour	O
rule	O
"	O
was	O
going	O
to	O
be	O
in	O
2007	O
for	O
RAM	B-Architecture
and	O
disks	B-Device
.	O
</s>
<s>
Regarding	O
disk-to-SSD	O
caching	O
in	O
2010	O
,	O
the	O
same	O
source	O
reported	O
that	O
"	O
A	O
250KB	O
page	O
break	O
even	O
with	O
SLC	O
was	O
five	O
minutes	O
,	O
but	O
five	O
hours	O
with	O
a	O
4KB	O
page	O
size	O
.	O
</s>
<s>
In	O
2000	O
,	O
Gray	O
and	O
Shenoy	O
applied	O
a	O
similar	O
calculation	O
for	O
web	B-Protocol
page	I-Protocol
caching	I-Protocol
and	O
concluded	O
that	O
a	O
browser	O
should	O
"	O
cache	O
web	O
pages	O
if	O
there	O
is	O
any	O
chance	O
they	O
will	O
be	O
re-referenced	O
within	O
their	O
lifetime.	O
"	O
</s>
