<s>
A	O
server	B-Algorithm
hog	I-Algorithm
is	O
a	O
user	O
,	O
program	O
or	O
system	O
that	O
places	O
excessive	O
load	O
on	O
a	O
server	B-Application
such	O
that	O
the	O
server	B-Application
performance	O
as	O
experienced	O
by	O
other	O
clients	B-Protocol
is	O
degraded	O
,	O
or	O
such	O
that	O
the	O
server	B-Application
itself	O
is	O
so	O
heavily	O
loaded	O
that	O
it	O
fails	O
to	O
perform	O
routine	O
housekeeping	O
for	O
its	O
own	O
maintenance	O
.	O
</s>
<s>
In	O
the	O
early	O
years	O
of	O
time-sharing	B-General_Concept
computer	O
systems	O
in	O
the	O
1960s	O
it	O
was	O
common	O
for	O
a	O
single	O
institutional	O
mainframe	B-Architecture
to	O
control	O
many	O
interactive	O
terminals	O
.	O
</s>
<s>
In	O
such	O
an	O
environment	O
server	B-Application
lag	O
is	O
acutely	O
perceived	O
.	O
</s>
<s>
Furthermore	O
,	O
in	O
many	O
operating	O
environments	O
,	O
scarce	O
server	B-Application
resources	O
such	O
as	O
CPU-seconds	O
were	O
often	O
metered	O
and	O
charged	O
against	O
the	O
account	O
of	O
the	O
user	O
running	O
the	O
program	O
.	O
</s>
<s>
An	O
unintentional	O
server	B-Algorithm
hog	I-Algorithm
could	O
prove	O
extremely	O
costly	O
in	O
financial	O
terms	O
.	O
</s>
<s>
Server	B-Application
performance	O
has	O
many	O
dimensions	O
.	O
</s>
<s>
Any	O
subsystem	O
that	O
becomes	O
excessively	O
loaded	O
can	O
compromise	O
the	O
performance	O
of	O
other	O
clients	B-Protocol
contending	O
for	O
that	O
subsystem	O
.	O
</s>
<s>
At	O
the	O
software	O
level	O
,	O
contention	O
can	O
arise	O
for	O
buffers	B-General_Concept
,	O
queues	B-Device
,	O
spools	B-Device
,	O
or	O
page	B-General_Concept
tables	I-General_Concept
.	O
</s>
<s>
It	O
is	O
an	O
accepted	O
practice	O
that	O
servers	O
are	O
appropriately	O
sized	O
by	O
system	O
administrators	O
for	O
the	O
workload	O
(	O
or	O
mixture	O
of	O
workloads	O
)	O
expected	O
,	O
and	O
server	B-Application
performance	O
is	O
closely	O
monitored	O
to	O
establish	O
performance	O
baselines	O
.	O
</s>
<s>
The	O
server	B-Application
load	O
might	O
include	O
well	O
known	O
server	B-Algorithm
hogs	I-Algorithm
,	O
such	O
as	O
system	O
backup	O
.	O
</s>
<s>
These	O
tasks	O
are	O
generally	O
scheduled	O
for	O
time	O
periods	O
of	O
light	O
demand	O
,	O
such	O
as	O
in	O
the	O
very	O
early	O
hours	O
on	O
a	O
Sunday	O
morning	O
,	O
with	O
an	O
accepted	O
administrative	O
policy	O
to	O
discourage	O
or	O
prohibit	O
other	O
demands	O
on	O
the	O
server	B-Application
during	O
those	O
time	O
periods	O
.	O
</s>
<s>
More	O
often	O
,	O
the	O
term	O
server	B-Algorithm
hog	I-Algorithm
is	O
used	O
to	O
designate	O
an	O
unusual	O
load	O
condition	O
where	O
the	O
server	B-Application
performance	O
falls	O
short	O
of	O
the	O
culturally	O
accepted	O
baseline	O
.	O
</s>
<s>
A	O
common	O
scenario	O
in	O
the	O
early	O
years	O
of	O
computing	O
was	O
an	O
overload	O
condition	O
known	O
as	O
thrashing	B-General_Concept
where	O
the	O
aggregate	O
server	B-Application
performance	O
becomes	O
severely	O
degraded	O
,	O
such	O
as	O
when	O
two	O
departments	O
of	O
a	O
large	O
company	O
attempt	O
to	O
run	O
a	O
heavy	O
report	O
concurrently	O
on	O
the	O
same	O
mainframe	B-Architecture
.	O
</s>
<s>
In	O
such	O
a	O
situation	O
,	O
the	O
designation	O
of	O
the	O
server	B-Algorithm
hog	I-Algorithm
becomes	O
a	O
political	O
matter	O
of	O
pointing	O
fingers	O
,	O
as	O
the	O
termination	O
of	O
either	O
long-running	O
report	O
would	O
restore	O
the	O
server	B-Application
to	O
normal	O
performance	O
.	O
</s>
<s>
In	O
the	O
internet	O
era	O
,	O
the	O
nature	O
of	O
server	B-Application
loads	O
greatly	O
changed	O
,	O
as	O
the	O
clients	B-Protocol
became	O
increasingly	O
dispersed	O
geographically	O
,	O
and	O
often	O
increasingly	O
anonymous	O
,	O
as	O
for	O
example	O
,	O
any	O
member	O
of	O
the	O
public	O
with	O
internet	O
access	O
can	O
request	O
a	O
web	O
server	B-Application
in	O
any	O
part	O
of	O
the	O
world	O
to	O
deliver	O
a	O
web	O
page	O
.	O
</s>
<s>
In	O
this	O
context	O
,	O
a	O
server	B-Algorithm
hog	I-Algorithm
most	O
commonly	O
designates	O
a	O
malicious	O
server	B-Algorithm
hog	I-Algorithm
—	O
a	O
program	O
written	O
expressly	O
for	O
the	O
purpose	O
of	O
overloading	O
a	O
remote	O
server	B-Application
with	O
excessive	O
requests	O
or	O
excessively	O
difficult	O
requests	O
(	O
such	O
as	O
complex	O
search	O
)	O
.	O
</s>
<s>
Use	O
of	O
a	O
deliberate	O
server	B-Algorithm
hog	I-Algorithm
is	O
known	O
as	O
a	O
denial-of-service	O
attack	O
,	O
a	O
behaviour	O
exhibited	O
by	O
many	O
viruses	O
,	O
worms	O
and	O
trojan	O
horses	O
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
for	O
a	O
petulant	O
or	O
vindictive	O
computer	O
user	O
to	O
manually	O
overload	O
a	O
remote	O
server	B-Application
by	O
unleashing	O
a	O
crap	O
flood	O
.	O
</s>
<s>
A	O
special	O
case	O
is	O
that	O
of	O
a	O
run-away	O
bot	B-Protocol
,	O
a	O
program	O
that	O
was	O
designed	O
to	O
be	O
helpful	O
by	O
automating	O
a	O
drudgerous	O
task	O
,	O
but	O
due	O
to	O
poor	O
programming	O
or	O
poorly	O
understood	O
circumstances	O
,	O
goes	O
out	O
of	O
control	O
and	O
hammers	O
a	O
server	B-Application
unceasingly	O
at	O
a	O
high	O
rate	O
.	O
</s>
<s>
A	O
common	O
case	O
is	O
a	O
web	B-Application
spider	I-Application
which	O
accesses	O
too	O
many	O
pages	O
on	O
a	O
web	O
server	B-Application
too	O
quickly	O
at	O
the	O
expense	O
of	O
the	O
server	B-Application
's	O
intended	O
audience	O
.	O
</s>
