<s>
Cassandra	B-Application
is	O
a	O
free	B-License
and	I-License
open-source	I-License
,	O
distributed	B-Operating_System
,	O
wide-column	B-Application
store	I-Application
,	O
NoSQL	B-General_Concept
database	O
management	O
system	O
designed	O
to	O
handle	O
large	O
amounts	O
of	O
data	O
across	O
many	O
commodity	B-Device
servers	I-Device
,	O
providing	O
high	O
availability	O
with	O
no	B-Architecture
single	I-Architecture
point	I-Architecture
of	I-Architecture
failure	I-Architecture
.	O
</s>
<s>
Cassandra	B-Application
offers	O
support	O
for	O
clusters	B-Architecture
spanning	O
multiple	O
datacenters	O
,	O
with	O
asynchronous	O
masterless	O
replication	B-Architecture
allowing	O
low	O
latency	O
operations	O
for	O
all	O
clients	O
.	O
</s>
<s>
Cassandra	B-Application
was	O
designed	O
to	O
implement	O
a	O
combination	O
of	O
Amazon	B-Application
's	I-Application
Dynamo	I-Application
distributed	B-Operating_System
storage	O
and	O
replication	B-Architecture
techniques	O
combined	O
with	O
Google	O
's	O
Bigtable	B-Application
data	O
and	O
storage	O
engine	O
model	O
.	O
</s>
<s>
Avinash	O
Lakshman	O
,	O
one	O
of	O
the	O
authors	O
of	O
Amazon	B-Application
's	I-Application
Dynamo	I-Application
,	O
and	O
Prashant	O
Malik	O
initially	O
developed	O
Cassandra	B-Application
at	O
Facebook	B-Application
to	O
power	O
the	B-Application
Facebook	I-Application
inbox	O
search	O
feature	O
.	O
</s>
<s>
Facebook	B-Application
released	O
Cassandra	B-Application
as	O
an	O
open-source	O
project	O
on	O
Google	B-Protocol
code	I-Protocol
in	O
July	O
2008	O
.	O
</s>
<s>
In	O
March	O
2009	O
,	O
it	O
became	O
an	O
Apache	B-Application
Incubator	I-Application
project	O
.	O
</s>
<s>
Facebook	B-Application
developers	O
named	O
their	O
database	O
after	O
the	O
Trojan	O
mythological	O
prophet	O
Cassandra	B-Application
,	O
with	O
classical	O
allusions	O
to	O
a	O
curse	O
on	O
an	O
oracle	B-General_Concept
.	O
</s>
<s>
3.1	O
through	O
3.10	O
releases	O
were	O
monthly	O
releases	O
using	O
a	O
tick-tock-like	O
release	O
model	O
,	O
with	O
even-numbered	O
releases	O
providing	O
both	O
new	O
features	O
and	O
bug	O
fixes	O
while	O
odd-numbered	O
releases	O
will	O
include	O
bug	O
fixes	O
only	O
.	O
</s>
<s>
3.11	O
released	O
June	O
23	O
,	O
2017	O
as	O
a	O
stable	O
3.11	O
release	O
series	O
and	O
bug	O
fix	O
from	O
the	O
last	O
tick-tock	B-Device
feature	O
release	O
.	O
</s>
<s>
There	O
is	O
no	B-Architecture
single	I-Architecture
point	I-Architecture
of	I-Architecture
failure	I-Architecture
.	O
</s>
<s>
Data	O
is	O
distributed	B-Operating_System
across	O
the	O
cluster	O
(	O
so	O
each	O
node	O
contains	O
different	O
data	O
)	O
,	O
but	O
there	O
is	O
no	O
master	O
as	O
every	O
node	O
can	O
service	O
any	O
request	O
.	O
</s>
<s>
Replication	B-Architecture
strategies	O
are	O
configurable	O
.	O
</s>
<s>
Cassandra	B-Application
is	O
designed	O
as	O
a	O
distributed	B-Operating_System
system	O
,	O
for	O
deployment	O
of	O
large	O
numbers	O
of	O
nodes	O
across	O
multiple	O
data	O
centers	O
.	O
</s>
<s>
Key	O
features	O
of	O
Cassandra	B-Application
’s	O
distributed	B-Operating_System
architecture	O
are	O
specifically	O
tailored	O
for	O
multiple-data	O
center	O
deployment	O
,	O
for	O
redundancy	O
,	O
for	O
failover	O
and	O
disaster	O
recovery	O
.	O
</s>
<s>
Data	O
is	O
automatically	O
