<s>
Database	B-General_Concept
caching	I-General_Concept
is	O
a	O
process	O
included	O
in	O
the	O
design	O
of	O
computer	B-Application
applications	I-Application
which	O
generate	O
web	O
pages	O
on-demand	O
(	O
dynamically	O
)	O
by	O
accessing	O
backend	O
databases	B-Application
.	O
</s>
<s>
When	O
these	O
applications	O
are	O
deployed	O
on	O
multi-tier	B-Operating_System
environments	O
that	O
involve	O
browser-based	O
clients	O
,	O
web	O
application	O
servers	O
and	O
backend	O
databases	B-Application
,	O
middle-tier	O
database	B-General_Concept
caching	I-General_Concept
is	O
used	O
to	O
achieve	O
high	O
scalability	O
and	O
performance	O
.	O
</s>
<s>
In	O
a	O
three	B-Operating_System
tier	I-Operating_System
architecture	I-Operating_System
,	O
the	O
application	B-Application
software	I-Application
tier	B-Operating_System
and	O
data	B-General_Concept
storage	I-General_Concept
tier	B-Operating_System
can	O
be	O
in	O
different	O
hosts	O
.	O
</s>
<s>
Throughput	O
of	O
an	O
application	O
can	O
be	O
limited	O
by	O
the	O
network	B-Architecture
speed	O
.	O
</s>
<s>
This	O
limitation	O
can	O
be	O
minimized	O
by	O
having	O
the	O
database	O
at	O
the	O
application	O
tier	B-Operating_System
.	O
</s>
<s>
In	O
this	O
case	O
,	O
a	O
more	O
light-weight	O
database	O
application	O
can	O
be	O
used	O
to	O
cache	O
data	O
from	O
the	O
commercial	O
database	B-Application
management	I-Application
system	I-Application
.	O
</s>
<s>
Database	B-General_Concept
caching	I-General_Concept
improves	O
scalability	O
by	O
distributing	O
query	O
workload	O
from	O
backend	O
to	O
multiple	O
cheap	O
front-end	O
systems	O
.	O
</s>
<s>
Another	O
benefit	O
is	O
improved	O
data	O
access	O
speeds	O
brought	O
about	O
by	O
locality	O
of	O
data	O
and	O
smoothing	O
out	O
load	O
peaks	O
by	O
avoiding	O
round-trips	O
between	O
middle-tier	O
and	O
data-tier	O
.	O
</s>
<s>
Multiple	O
cache	O
granularity	O
-	O
Database	O
level	O
,	O
Table	O
level	O
and	O
Result-set	O
caching	O
:	O
Major	O
portions	O
of	O
corporate	O
databases	B-Application
are	O
historical	O
and	O
infrequently	O
accessed	O
.	O
</s>
<s>
Horizontally	O
scalable	O
:	O
Cluster	B-Architecture
computing	I-Architecture
may	O
increase	O
availability	O
and	O
achieve	O
load	O
balancing	O
.	O
</s>
<s>
Transparent	O
access	O
to	O
non-cached	O
tables	O
reside	O
in	O
target	O
database	O
:	O
Database	B-General_Concept
cache	I-General_Concept
should	O
keep	O
track	O
of	O
queries	O
and	O
should	O
be	O
able	O
to	O
intelligently	O
route	O
to	O
the	O
database	B-General_Concept
cache	I-General_Concept
or	O
to	O
the	O
origin	O
database	O
based	O
on	O
the	O
data	O
locality	O
without	O
any	O
application	O
code	O
modification	O
.	O
</s>
<s>
Cache	O
walking	O
on	O
deletes	O
or	O
invalidation	O
events	O
:	O
Cache	O
designs	O
that	O
leverage	O
external	O
cache	O
engines	O
such	O
as	O
Redis	B-Operating_System
or	O
Hazelcast	B-Application
will	O
often	O
trigger	O
invalidation	O
by	O
issuing	O
deletions	O
against	O
the	O
invalidated	O
objects	O
.	O
</s>
<s>
Engines	O
such	O
as	O
Redis	B-Operating_System
and	O
Hazelcast	B-Application
provide	O
for	O
key	O
change	O
notification	O
support	O
however	O
,	O
allowing	O
local	O
cache	O
layers	O
to	O
be	O
updated	O
when	O
keys	O
are	O
changed	O
in	O
a	O
remote	O
cache	O
layer	O
.	O
</s>
