<s>
Distributed	B-Operating_System
web	I-Operating_System
crawling	I-Operating_System
is	O
a	O
distributed	B-Architecture
computing	I-Architecture
technique	O
whereby	O
Internet	B-Application
search	I-Application
engines	I-Application
employ	O
many	O
computers	O
to	O
index	B-Application
the	O
Internet	O
via	O
web	B-Application
crawling	I-Application
.	O
</s>
<s>
The	O
central	O
server	O
may	O
become	O
the	O
bottleneck	O
,	O
so	O
most	O
of	O
the	O
workload	O
must	O
be	O
transferred	O
to	O
the	O
distributed	B-Operating_System
crawling	I-Operating_System
processes	O
for	O
large	O
crawls	O
.	O
</s>
<s>
A	O
small	O
crawler	O
configuration	O
,	O
in	O
which	O
there	O
is	O
a	O
central	O
DNS	B-Protocol
resolver	O
and	O
central	O
queues	O
per	O
Web	O
site	O
,	O
and	O
distributed	O
downloaders	O
.	O
</s>
<s>
A	O
large	O
crawler	O
configuration	O
,	O
in	O
which	O
the	O
DNS	B-Protocol
resolver	O
and	O
the	O
queues	O
are	O
also	O
distributed	O
.	O
</s>
<s>
For	O
static	O
assignment	O
,	O
a	O
hashing	O
function	O
can	O
be	O
used	O
to	O
transform	O
URLs	O
(	O
or	O
,	O
even	O
better	O
,	O
complete	O
website	O
names	O
)	O
into	O
a	O
number	O
that	O
corresponds	O
to	O
the	O
index	B-Application
of	O
the	O
corresponding	O
crawling	O
process	O
.	O
</s>
<s>
As	O
of	O
2003	O
,	O
most	O
modern	O
commercial	O
search	B-Application
engines	I-Application
use	O
this	O
technique	O
.	O
</s>
<s>
Google	B-Application
and	O
Yahoo	B-Application
use	O
thousands	O
of	O
individual	O
computers	O
to	O
crawl	O
the	O
Web	O
.	O
</s>
<s>
LookSmart	O
is	O
the	O
largest	O
search	B-Application
engine	I-Application
to	O
use	O
this	O
technique	O
,	O
which	O
powers	O
its	O
Grub	B-Application
distributed	I-Application
web-crawling	I-Application
project	I-Application
.	O
</s>
<s>
Wikia	O
(	O
now	O
known	O
as	O
Fandom	O
)	O
acquired	O
Grub	B-Application
from	O
LookSmart	O
in	O
2007	O
.	O
</s>
<s>
According	O
to	O
the	O
FAQ	O
about	O
Nutch	B-Language
,	O
an	O
open-source	B-Application
search	I-Application
engine	I-Application
website	O
,	O
the	O
savings	O
in	O
bandwidth	O
by	O
distributed	B-Operating_System
web	I-Operating_System
crawling	I-Operating_System
are	O
not	O
significant	O
,	O
since	O
"	O
A	O
successful	O
search	B-Application
engine	I-Application
requires	O
more	O
bandwidth	O
to	O
upload	O
query	O
result	O
pages	O
than	O
its	O
crawler	O
needs	O
to	O
download	O
pages	O
...	O
"	O
.	O
</s>