replicated	O
to	O
multiple	O
nodes	O
for	O
fault-tolerance	B-General_Concept
.	O
</s>
<s>
Replication	B-Architecture
across	O
multiple	O
data	O
centers	O
is	O
supported	O
.	O
</s>
<s>
Cassandra	B-Application
is	O
typically	O
classified	O
as	O
an	O
AP	B-Operating_System
system	I-Operating_System
,	O
meaning	O
that	O
availability	O
and	O
partition	O
tolerance	O
are	O
generally	O
considered	O
to	O
be	O
more	O
important	O
than	O
consistency	B-General_Concept
in	O
Cassandra	B-Application
,	O
Writes	O
and	O
reads	O
offer	O
a	O
tunable	O
level	O
of	O
consistency	B-General_Concept
,	O
all	O
the	O
way	O
from	O
"	O
writes	O
never	O
fail	O
"	O
to	O
"	O
block	O
for	O
all	O
replicas	B-Architecture
to	O
be	O
readable	O
"	O
,	O
with	O
the	O
quorum	B-General_Concept
level	I-General_Concept
in	O
the	O
middle	O
.	O
</s>
<s>
Cassandra	B-Application
has	O
Hadoop	B-Application
integration	O
,	O
with	O
MapReduce	B-Operating_System
support	O
.	O
</s>
<s>
There	O
is	O
support	O
also	O
for	O
Apache	B-Language
Pig	I-Language
and	O
Apache	B-General_Concept
Hive	I-General_Concept
.	O
</s>
<s>
Cassandra	B-Application
introduced	O
the	O
Cassandra	B-Application
Query	B-Language
Language	O
(	O
CQL	O
)	O
.	O
</s>
<s>
CQL	O
is	O
a	O
simple	O
interface	O
for	O
accessing	O
Cassandra	B-Application
,	O
as	O
an	O
alternative	O
to	O
the	O
traditional	O
Structured	B-Language
Query	I-Language
Language	I-Language
(	O
SQL	B-Language
)	O
.	O
</s>
<s>
Cassandra	B-Application
manages	O
eventual	O
consistency	B-General_Concept
of	O
reads	O
,	O
upserts	O
and	O
deletes	O
through	O
Tombstones	O
.	O
</s>
<s>
Cassandra	B-Application
introduced	O
the	O
Cassandra	B-Application
Query	B-Language
Language	O
(	O
CQL	O
)	O
.	O
</s>
<s>
CQL	O
is	O
a	O
simple	O
interface	O
for	O
accessing	O
Cassandra	B-Application
,	O
as	O
an	O
alternative	O
to	O
the	O
traditional	O
Structured	B-Language
Query	I-Language
Language	I-Language
(	O
SQL	B-Language
)	O
.	O
</s>
<s>
Language	O
drivers	O
are	O
available	O
for	O
Java	B-Language
(	O
JDBC	O
)	O
,	O
Python	O
(	O
DBAPI2	O
)	O
,	O
Node.JS	O
(	O
Datastax	O
)	O
,	O
Go	O
(	O
gocql	O
)	O
and	O
C++	B-Language
.	O
</s>
<s>
The	O
keyspace	O
in	O
Cassandra	B-Application
is	O
a	O
namespace	O
that	O
defines	O
data	B-Architecture
replication	I-Architecture
across	O
nodes	O
.	O
</s>
<s>
Therefore	O
,	O
replication	B-Architecture
is	O
defined	O
at	O
the	O
keyspace	O
level	O
.	O
</s>
<s>
Below	O
an	O
example	O
of	O
keyspace	O
creation	O
,	O
including	O
a	O
column	B-Application
family	I-Application
in	O
CQL	O
3.0	O
:	O
</s>
<s>
Up	O
to	O
Cassandra	B-Application
1.0	O
,	O
Cassandra	B-Application
was	O
not	O
row-level	O
consistent	O
,	O
meaning	O
that	O
inserts	O
and	O
updates	O
into	O
the	O
table	O
that	O
affect	O
the	O
same	O
row	O
that	O
are	O
processed	O
at	O
approximately	O
the	O
same	O
time	O
may	O
affect	O
the	O
non-key	O
columns	O
in	O
inconsistent	O
ways	O
.	O
</s>
<s>
Cassandra	B-Application
1.1	O
solved	O
this	O
issue	B-Application
by	O
introducing	O
row-level	O
isolation	B-General_Concept
.	O
</s>
<s>
Cassandra	B-Application
is	O
not	O
supported	O
on	O
Windows	O
as	O
of	O
version	O
4	O
,	O
see	O
issue	B-Application
CASSANDRA-16171	O
.	O
</s>
<s>
Cassandra	B-Application
is	O
wide	B-Application
column	I-Application
store	I-Application
,	O
and	O
