<s>
Gizzard	B-Language
is	O
an	O
open	B-Application
source	I-Application
sharding	B-General_Concept
framework	B-Architecture
to	O
create	O
custom	O
fault-tolerant	B-General_Concept
,	O
distributed	B-Operating_System
databases	I-Operating_System
.	O
</s>
<s>
It	O
was	O
initially	O
used	O
by	O
Twitter	B-Application
and	O
emerged	O
from	O
a	O
wide	O
variety	O
of	O
data	O
storage	O
problems	O
.	O
</s>
<s>
Gizzard	B-Language
operates	O
as	O
a	O
middleware	B-General_Concept
networking	O
service	O
that	O
runs	O
on	O
the	O
Java	B-Language
Virtual	I-Language
Machine	I-Language
.	O
</s>
<s>
It	O
manages	O
partitioning	B-General_Concept
data	O
across	O
arbitrary	O
backend	O
datastores	O
,	O
that	O
allows	O
it	O
to	O
be	O
accessed	O
efficiently	O
.	O
</s>
<s>
The	O
partitioning	B-General_Concept
rules	O
are	O
stored	O
in	O
a	O
forwarding	O
table	O
that	O
maps	O
key	O
ranges	O
to	O
partitions	B-General_Concept
.	O
</s>
<s>
Each	O
partition	B-General_Concept
manages	O
its	O
own	O
replication	B-Architecture
through	O
a	O
declarative	O
replication	B-Architecture
tree	O
.	O
</s>
<s>
Gizzard	B-Language
handles	O
both	O
physical	O
and	O
logical	O
shards	B-General_Concept
.	O
</s>
<s>
Physical	O
shards	B-General_Concept
point	O
to	O
a	O
physical	O
database	B-Application
backend	I-Application
whereas	O
logical	O
shards	B-General_Concept
are	O
trees	O
of	O
other	O
shards	B-General_Concept
.	O
</s>
<s>
In	O
addition	O
Gizzard	B-Language
also	O
supports	O
migrations	B-General_Concept
and	O
gracefully	O
handles	O
failures	O
.	O
</s>
<s>
Gizzard	B-Language
is	O
available	O
at	O
GitHub	B-Application
and	O
licensed	O
under	O
the	O
Apache	B-Application
License	I-Application
2.0	O
.	O
</s>
