Information Technology Reference
In-Depth Information
Algorithm 1. PrefixSpan-Prefetching (PSP)
Input
: Current access
o
c
, the trace library
L
, factor
k
and
d
.
Output
: Prefetching list
S
, where
2
≤
length S
( )
≤ +
k
1
.
1 As an initial sequence, let
S
=< >
;
o
c
2 let
L
'=
.
L
'
is a copy of
L
and will prevent the latter from any modifies
during the algorithm;
3 let
last
L
=
{ }
. The set last will contain all possible postfix items in the
prefetching list;
4
while
length S
o
c
( )
≤ +1
do
5
for
each
S
k
i
Î '
,
do
6
if
∀
L
P P
∈
last
⇒ ∈
P
S
i
(
)
then
7 select
P
x
Î
last
where
first S P
i
(
,
)
is the minimal;
x
8 supposing
first S P
(
,
)
=
, trim the first
n
items
n
i
x
of
S
i
;
9
else
10 delete
S
i
in
L
'
11
end
12
end
13
if
S
=< >
then
14 scan
L
'
once, find all possible items
P
, where
(
o
c
P
∈
S
)
∧
(
S
∈
L
')
∧
first S P
(
,
)
≤
d
, and <
P
> has the maximum support in
L
'
;
i
i
i
15
else
16 scan
L
'
once, find all possible items
P
, where
∀
S S
(
∈ ⇒ ∃
L
'
P P
(
∈
S
∧
first S P
(
,
)
≤
d
))
;
i
i
i
i
17
end
18 let
last
= ϕ
;
19
for
each possible items
P
in steps 13-17,
do
20 let
S
= + < >
;
21 let
last
S
P
=
last
∪
{ }
;
P
22
end
23
if
last
= ϕ
then
24 terminate the algorithm;
25
end
26
end
PERFORMANCE EVALUATION
a high-speed wide-area network. Some PCs are
idle and have free memory resources, whereas
servers are usually busy for tasks with mass
non-consequence data accesses (such as a web
server or DBMS), whose local physical memory
is intended to be utilized as much as possible. A
Simulation Methodology
Our application scenario is composed of abundant
PCs and several server stations loosely coupled in
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