<s>
CrateDB	B-Application
is	O
a	O
distributed	O
SQL	O
database	B-Application
management	I-Application
system	I-Application
that	O
integrates	O
a	O
fully	O
searchable	O
document-oriented	B-General_Concept
data	B-General_Concept
store	I-General_Concept
.	O
</s>
<s>
It	O
is	O
open-source	B-Application
,	O
written	O
in	O
Java	B-Language
,	O
based	O
on	O
a	O
shared-nothing	B-Operating_System
architecture	I-Operating_System
,	O
and	O
designed	O
for	O
high	O
scalability	O
.	O
</s>
<s>
CrateDB	B-Application
includes	O
components	O
from	O
Trino	B-Language
,	O
Lucene	B-Language
,	O
Elasticsearch	B-Application
and	O
Netty	B-Language
.	O
</s>
<s>
The	O
CrateDB	B-Application
project	O
was	O
started	O
by	O
Christian	O
Lutz	O
,	O
Bernd	O
Dorn	O
,	O
and	O
Jodok	O
Batlogg	O
,	O
an	O
open	O
source	O
contributor	O
and	O
creator	O
who	O
has	O
contributed	O
to	O
the	O
Open	O
Source	O
Initiative	O
Vorarlberg	O
while	O
at	O
Lovely	O
Systems	O
in	O
Dornbirn	O
.	O
</s>
<s>
In	O
December	O
,	O
CrateDB	B-Application
1.0	O
was	O
released	O
having	O
more	O
than	O
one	O
million	O
downloads	O
.	O
</s>
<s>
CrateDB	B-Application
2.0	O
,	O
the	O
first	O
Enterprise	O
Edition	O
of	O
CrateDB	B-Application
,	O
was	O
released	O
in	O
May	O
2017	O
after	O
a	O
$2.5	O
M	O
round	O
from	O
Dawn	O
Capital	O
,	O
Draper	O
Esprit	O
,	O
Speedinvest	O
,	O
and	O
Sunstone	O
Capital	O
.	O
</s>
<s>
CrateDB	B-Application
operates	O
in	O
a	O
shared-nothing	B-Operating_System
architecture	I-Operating_System
as	O
a	O
cluster	O
of	O
identically	O
configured	O
servers	O
(	O
nodes	O
)	O
.	O
</s>
<s>
CrateDB	B-Application
's	O
SQL	O
syntax	O
includes	O
JOINs	O
,	O
aggregations	O
,	O
indexes	O
,	O
sub-queries	O
,	O
user-defined	O
functions	O
,	O
and	O
views	O
.	O
</s>
<s>
For	O
query	O
distribution	O
,	O
CrateDB	B-Application
implements	O
memory-resident	O
columnar	O
field	O
caches	O
on	O
each	O
shard	O
.	O
</s>
<s>
CrateDB	B-Application
supports	O
“	O
strict	O
”	O
,	O
“	O
dynamic	O
”	O
,	O
or	O
“	O
ignored	O
”	O
schemas	O
:	O
</s>
<s>
Strict	O
schema	O
:	O
if	O
an	O
INSERT	O
statement	O
includes	O
a	O
column	O
that	O
was	O
n’t	O
defined	O
in	O
the	O
table	O
,	O
CrateDB	B-Application
enforces	O
the	O
original	O
schema	O
by	O
rejecting	O
the	O
INSERT	O
and	O
throwing	O
an	O
error	O
.	O
</s>
<s>
Dynamic	O
schema	O
:	O
CrateDB	B-Application
automatically	O
updates	O
the	O
schema	O
by	O
indexing	O
the	O
new	O
column	O
.	O
</s>
<s>
Ignored	O
schema	O
:	O
CrateDB	B-Application
does	O
n’t	O
index	O
the	O
column	O
,	O
but	O
it	O
stores	O
the	O
plain	O
JSON	O
value	O
.	O
</s>
<s>
CrateDB	B-Application
implements	O
an	O
eventually	B-General_Concept
consistent	I-General_Concept
,	O
non-blocking	O
data	O
insertion	O
model	O
.	O
</s>
<s>
It	O
includes	O
record	O
versioning	O
,	O
optimistic	B-Operating_System
concurrency	I-Operating_System
control	I-Operating_System
,	O
and	O
a	O
table-level	O
refresh	O
frequency	O
setting	O
,	O
which	O
forces	O
CrateDB	B-Application
data	O
to	O
become	O
consistent	O
every	O
n	O
milliseconds	O
.	O
</s>
<s>
CrateDB	B-Application
supports	O
read-after-write	O
consistency	O
:	O
the	O
queries	O
retrieving	O
a	O
specific	O
row	O
by	O
its	O
primary	O
key	O
always	O
receive	O
the	O
most	O
recent	O
row	O
.	O
</s>
<s>
An	O
IndexReader	O
is	O
always	O
bound	O
to	O
the	O
Lucene	B-Language
segment	O
from	O
which	O
it	O
was	O
started	O
,	O
meaning	O
it	O
has	O
to	O
be	O
refreshed	O
in	O
order	O
to	O
see	O
new	O
changes	O
.	O
</s>
<s>
In	O
CrateDB	B-Application
,	O
only	O
the	O
refresh	O
of	O
the	O
IndexReader	O
affects	O
consistency	O
.	O
</s>
<s>
CrateDB	B-Application
implements	O
WAL	O
(	O
write-ahead	B-Algorithm
logging	I-Algorithm
)	O
:	O
</s>
<s>
Operations	O
on	O
rows	O
(	O
which	O
are	O
internally	O
stored	O
in	O
CrateDB	B-Application
as	O
JSON	O
documents	O
)	O
are	O
atomic	O
.	O
</s>
<s>
Operations	O
on	O
rows	O
are	O
persisted	O
to	O
disk	O
without	O
having	O
to	O
issue	O
a	O
Lucene-commit	O
for	O
every	O
write	O
operation	O
.	O
</s>
<s>
When	O
the	O
translog	O
gets	O
flushed	O
,	O
all	O
data	O
is	O
written	O
to	O
the	O
persistent	O
index	O
storage	O
of	O
Lucene	B-Language
,	O
and	O
the	O
translog	O
gets	O
cleared	O
.	O
</s>
