<s>
Sherpa	O
is	O
Yahoo	B-Application
!	I-Application
</s>
<s>
'	O
s	O
next-generation	O
cloud	O
storage	O
platform	B-Device
.	O
</s>
<s>
It	O
is	O
a	O
hosted	O
,	O
distributed	O
,	O
and	O
geographically	O
replicated	O
key-value	B-Data_Structure
data	I-Data_Structure
store	I-Data_Structure
.	O
</s>
<s>
The	O
service	O
is	O
a	O
NoSQL	B-General_Concept
system	O
that	O
has	O
been	O
developed	O
by	O
Yahoo	O
!,	O
to	O
address	O
the	O
scalability	O
,	O
availability	O
,	O
and	O
latency	O
needs	O
of	O
the	O
conglomerate	O
’s	O
websites	O
.	O
</s>
<s>
Sherpa	O
has	O
abilities	O
such	O
as	O
elastic	O
growth	O
,	O
multi-tenancy	O
,	O
global	O
footprint	O
for	O
local	O
low-latency	O
access	O
,	O
asynchronous	O
replication	B-Architecture
,	O
representational	B-Protocol
state	I-Protocol
transfer	I-Protocol
(	O
REST	O
)	O
based	O
web	O
service	O
APIs	O
,	O
novel	O
per-record	O
consistency	O
knobs	O
,	O
high	O
availability	O
,	O
compression	O
,	O
secondary	O
indexes	O
,	O
and	O
record-level	O
replication	B-Architecture
.	O
</s>
<s>
A	O
table	O
is	O
shared	B-General_Concept
into	O
smaller	O
pieces	O
called	O
tablets	O
.	O
</s>
<s>
Data	O
is	O
shared	B-General_Concept
based	O
on	O
the	O
hash	B-Error_Name
value	I-Error_Name
of	O
the	O
key	O
,	O
or	O
range	O
partitioned	O
.	O
</s>
<s>
Sherpa	O
's	O
data	O
model	O
is	O
a	O
key-value	B-Data_Structure
store	I-Data_Structure
where	O
data	O
is	O
stored	O
as	O
JSON	B-General_Concept
blobs	B-General_Concept
.	O
</s>
<s>
Customers	O
can	O
choose	O
a	O
variety	O
of	O
table	O
types	O
:	O
distributed	B-Operating_System
hash	I-Operating_System
table	I-Operating_System
,	O
distributed	O
ordered	O
table	O
,	O
and	O
mastered	O
and	O
merging	O
tables	O
.	O
</s>
<s>
Data	O
is	O
automatically	O
replicated	O
to	O
multiple	O
nodes	O
for	O
fault	B-General_Concept
tolerance	I-General_Concept
.	O
</s>
<s>
Replication	B-Architecture
across	O
multiple	O
data	O
centers	O
is	O
supported	O
.	O
</s>
<s>
Sherpa	O
relies	O
on	O
a	O
reliable	O
transaction	O
message	O
bus	B-Application
for	O
replicating	O
transactions	O
.	O
</s>
<s>
This	O
message	O
bus	B-Application
guarantees	O
at-least-once	O
delivery	O
of	O
transaction	O
messages	O
.	O
</s>
<s>
Sherpa	O
supports	O
different	O
levels	O
of	O
consistency	O
,	O
ranging	O
from	O
per-record	O
timeline	O
consistency	O
where	O
all	O
writes	O
are	O
serialized	O
to	O
a	O
master	O
copy	O
,	O
to	O
eventual	B-General_Concept
consistency	I-General_Concept
.	O
</s>
<s>
Replication	B-Architecture
granularity	B-Operating_System
occurs	O
at	O
the	O
levels	O
of	O
records	O
and	O
tables	O
.	O
</s>
