<s>
ApacheBench	B-Application
(	O
ab	O
is	O
the	O
real	O
program	B-Application
file	I-Application
name	O
)	O
is	O
a	O
single-threaded	B-Operating_System
command	O
line	O
computer	B-Application
program	I-Application
used	O
for	O
benchmarking	O
(	O
measuring	O
the	O
performance	O
of	O
)	O
HTTP	B-Application
web	I-Application
servers	I-Application
.	O
</s>
<s>
Originally	O
it	O
was	O
used	O
to	O
test	O
the	O
Apache	B-Application
HTTP	I-Application
Server	I-Application
but	O
it	O
is	O
generic	O
enough	O
to	O
test	O
any	O
web	B-Application
server	I-Application
supporting	O
HTTP/1.0	B-Protocol
or	O
HTTP/1.1	B-Protocol
protocol	O
versions	O
.	O
</s>
<s>
The	O
ab	O
tool	O
is	O
written	O
in	O
C	B-Language
and	O
it	O
comes	O
bundled	O
with	O
the	O
standard	O
Apache	B-Application
source	O
distribution	O
,	O
and	O
like	O
the	O
Apache	B-Application
web	I-Application
server	I-Application
itself	O
,	O
is	O
free	O
,	O
open	B-Application
source	I-Application
software	I-Application
and	O
distributed	O
under	O
the	O
terms	O
of	O
the	O
Apache	B-Application
License	I-Application
.	O
</s>
<s>
The	O
original	O
program	B-Application
was	O
named	O
zb	O
"	O
ZeusBench	O
V1.0	O
"	O
and	O
it	O
was	O
written	O
by	O
Adam	O
Twiss	O
(	O
Zeus	O
Technology	O
)	O
,	O
in	O
1996	O
,	O
in	O
order	O
to	O
test	O
performance	O
of	O
Zeus	B-Protocol
Web	I-Protocol
Server	I-Protocol
.	O
</s>
<s>
Soon	O
later	O
Twiss	O
licensed	O
(	O
donated	O
)	O
that	O
program	B-Application
to	O
the	O
Apache	B-Application
Group	O
so	O
that	O
the	O
derived	O
program	B-Application
was	O
renamed	O
ab	O
"	O
ApacheBench	B-Application
"	O
.	O
</s>
<s>
Since	O
1997	O
,	O
1998	O
ab	O
has	O
been	O
further	O
developed	O
and	O
maintained	O
,	O
as	O
a	O
support	O
program	B-Application
included	O
in	O
Apache	B-Application
HTTP	I-Application
server	I-Application
,	O
from	O
version	O
1.0	O
(	O
1997	O
,	O
1998	O
)	O
to	O
version	O
2.3	O
(	O
2021	O
)	O
and	O
later	O
.	O
</s>
<s>
Excerpt	O
from	O
comments	O
about	O
copyright	O
attributions	O
found	O
in	O
source	O
code	O
of	O
ab	O
program	B-Application
.	O
</s>
<s>
This	O
will	O
execute	O
10000	O
HTTP	B-Protocol
GET	O
requests	O
,	O
processing	O
up	O
to	O
10	O
requests	O
concurrently	O
,	O
to	O
the	O
specified	O
URL	O
,	O
in	O
this	O
example	O
,	O
http://localhost/index.html	O
which	O
requires	O
that	O
a	O
web	B-Application
server	I-Application
is	O
running	O
on	O
port	O
80	O
of	O
the	O
same	O
computer	O
where	O
ab	O
is	O
run	O
.	O
</s>
<s>
Note	O
that	O
ApacheBench	B-Application
will	O
only	O
use	O
one	O
operating	B-General_Concept
system	I-General_Concept
thread	B-Operating_System
regardless	O
of	O
the	O
concurrency	B-Operating_System
level	I-Operating_System
(	O
specified	O
by	O
the	O
parameter	O
)	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
especially	O
when	O
benchmarking	O
high-capacity	O
servers	B-Application
,	O
a	O
single	O
instance	O
of	O
ApacheBench	B-Application
can	O
itself	O
be	O
a	O
bottleneck	O
.	O
</s>
<s>
When	O
using	O
ApacheBench	B-Application
on	O
hardware	O
with	O
multiple	O
processor	O
cores	O
,	O
additional	O
instances	O
of	O
ApacheBench	B-Application
may	O
be	O
used	O
in	O
parallel	O
to	O
more	O
fully	O
saturate	O
the	O
target	O
URL	O
.	O
</s>
<s>
The	O
ApacheBench	B-Application
User	B-Protocol
Agent	I-Protocol
string	O
is	O
where	O
MAJOR	O
and	O
MINOR	O
represent	O
the	O
major	O
and	O
minor	O
version	O
numbers	O
of	O
the	O
program	B-Application
.	O
</s>
<s>
It	O
is	O
usually	O
not	O
correctly	O
categorised	O
by	O
web	B-Application
server	I-Application
log	O
analysers	O
such	O
as	O
Webalizer	B-Application
or	O
AWStats	B-Protocol
,	O
so	O
running	O
ApacheBench	B-Application
with	O
a	O
great	O
number	O
of	O
requests	O
may	O
skew	O
the	O
results	O
of	O
the	O
reports	O
generated	O
by	O
these	O
programs	O
.	O
</s>