,	O
as	O
such	O
,	O
essentially	O
a	O
hybrid	O
between	O
a	O
key-value	O
and	O
a	O
tabular	O
database	O
management	O
system	O
.	O
</s>
<s>
Its	O
data	O
model	O
is	O
a	O
partitioned	O
row	O
store	O
with	O
tunable	O
consistency	B-General_Concept
.	O
</s>
<s>
Rows	O
are	O
organized	O
into	O
tables	B-Application
;	O
the	O
first	O
component	O
of	O
a	O
table	O
's	O
primary	O
key	O
is	O
the	O
partition	O
key	O
;	O
within	O
a	O
partition	O
,	O
rows	O
are	O
clustered	O
by	O
the	O
remaining	O
columns	O
of	O
the	O
key	O
.	O
</s>
<s>
Tables	B-Application
may	O
be	O
created	O
,	O
dropped	O
,	O
and	O
altered	O
at	O
run-time	O
without	O
blocking	O
updates	O
and	O
queries	B-Language
.	O
</s>
<s>
Cassandra	B-Application
cannot	O
do	O
joins	B-Language
or	O
subqueries	B-Language
.	O
</s>
<s>
Rather	O
,	O
Cassandra	B-Application
emphasizes	O
denormalization	O
through	O
features	O
like	O
collections	O
.	O
</s>
<s>
A	O
column	B-Application
family	I-Application
(	O
called	O
"	O
table	O
"	O
since	O
CQL	O
3	O
)	O
resembles	O
a	O
table	O
in	O
an	O
RDBMS	O
(	O
Relational	O
Database	O
Management	O
System	O
)	O
.	O
</s>
<s>
Column	B-Application
families	I-Application
contain	O
rows	O
and	O
columns	O
.	O
</s>
<s>
Unlike	O
a	O
table	O
in	O
an	O
RDBMS	O
,	O
different	O
rows	O
in	O
the	O
same	O
column	B-Application
family	I-Application
do	O
not	O
have	O
to	O
share	O
the	O
same	O
set	O
of	O
columns	O
,	O
and	O
a	O
column	O
may	O
be	O
added	O
to	O
one	O
or	O
multiple	O
rows	O
at	O
any	O
time	O
.	O
</s>
<s>
Each	O
key	O
in	O
Cassandra	B-Application
corresponds	O
to	O
a	O
value	O
which	O
is	O
an	O
object	O
.	O
</s>
<s>
Each	O
key	O
has	O
values	O
as	O
columns	O
,	O
and	O
columns	O
are	O
grouped	O
together	O
into	O
sets	O
called	O
column	B-Application
families	I-Application
.	O
</s>
<s>
These	O
column	B-Application
families	I-Application
could	O
be	O
considered	O
then	O
as	O
tables	B-Application
.	O
</s>
<s>
A	O
table	O
in	O
Cassandra	B-Application
is	O
a	O
distributed	B-Operating_System
multi	O
dimensional	O
map	O
indexed	O
by	O
a	O
key	O
.	O
</s>
<s>
Furthermore	O
,	O
applications	O
can	O
specify	O
the	O
sort	O
order	O
of	O
columns	O
within	O
a	O
Super	O
Column	O
or	O
Simple	O
Column	B-Application
family	I-Application
.	O
</s>
<s>
Cassandra	B-Application
is	O
a	O
Java-based	O
system	O
that	O
can	O
be	O
managed	O
and	O
monitored	O
via	O
Java	B-Language
Management	I-Language
Extensions	I-Language
(	O
JMX	O
)	O
.	O
</s>
<s>
The	O
JMX-compliant	O
nodetool	O
utility	O
,	O
for	O
instance	O
,	O
can	O
be	O
used	O
to	O
manage	O
a	O
Cassandra	B-Application
cluster	O
(	O
adding	O
nodes	O
to	O
a	O
ring	O
,	O
draining	O
nodes	O
,	O
decommissioning	O
nodes	O
,	O
and	O
so	O
on	O
)	O
.	O
</s>
<s>
Nodetool	O
also	O
offers	O
a	O
number	O
of	O
commands	O
to	O
return	O
Cassandra	B-Application
metrics	O
pertaining	O
to	O
disk	O
usage	O
,	O
latency	O
,	O
compaction	O
,	O
garbage	O
collection	O
,	O
and	O
more	O
.	O
</s>
<s>
Since	O
Cassandra	B-Application
2.0.2	O
in	O
2013	O
,	O
measures	O
of	O
several	O
metrics	O
are	O
produced	O
via	O
the	O
Dropwizard	O
metrics	O
framework	O
,	O
and	O
may	O
be	O
queried	O
via	O
JMX	O
using	O
tools	O
such	O
as	O
JConsole	B-Language
or	O
passed	O
to	O
external	O
monitoring	O
systems	O
via	O
Dropwizard-compatible	O
reporter	O
plugins	O
.	O
</s>
