<s>
mod_perl	O
is	O
an	O
optional	O
module	B-Language
for	O
the	O
Apache	B-Application
HTTP	I-Application
server	I-Application
.	O
</s>
<s>
It	O
embeds	O
a	O
Perl	B-Language
interpreter	I-Language
into	O
the	O
Apache	B-Application
server	I-Application
.	O
</s>
<s>
In	O
addition	O
to	O
allowing	O
Apache	B-Application
modules	B-Language
to	O
be	O
written	O
in	O
the	O
Perl	B-Language
programming	I-Language
language	I-Language
,	O
it	O
allows	O
the	O
Apache	B-Application
web	I-Application
server	I-Application
to	O
be	O
dynamically	O
configured	O
by	O
Perl	B-Language
programs	O
.	O
</s>
<s>
However	O
,	O
its	O
most	O
common	O
use	O
is	O
so	O
that	O
dynamic	O
content	O
produced	O
by	O
Perl	B-Language
scripts	B-Language
can	O
be	O
served	O
in	O
response	O
to	O
incoming	O
requests	O
,	O
without	O
the	O
significant	O
overhead	O
of	O
re-launching	O
the	O
Perl	B-Language
interpreter	I-Language
for	O
each	O
request	O
.	O
</s>
<s>
Slash	B-Protocol
,	O
which	O
runs	O
the	O
web	O
site	O
Slashdot	O
,	O
is	O
written	O
using	O
mod_perl	O
.	O
</s>
<s>
Early	O
versions	O
of	O
PHP	B-Application
were	O
implemented	O
in	O
Perl	B-Language
using	O
mod_perl	O
.	O
</s>
<s>
mod_perl	O
can	O
emulate	O
a	O
Common	B-Language
Gateway	I-Language
Interface	I-Language
(	O
CGI	O
)	O
environment	O
,	O
so	O
that	O
existing	O
Perl	B-Language
CGI	I-Language
scripts	B-Language
can	O
benefit	O
from	O
the	O
performance	O
boost	O
without	O
having	O
to	O
be	O
re-written	O
.	O
</s>
<s>
Unlike	O
CGI	O
(	O
and	O
most	O
other	O
web	O
application	O
environments	O
)	O
,	O
mod_perl	O
provides	O
complete	O
access	O
to	O
the	O
Apache	B-Application
API	B-Application
,	O
allowing	O
programmers	B-Application
to	O
write	O
handlers	O
for	O
all	O
phases	O
in	O
the	O
Apache	B-Application
request	O
cycle	O
,	O
manipulate	O
Apache	B-Application
's	O
internal	O
tables	O
and	O
state	O
mechanisms	O
,	O
share	O
data	O
between	O
Apache	B-Application
processes	B-Operating_System
or	O
threads	B-Operating_System
,	O
alter	O
or	O
extend	O
the	O
Apache	B-Application
configuration	B-Protocol
file	I-Protocol
parser	B-Language
,	O
and	O
add	O
Perl	B-Language
code	O
to	O
the	O
configuration	B-Protocol
file	I-Protocol
itself	O
,	O
among	O
other	O
things	O
.	O
</s>
