<s>
Apache	B-Language
Accumulo	I-Language
is	O
a	O
highly	O
scalable	O
sorted	O
,	O
distributed	O
key-value	O
store	O
based	O
on	O
Google	B-Application
's	I-Application
Bigtable	B-Application
.	O
</s>
<s>
It	O
is	O
a	O
system	O
built	O
on	O
top	O
of	O
Apache	B-Application
Hadoop	I-Application
,	O
Apache	B-Language
ZooKeeper	I-Language
,	O
and	O
Apache	B-Protocol
Thrift	I-Protocol
.	O
</s>
<s>
Written	O
in	O
Java	B-Language
,	O
Accumulo	B-Language
has	O
cell-level	O
access	O
labels	O
and	O
server-side	B-Language
programming	I-Language
mechanisms	O
.	O
</s>
<s>
According	O
to	O
DB-Engines	B-Application
ranking	I-Application
,	O
Accumulo	B-Language
is	O
the	O
third	O
most	O
popular	O
NoSQL	B-General_Concept
wide	B-Application
column	I-Application
store	I-Application
behind	O
Apache	B-Application
Cassandra	I-Application
and	O
HBase	B-Language
and	O
the	O
67th	O
most	O
popular	O
database	O
engine	O
of	O
any	O
type	O
(	O
complete	O
)	O
as	O
of	O
2018	O
.	O
</s>
<s>
Accumulo	B-Language
was	O
created	O
in	O
2008	O
by	O
the	O
US	O
National	O
Security	O
Agency	O
and	O
contributed	O
to	O
the	O
Apache	O
Foundation	O
as	O
an	O
incubator	O
project	O
in	O
September	O
2011	O
.	O
</s>
<s>
On	O
March	O
21	O
,	O
2012	O
,	O
Accumulo	B-Language
graduated	O
from	O
incubation	O
at	O
Apache	O
,	O
making	O
it	O
a	O
top-level	O
project	O
.	O
</s>
<s>
In	O
June	O
2012	O
,	O
the	O
US	O
Senate	O
Armed	O
Services	O
Committee	O
(	O
SASC	O
)	O
released	O
the	O
Draft	O
2012	O
Department	O
of	O
Defense	O
(	O
DoD	O
)	O
Authorization	O
Bill	O
,	O
which	O
included	O
references	O
to	O
Apache	B-Language
Accumulo	I-Language
.	O
</s>
<s>
In	O
the	O
draft	O
bill	O
SASC	O
required	O
DoD	O
to	O
evaluate	O
whether	O
Apache	B-Language
Accumulo	I-Language
could	O
achieve	O
commercial	O
viability	O
before	O
implementing	O
it	O
throughout	O
DoD	O
.	O
</s>
<s>
Specific	O
criteria	O
were	O
not	O
included	O
in	O
the	O
draft	O
language	O
,	O
but	O
the	O
establishment	O
of	O
commercial	O
entities	O
supporting	O
Apache	B-Language
Accumulo	I-Language
could	O
be	O
considered	O
a	O
success	O
factor	O
.	O
</s>
<s>
Apache	B-Language
Accumulo	I-Language
extends	O
the	O
Bigtable	B-Application
data	O
model	O
,	O
adding	O
a	O
new	O
element	O
to	O
the	O
key	O
called	O
.	O
</s>
<s>
In	O
addition	O
to	O
Cell-Level	O
Security	O
,	O
Apache	B-Language
Accumulo	I-Language
provides	O
a	O
server-side	B-Language
programming	I-Language
mechanism	O
called	O
Iterators	O
that	O
allows	O
users	O
to	O
perform	O
additional	O
processing	O
at	O
the	O
Tablet	O
Server	O
.	O
</s>
<s>
Apache	B-Language
Accumulo	I-Language
orders	O
entries	O
in	O
order	O
of	O
user	O
keys	O
,	O
and	O
exposes	O
an	O
iterator	O
over	O
a	O
key	O
range	O
.	O
</s>
<s>
This	O
allows	O
locality	O
of	O
reference	O
not	O
available	O
from	O
some	O
other	O
distributed	O
stores	O
(	O
including	O
Cassandra	B-Application
and	O
Voldemort	O
that	O
order	O
by	O
hash	O
of	O
the	O
user	O
key	O
)	O
.	O
</s>
