<s>
Amazon	B-General_Concept
ElastiCache	I-General_Concept
is	O
a	O
fully	O
managed	O
in-memory	B-General_Concept
data	O
store	O
and	O
cache	B-General_Concept
service	O
by	O
Amazon	B-Application
Web	I-Application
Services	I-Application
(	O
AWS	B-Application
)	O
.	O
</s>
<s>
The	O
service	O
improves	O
the	O
performance	O
of	O
web	O
applications	O
by	O
retrieving	O
information	O
from	O
managed	O
in-memory	B-General_Concept
caches	B-General_Concept
,	O
instead	O
of	O
relying	O
entirely	O
on	O
slower	O
disk-based	O
databases	O
.	O
</s>
<s>
ElastiCache	O
supports	O
two	O
open-source	O
in-memory	B-General_Concept
caching	B-General_Concept
engines	O
:	O
Memcached	B-Application
and	O
Redis	B-Operating_System
(	O
also	O
called	O
"	O
ElastiCache	O
for	O
Redis	B-Operating_System
"	O
)	O
.	O
</s>
<s>
As	O
a	O
web	O
service	O
running	O
in	O
the	O
computing	B-Architecture
cloud	I-Architecture
,	O
Amazon	B-General_Concept
ElastiCache	I-General_Concept
is	O
designed	O
to	O
simplify	O
the	O
setup	O
,	O
operation	O
,	O
and	O
scaling	O
of	O
memcached	B-Application
and	O
Redis	B-Operating_System
deployments	O
.	O
</s>
<s>
Scaling	O
ElastiCache	O
resources	O
can	O
be	O
performed	O
by	O
a	O
single	O
API	B-General_Concept
call	O
.	O
</s>
<s>
Amazon	B-General_Concept
ElastiCache	I-General_Concept
was	O
first	O
released	O
on	O
August	O
22	O
,	O
2011	O
,	O
supporting	O
memcached	B-Application
.	O
</s>
<s>
This	O
was	O
followed	O
by	O
support	O
for	O
reserved	O
instances	O
on	O
April	O
5	O
,	O
2012	O
and	O
Redis	B-Operating_System
on	O
September	O
4	O
,	O
2013	O
.	O
</s>
<s>
Database	O
limitations	O
are	O
often	O
a	O
bottleneck	O
for	O
application	B-Application
performance	O
.	O
</s>
<s>
By	O
placing	O
Amazon	B-General_Concept
ElastiCache	I-General_Concept
between	O
an	O
application	B-Application
and	O
its	O
database	O
tier	B-Operating_System
,	O
database	O
operations	O
can	O
be	O
accelerated	O
.	O
</s>
<s>
In	O
many	O
cases	O
,	O
the	O
cost	O
savings	O
outweigh	O
the	O
cache	B-General_Concept
costs	O
.	O
</s>
<s>
Using	O
the	O
Redis	B-Operating_System
engine	O
,	O
ElastiCache	O
can	O
rapidly	O
process	O
time-series	O
data	O
,	O
quickly	O
selecting	O
newest	O
or	O
oldest	O
records	O
or	O
events	O
within	O
range	O
of	O
a	O
point-in-time	O
.	O
</s>
<s>
Using	O
Amazon	B-General_Concept
ElastiCache	I-General_Concept
with	O
the	O
Redis	B-Operating_System
engine	O
can	O
enable	O
high-speed	O
at	O
scale	O
for	O
leaderboards	O
.	O
</s>
<s>
Some	O
APIs	B-General_Concept
only	O
allow	O
a	O
limited	O
number	O
of	O
requests	O
per	O
time	O
period	O
.	O
</s>
<s>
Amazon	B-General_Concept
ElastiCache	I-General_Concept
for	O
Redis	B-Operating_System
engine	O
can	O
use	O
incremental	O
counters	O
and	O
other	O
tools	O
to	O
throttle	O
API	B-General_Concept
access	O
to	O
meet	O
restrictions	O
.	O
</s>
<s>
Using	O
counters	O
can	O
create	O
a	O
race	B-Operating_System
condition	I-Operating_System
where	O
an	O
operation	O
is	O
allowed	O
because	O
