<s>
PowerDNS	B-Language
is	O
a	O
DNS	B-Protocol
server	I-Protocol
program	O
,	O
written	O
in	O
C++	B-Language
and	O
licensed	O
under	O
the	O
GPL	B-License
.	O
</s>
<s>
It	O
runs	O
on	O
most	O
Unix	B-Application
derivatives	O
.	O
</s>
<s>
PowerDNS	B-Language
features	O
a	O
large	O
number	O
of	O
different	O
backends	B-Architecture
ranging	O
from	O
simple	O
BIND	B-Protocol
style	O
zonefiles	O
to	O
relational	B-Application
databases	I-Application
and	O
load	O
balancing/failover	O
algorithms	O
.	O
</s>
<s>
A	O
DNS	B-Protocol
recursor	O
is	O
provided	O
as	O
a	O
separate	O
program	O
.	O
</s>
<s>
PowerDNS	B-Language
development	O
began	O
in	O
1999	O
and	O
was	O
originally	O
a	O
commercial	O
proprietary	O
product	O
.	O
</s>
<s>
In	O
November	O
2002	O
,	O
the	O
source	O
code	O
was	O
made	O
public	O
under	O
the	O
open-source	O
GPL	B-License
v2	O
license	O
.	O
</s>
<s>
PowerDNS	B-Language
Authoritative	O
Server	O
(	O
pdns_server	O
)	O
consists	O
of	O
a	O
single	O
core	O
,	O
and	O
multiple	O
dynamically	B-Library
loadable	I-Library
backends	B-Architecture
that	O
run	O
multi-threaded	B-Operating_System
.	O
</s>
<s>
The	O
core	O
handles	O
all	O
packet	O
processing	O
and	O
DNS	B-Protocol
intelligence	O
,	O
while	O
one	O
or	O
more	O
backends	B-Architecture
deliver	O
DNS	B-Protocol
records	O
using	O
arbitrary	O
storage	B-General_Concept
methods	I-General_Concept
.	O
</s>
<s>
Zone	B-Protocol
transfers	I-Protocol
and	O
update	O
notifications	O
are	O
supported	O
,	O
and	O
the	O
processes	O
can	O
run	O
unprivileged	O
and	O
chrooted	B-Application
.	O
</s>
<s>
Run-time	B-Library
control	O
is	O
available	O
through	O
the	O
pdns_control	O
command	O
,	O
which	O
allows	O
reloading	O
of	O
separate	O
zones	O
,	O
cache	O
purges	O
,	O
zone	O
notifications	O
and	O
dumps	O
statistics	O
in	O
Multi	B-Protocol
Router	I-Protocol
Traffic	I-Protocol
Grapher	I-Protocol
/	O
rrdtool	B-Language
format	O
.	O
</s>
<s>
Realtime	O
information	O
can	O
also	O
be	O
obtained	O
through	O
the	O
optional	O
built-in	O
web	B-Application
server	I-Application
.	O
</s>
<s>
There	O
are	O
many	O
independent	O
projects	O
to	O
create	O
management	O
interfaces	O
for	O
PowerDNS	B-Language
.	O
</s>
<s>
The	O
PowerDNS	B-Language
Authoritative	O
Server	O
supports	O
DNSSEC	B-Protocol
as	O
of	O
version	O
3.0	O
.	O
</s>
<s>
PowerDNS	B-Language
Recursor	O
(	O
pdns_recursor	O
)	O
is	O
a	O
resolving	O
DNS	B-Protocol
server	I-Protocol
,	O
that	O
runs	O
as	O
a	O
separate	O
process	O
.	O
</s>
<s>
This	O
part	O
of	O
PowerDNS	B-Language
uses	O
a	O
combination	O
of	O
native	O
threads	B-Operating_System
and	O
user-space	O
threads	B-Operating_System
,	O
through	O
the	O
use	O
of	O
Boost	B-Language
and	O
the	O
MTasker	O
library	O
,	O
which	O
is	O
a	O
simple	O
cooperative	O
multitasking	O
library	O
.	O
</s>
<s>
Support	O
for	O
DNSSEC	B-Protocol
validation	O
was	O
added	O
to	O
the	O
pdns_recursor	O
in	O
version	O
4.0	O
.	O
</s>
