<s>
Apache	B-Application
Flink	I-Application
is	O
an	O
open-source	B-Application
,	O
unified	O
stream-processing	B-Application
and	O
batch-processing	B-General_Concept
framework	B-Architecture
developed	O
by	O
the	O
Apache	O
Software	O
Foundation	O
.	O
</s>
<s>
The	O
core	O
of	O
Apache	B-Application
Flink	I-Application
is	O
a	O
distributed	O
streaming	O
data-flow	B-Application
engine	O
written	O
in	O
Java	B-Language
and	O
Scala	B-Application
.	O
</s>
<s>
Flink	O
executes	O
arbitrary	O
dataflow	B-Application
programs	O
in	O
a	O
data-parallel	B-Operating_System
and	O
pipelined	B-Operating_System
(	O
hence	O
task	B-Operating_System
parallel	I-Operating_System
)	O
manner	O
.	O
</s>
<s>
Flink	O
's	O
pipelined	B-Operating_System
runtime	O
system	O
enables	O
the	O
execution	O
of	O
bulk/batch	B-General_Concept
and	O
stream	B-Application
processing	I-Application
programs	O
.	O
</s>
<s>
Furthermore	O
,	O
Flink	O
's	O
runtime	O
supports	O
the	O
execution	O
of	O
iterative	B-Algorithm
algorithms	I-Algorithm
natively	O
.	O
</s>
<s>
Programs	O
can	O
be	O
written	O
in	O
Java	B-Language
,	O
Scala	B-Application
,	O
Python	B-Language
,	O
and	O
SQL	B-Language
and	O
are	O
automatically	O
compiled	O
and	O
optimized	O
into	O
dataflow	B-Application
programs	O
that	O
are	O
executed	O
in	O
a	O
cluster	O
or	O
cloud	O
environment	O
.	O
</s>
<s>
Flink	O
does	O
not	O
provide	O
its	O
own	O
data-storage	O
system	O
,	O
but	O
provides	O
data-source	O
and	O
sink	O
connectors	O
to	O
systems	O
such	O
as	O
Apache	O
Doris	O
,	O
Amazon	O
Kinesis	O
,	O
Apache	B-Language
Kafka	I-Language
,	O
HDFS	O
,	O
Apache	B-Application
Cassandra	I-Application
,	O
and	O
ElasticSearch	B-Application
.	O
</s>
<s>
Apache	B-Application
Flink	I-Application
is	O
developed	O
under	O
the	O
Apache	B-Application
License	I-Application
2.0	I-Application
by	O
the	O
Apache	B-Application
Flink	I-Application
Community	O
within	O
the	O
Apache	O
Software	O
Foundation	O
.	O
</s>
<s>
Apache	B-Application
Flink	I-Application
's	O
dataflow	B-Application
programming	I-Application
model	I-Application
provides	O
event-at-a-time	O
processing	O
on	O
both	O
finite	O
and	O
infinite	O
datasets	O
.	O
</s>
<s>
Apache	B-Application
Flink	I-Application
includes	O
two	O
core	O
APIs	O
:	O
a	O
DataStream	O
API	O
for	O
bounded	O
or	O
unbounded	O
streams	O
of	O
data	O
and	O
a	O
DataSet	O
API	O
for	O
bounded	O
data	O
sets	O
.	O
</s>
<s>
Flink	O
also	O
offers	O
a	O
Table	O
API	O
,	O
which	O
is	O
a	O
SQL-like	O
expression	O
language	O
for	O
relational	O
stream	O
and	O
batch	B-General_Concept
processing	I-General_Concept
that	O
can	O
be	O
easily	O
embedded	O
in	O
Flink	O
's	O
DataStream	O
and	O
DataSet	O
APIs	O
.	O
</s>
<s>
The	O
highest-level	O
language	O
supported	O
by	O
Flink	O
is	O
SQL	B-Language
,	O
which	O
is	O
semantically	O
similar	O
to	O
the	O
Table	O
API	O
and	O
represents	O
programs	O
as	O
SQL	B-Language
query	O
expressions	O
.	O
</s>
<s>
Upon	O
execution	O
,	O
Flink	O
programs	O
are	O
mapped	O
to	O
streaming	O
dataflows	B-Application
.	O
</s>
<s>
Every	O
Flink	O
dataflow	B-Application
starts	O
with	O
one	O
or	O
more	O
sources	O
(	O
a	O
data	O
input	O
,	O
e.g.	O
,	O
a	O
message	O
queue	O
or	O
a	O
file	O
system	O
)	O
and	O
ends	O
with	O
one	O
or	O
more	O
sinks	O
(	O
a	O
data	O
output	O
,	O
e.g.	O
,	O
a	O
message	O
queue	O
,	O
file	O
system	O
,	O
or	O
database	O
)	O
.	O
</s>
<s>
These	O
streams	O
can	O
be	O
arranged	O
as	O
a	O
directed	O
,	O
acyclic	O
dataflow	B-Application
graph	O
,	O
allowing	O
an	O
application	O
to	O
branch	O
and	O
merge	O
dataflows	B-Application
.	O
</s>
<s>
Flink	O
offers	O
ready-built	O
source	O
and	O
sink	O
connectors	O
with	O
Apache	B-Language
