<s>
A	O
distributed	B-Language
SQL	I-Language
database	O
is	O
a	O
single	O
relational	B-Application
database	I-Application
which	O
replicates	O
data	O
across	O
multiple	O
servers	O
.	O
</s>
<s>
Distributed	B-Language
SQL	I-Language
databases	B-Application
are	O
strongly	O
consistent	O
and	O
most	O
support	O
consistency	O
across	O
racks	O
,	O
data	O
centers	O
,	O
and	O
wide	O
area	O
networks	O
including	O
cloud	O
availability	O
zones	O
and	O
cloud	O
geographic	O
zones	O
.	O
</s>
<s>
Distributed	B-Language
SQL	I-Language
databases	B-Application
typically	O
use	O
the	O
Paxos	B-Operating_System
or	O
Raft	B-Operating_System
algorithms	O
to	O
achieve	O
consensus	O
across	O
multiple	O
nodes	O
.	O
</s>
<s>
Sometimes	O
distributed	B-Language
SQL	I-Language
databases	B-Application
are	O
referred	O
to	O
as	O
NewSQL	B-General_Concept
but	O
NewSQL	B-General_Concept
is	O
a	O
more	O
inclusive	O
term	O
that	O
includes	O
databases	B-Application
that	O
are	O
not	O
distributed	B-Application
databases	I-Application
.	O
</s>
<s>
Google	B-Application
's	I-Application
Spanner	B-Operating_System
popularized	O
the	O
modern	O
distributed	B-Language
SQL	I-Language
database	O
concept	O
.	O
</s>
<s>
Google	B-Application
described	O
the	O
database	O
and	O
its	O
architecture	O
in	O
a	O
2012	O
whitepaper	O
called	O
"	O
Spanner	B-Operating_System
:	O
Google	B-Application
's	I-Application
Globally-Distributed	O
Database.	O
"	O
</s>
<s>
The	O
paper	O
described	O
Spanner	B-Operating_System
as	O
having	O
evolved	O
from	O
a	O
Big	O
Table-like	O
key	B-Application
value	I-Application
store	O
into	O
a	O
temporal	O
multi-version	O
database	O
where	O
data	O
is	O
stored	O
in	O
"	O
schematized	O
semi-relational	O
tables.	O
"	O
</s>
<s>
Spanner	B-Operating_System
uses	O
atomic	O
clocks	O
with	O
the	O
Paxos	B-Operating_System
algorithm	I-Operating_System
to	O
accomplish	O
consensus	O
with	O
regards	O
to	O
state	O
distributed	O
between	O
servers	O
.	O
</s>
<s>
In	O
2010	O
,	O
and	O
earlier	O
implementation	O
,	O
ClustrixDB	O
(	O
now	O
MariaDB	B-Application
Xpand	I-Application
)	O
moved	O
from	O
a	O
hardware	O
appliance	O
to	O
a	O
Paxos-based	O
software	O
database	O
and	O
was	O
later	O
acquired	O
by	O
MariaDB	B-Application
and	O
added	O
to	O
a	O
SaaS	B-Architecture
cloud	O
offering	O
called	O
SkySQL	B-Application
.	O
</s>
<s>
In	O
2015	O
,	O
two	O
Google	B-Application
engineers	O
left	O
the	O
company	O
to	O
create	O
Cockroach	B-Operating_System
DB	I-Operating_System
which	O
achieves	O
similar	O
results	O
using	O
the	O
Raft	B-Operating_System
algorithm	O
without	O
atomic	O
clocks	O
or	O
custom	O
hardware	O
.	O
</s>
<s>
Spanner	B-Operating_System
is	O
primarily	O
used	O
for	O
transactional	O
and	O
time-series	O
use	O
cases	O
.	O
</s>
<s>
However	O
,	O
Google	B-Application
furthered	O
this	O
research	O
with	O
a	O
follow	O
on	O
paper	O
about	O
Google	B-Operating_System
F1	I-Operating_System
which	O
it	O
describes	O
as	O
a	O
Hybrid	O
transactional/analytical	O
processing	O
database	O
built	O
on	O
Spanner	B-Operating_System
.	O
</s>
<s>
Distributed	B-Language
SQL	I-Language
databases	B-Application
have	O
the	O
following	O
general	O
characteristics	O
:	O
</s>
<s>
Following	O
the	O
CAP	B-Operating_System
Theorem	I-Operating_System
,	O
distributed	B-Language
SQL	I-Language
databases	B-Application
are	O
"	O
CP	O
"	O
or	O
consistent	O
and	O
partition-tolerant	O
.	O
</s>
<s>
All	O
distributed	B-Language
SQL	I-Language
implementations	O
require	O
some	O
kind	O
of	O
temporal	O
synchronization	O
to	O
guarantee	O
consistency	O
.	O
</s>
<s>
With	O
the	O
exception	O
of	O
Spanner	B-Operating_System
,	O
most	O
do	O
not	O
use	O
custom	O
hardware	O
to	O
provide	O
atomic	O
clocks	O
.	O
</s>
<s>
Spanner	B-Operating_System
is	O
able	O
to	O
synchronize	O
writes	O
with	O
temporal	O
guarantees	O
.	O
</s>
<s>
CockroachDB	B-Operating_System
,	O
YugabyteDB	B-Operating_System
and	O
others	O
have	O
at	O
times	O
referred	O
to	O
themselves	O
as	O
NewSQL	B-General_Concept
databases	B-Application
.	O
</s>
<s>
Some	O
of	O
the	O
NewSQL	B-General_Concept
databases	B-Application
like	O
Citus	O
and	O
Vitess	O
have	O
fundamentally	O
different	O
architectures	O
,	O
but	O
were	O
cited	O
as	O
examples	O
of	O
NewSQL	B-General_Concept
by	O
Matthew	O
Aslett	O
who	O
coined	O
the	O
term	O
.	O
</s>
<s>
In	O
essence	O
,	O
distributed	B-Language
SQL	I-Language
databases	B-Application
are	O
built	O
from	O
the	O
ground-up	O
and	O
NewSQL	B-General_Concept
databases	B-Application
include	O
replication	O
and	O
sharding	B-General_Concept
technologies	O
added	O
to	O
existing	O
client-server	O
relational	B-Application
databases	I-Application
like	O
PostgreSQL	B-Application
.	O
</s>
<s>
Some	O
experts	O
define	O
DistributedSQL	O
databases	B-Application
as	O
a	O
more	O
specific	O
subset	O
of	O
NewSQL	B-General_Concept
databases	B-Application
.	O
</s>