a	O
counter	O
was	O
not	O
updated	O
promptly	O
.	O
</s>
<s>
Using	O
the	O
ElastiCache	O
for	O
Redis	B-Operating_System
atomic	O
counter	O
functions	O
,	O
where	O
a	O
single	O
operation	O
both	O
checks	O
and	O
increments	O
the	O
counter	O
's	O
value	O
,	O
prevents	O
race	B-Operating_System
conditions	I-Operating_System
.	O
</s>
<s>
ElastiCache	O
for	O
Redis	B-Operating_System
supports	O
publish-subscribe	B-Operating_System
patterns	I-Operating_System
,	O
which	O
enable	O
the	O
creation	O
of	O
chat	O
rooms	O
and	O
message	O
boards	O
where	O
messages	O
are	O
automatically	O
distributed	O
to	O
interested	O
users	O
.	O
</s>
<s>
Amazon	B-General_Concept
ElastiCache	I-General_Concept
can	O
use	O
on-demand	O
cache	B-General_Concept
nodes	O
or	O
reserved	O
cache	B-General_Concept
nodes	O
.	O
</s>
<s>
On-demand	O
nodes	O
provide	O
cache	B-General_Concept
capacity	O
by	O
the	O
hour	O
,	O
with	O
resources	O
in	O
the	O
AWS	B-Application
cloud	O
assigned	O
when	O
a	O
cache	B-General_Concept
node	O
is	O
provisioned	O
.	O
</s>
<s>
Reserved	O
nodes	O
require	O
a	O
1-year	O
or	O
3-year	O
commitment	O
,	O
which	O
dedicates	O
cache	B-General_Concept
resources	O
to	O
the	O
owner	O
.	O
</s>
<s>
An	O
efficient	O
cache	B-General_Concept
can	O
significantly	O
increase	O
application	B-Application
's	O
performance	O
and	O
user	O
navigation	O
speed	O
.	O
</s>
<s>
Amazon	B-Application
CloudWatch	O
exposes	O
ElastiCache	O
performance	O
metrics	O
that	O
can	O
be	O
tracked	O
.	O
</s>
<s>
Many	O
ElastiCache	O
metrics	O
can	O
be	O
collected	O
from	O
AWS	B-Application
via	O
CloudWatch	O
or	O
directly	O
from	O
the	O
cache	B-General_Concept
engine	O
,	O
whether	O
Redis	B-Operating_System
or	O
Memcached	B-Application
,	O
with	O
a	O
monitoring	O
tool	O
integrating	O
with	O
it	O
:	O
</s>
<s>
Metrics	O
related	O
to	O
ElastiCache	O
can	O
also	O
be	O
retrieved	O
using	O
command	B-Application
lines	I-Application
.	O
</s>
<s>
The	O
third	O
way	O
to	O
collect	O
ElastiCache	O
metrics	O
is	O
via	O
a	O
dedicated	O
monitoring	O
tool	O
integrating	O
with	O
Amazon	B-Application
CloudWatch	O
.	O
</s>
<s>
As	O
an	O
AWS	B-Application
service	O
,	O
ElastiCache	O
is	O
designed	O
to	O
be	O
accessed	O
exclusively	O
from	O
within	O
AWS	B-Application
,	O
though	O
it	O
is	O
possible	O
to	O
connect	O
the	O
service	O
to	O
applications	O
and	O
databases	O
that	O
are	O
not	O
hosted	O
by	O
AWS	B-Application
.	O
</s>
<s>
Other	O
vendors	O
provide	O
cloud	O
data	O
cache	B-General_Concept
services	O
comparable	O
to	O
Amazon	B-General_Concept
ElastiCache	I-General_Concept
,	O
including	O
,	O
Redis	B-Operating_System
Ltd	O
(	O
company	O
behind	O
open	O
source	O
Redis	B-Operating_System
and	O
Redis	B-Operating_System
Enterprise	O
)	O
,	O
Redis	B-Operating_System
To	O
Go	O
,	O
IBM	B-General_Concept
Compose	I-General_Concept
,	O
Oracle	O
Application	B-Application
Container	O
Cloud	B-Architecture
Service	I-Architecture
,	O
and	O
Rackspace	O
ObjectRocket	O
.	O
</s>