Kafka	I-Language
,	O
Amazon	O
Kinesis	O
,	O
HDFS	O
,	O
Apache	B-Application
Cassandra	I-Application
,	O
and	O
more	O
.	O
</s>
<s>
Apache	B-Application
Flink	I-Application
includes	O
a	O
lightweight	O
fault	O
tolerance	O
mechanism	O
based	O
on	O
distributed	O
checkpoints	O
.	O
</s>
<s>
The	O
DataStream	O
API	O
includes	O
more	O
than	O
20	O
different	O
types	O
of	O
transformations	O
and	O
is	O
available	O
in	O
Java	B-Language
and	O
Scala	B-Application
.	O
</s>
<s>
A	O
simple	O
example	O
of	O
a	O
stateful	O
stream	B-Application
processing	I-Application
program	O
is	O
an	O
application	O
that	O
emits	O
a	O
word	O
count	O
from	O
a	O
continuous	O
input	O
stream	O
and	O
groups	O
the	O
data	O
in	O
5-second	O
windows	O
:	O
</s>
<s>
Apache	B-Language
Beam	I-Language
“	O
provides	O
an	O
advanced	O
unified	O
programming	O
model	O
,	O
allowing	O
(	O
a	O
developer	O
)	O
to	O
implement	O
batch	O
and	O
streaming	O
data	O
processing	O
jobs	O
that	O
can	O
run	O
on	O
any	O
execution	O
engine.	O
”	O
The	O
Apache	O
Flink-on-Beam	O
runner	O
is	O
the	O
most	O
feature-rich	O
according	O
to	O
a	O
capability	O
matrix	O
maintained	O
by	O
the	O
Beam	O
community	O
.	O
</s>
<s>
data	O
Artisans	O
,	O
in	O
conjunction	O
with	O
the	O
Apache	B-Application
Flink	I-Application
community	O
,	O
worked	O
closely	O
with	O
the	O
Beam	O
community	O
to	O
develop	O
a	O
Flink	O
runner	O
.	O
</s>
<s>
The	O
API	O
is	O
available	O
in	O
Java	B-Language
,	O
Scala	B-Application
and	O
an	O
experimental	O
Python	B-Language
API	O
.	O
</s>
<s>
Flink	O
's	O
Table	O
API	O
is	O
a	O
SQL-like	O
expression	O
language	O
for	O
relational	O
stream	O
and	O
batch	B-General_Concept
processing	I-General_Concept
that	O
can	O
be	O
embedded	O
in	O
Flink	O
's	O
Java	B-Language
and	O
Scala	B-Application
DataSet	O
and	O
DataStream	O
APIs	O
.	O
</s>
<s>
The	O
Table	O
API	O
and	O
SQL	B-Language
interface	O
operate	O
on	O
a	O
relational	O
Table	O
abstraction	O
.	O
</s>
<s>
Tables	O
can	O
also	O
be	O
queried	O
with	O
regular	O
SQL	B-Language
.	O
</s>
<s>
The	O
Table	O
API	O
and	O
SQL	B-Language
offer	O
equivalent	O
functionality	O
and	O
can	O
be	O
mixed	O
in	O
the	O
same	O
program	O
.	O
</s>
<s>
When	O
a	O
Table	O
is	O
converted	O
back	O
into	O
a	O
DataSet	O
or	O
DataStream	O
,	O
the	O
logical	O
plan	O
,	O
which	O
was	O
defined	O
by	O
relational	O
operators	O
and	O
SQL	B-Language
queries	O
,	O
is	O
optimized	O
using	O
Apache	B-Language
Calcite	I-Language
and	O
is	O
transformed	O
into	O
a	O
DataSet	O
or	O
DataStream	O
program	O
.	O
</s>
<s>
Flink	O
Forward	O
is	O
an	O
annual	O
conference	O
about	O
Apache	B-Application
Flink	I-Application
.	O
</s>
<s>
It	O
features	O
keynotes	O
,	O
talks	O
from	O
Flink	O
users	O
in	O
industry	O
and	O
academia	O
,	O
and	O
hands-on	O
training	O
sessions	O
on	O
Apache	B-Application
Flink	I-Application
.	O
</s>
<s>
Instead	O
,	O
the	O
conference	O
was	O
hosted	O
virtually	O
,	O
starting	O
on	O
April	O
22nd	O
and	O
concluding	O
on	O
April	O
24th	O
,	O
featuring	O
live	O
keynotes	O
,	O
Flink	O
use	O
cases	O
,	O
Apache	B-Application
Flink	I-Application
internals	O
,	O
and	O
other	O
topics	O
on	O
stream	B-Application
processing	I-Application
and	O
real-time	O
analytics	O
.	O
</s>
<s>
Flink	O
started	O
from	O
a	O
fork	O
of	O
Stratosphere	O
's	O
distributed	O
execution	O
engine	O
and	O
it	O
became	O
an	O
Apache	B-Application
Incubator	I-Application
project	O
in	O
March	O
2014	O
.	O
</s>
<s>
The	O
1.14.1	O
,	O
1.13.4	O
,	O
1.12.6	O
,	O
1.11.5	O
releases	O
,	O
which	O
were	O
supposed	O
to	O
only	O
contain	O
a	O
Log4j	B-Application
upgrade	O
to	O
2.15.0	O
,	O
were	O
skipped	O
because	O
was	O
discovered	O
during	O
the	O
release	O
publication	O
.	O
</s>
