<s>
In	O
database	O
computing	O
,	O
Oracle	B-Application
Real	B-Operating_System
Application	I-Operating_System
Clusters	I-Operating_System
(	O
RAC	O
)	O
—	O
an	O
option	O
for	O
the	O
Oracle	B-General_Concept
Database	I-General_Concept
software	O
produced	O
by	O
Oracle	B-Application
Corporation	I-Application
and	O
introduced	O
in	O
2001	O
with	O
Oracle9i	B-General_Concept
—	O
provides	O
software	O
for	O
clustering	B-Architecture
and	O
high	O
availability	O
in	O
Oracle	B-General_Concept
database	I-General_Concept
environments	O
.	O
</s>
<s>
Oracle	B-Application
Corporation	I-Application
includes	O
RAC	O
with	O
the	O
Enterprise	O
Edition	O
,	O
provided	O
the	O
nodes	O
are	O
clustered	O
using	O
Oracle	B-Operating_System
Clusterware	I-Operating_System
.	O
</s>
<s>
Oracle	B-Operating_System
RAC	I-Operating_System
allows	O
multiple	O
computers	O
to	O
run	O
Oracle	B-General_Concept
RDBMS	I-General_Concept
software	O
simultaneously	O
while	O
accessing	O
a	O
single	O
database	O
,	O
thus	O
providing	O
clustering	B-Architecture
.	O
</s>
<s>
In	O
a	O
non-RAC	O
Oracle	B-General_Concept
database	I-General_Concept
,	O
a	O
single	O
instance	O
accesses	O
a	O
single	O
database	O
.	O
</s>
<s>
The	O
database	O
consists	O
of	O
a	O
collection	O
of	O
data	B-General_Concept
files	I-General_Concept
,	O
control	O
files	O
,	O
and	O
redo	B-Application
logs	I-Application
located	O
on	O
disk	B-Device
.	O
</s>
<s>
The	O
instance	O
comprises	O
the	O
collection	O
of	O
Oracle-related	O
memory	O
and	O
background	O
processes	O
that	O
run	O
on	O
a	O
computer	O
system	O
.	O
</s>
<s>
In	O
an	O
Oracle	B-Operating_System
RAC	I-Operating_System
environment	O
,	O
2	O
or	O
more	O
instances	O
concurrently	O
access	O
a	O
single	O
database	O
.	O
</s>
<s>
The	O
main	O
aim	O
of	O
Oracle	B-Operating_System
RAC	I-Operating_System
is	O
to	O
implement	O
a	O
clustered	O
database	O
to	O
provide	O
performance	O
,	O
scalability	B-Architecture
and	O
resilience	O
&	O
high	O
availability	O
of	O
data	O
at	O
instance	O
level	O
.	O
</s>
<s>
Oracle	B-Operating_System
RAC	I-Operating_System
depends	O
on	O
the	O
infrastructure	O
component	O
Oracle	B-Operating_System
Clusterware	I-Operating_System
to	O
coordinate	O
multiple	O
servers	O
and	O
their	O
sharing	O
of	O
data	O
storage	O
.	O
</s>
<s>
Prior	O
to	O
Oracle	B-Application
9	O
,	O
network-clustered	O
Oracle	B-General_Concept
databases	I-General_Concept
used	O
a	O
storage	O
device	O
as	O
the	O
data-transfer	O
medium	O
(	O
meaning	O
that	O
one	O
node	O
would	O
write	O
a	O
data	O
block	O
to	O
disk	B-Device
and	O
another	O
node	O
would	O
read	O
that	O
data	O
from	O
the	O
same	O
disk	B-Device
)	O
,	O
which	O
had	O
the	O
inherent	O
disadvantage	O
of	O
lackluster	O
performance	O
.	O
</s>
<s>
Oracle	B-Application
9i	O
addressed	O
this	O
issue	O
:	O
RAC	O
uses	O
a	O
dedicated	O
network	O
connection	O
for	O
communications	O
internal	O
to	O
the	O
cluster	O
.	O
</s>
<s>
Oracle	B-Operating_System
RAC	I-Operating_System
refers	O
to	O
this	O
functionality	O
as	O
Cache	B-General_Concept
Fusion	O
.	O
</s>
<s>
Cache	B-General_Concept
Fusion	O
involves	O
the	O
ability	O
of	O
Oracle	B-Operating_System
RAC	I-Operating_System
to	O
"	O
fuse	O
"	O
the	O
in-memory	O
data	O
cached	O
physically	O
separately	O
on	O
each	O
computer	O
into	O
a	O
single	O
,	O
global	O
cache	B-General_Concept
.	O
</s>
<s>
The	O
Oracle	B-Application
Grid	O
Naming	O
Service	O
(	O
GNS	O
)	O
handles	O
name	B-Library
resolution	I-Library
in	O
the	O
cluster	O
registry	O
.	O
</s>
<s>
Oracle	B-Application
Real	B-Operating_System
Application	I-Operating_System
Clusters	I-Operating_System
12c	O
Release	O
1	O
Enterprise	O
Edition	O
.	O
</s>
<s>
Oracle	B-Application
Real	B-Operating_System
Application	I-Operating_System
Clusters	I-Operating_System
One	O
Node	O
(	O
RAC	O
One	O
Node	O
)	O
applies	O
RAC	O
to	O
single-node	O
installations	O
running	O
Oracle	B-General_Concept
Database	I-General_Concept
11g	O
Release	O
2	O
Enterprise	O
Edition	O
.	O
</s>
<s>
Relative	O
to	O
the	O
single-instance	O
Oracle	B-General_Concept
database	I-General_Concept
,	O
Oracle	B-Operating_System
RAC	I-Operating_System
adds	O
additional	O
complexity	O
.	O
</s>
<s>
Oracle	B-Application
Real	B-Operating_System
Application	I-Operating_System
Clusters	I-Operating_System
(	O
RAC	O
)	O
,	O
introduced	O
with	O
Oracle	B-Application
9i	O
in	O
2001	O
,	O
supersedes	O
the	O
Oracle	B-Application
Parallel	O
Server	O
(	O
OPS	O
)	O
database	O
option	O
.	O
</s>
<s>
Whereas	O
Oracle9i	B-General_Concept
required	O
an	O
external	O
clusterware	O
(	O
known	O
as	O
vendor	O
clusterware	O
like	O
TruCluster	B-General_Concept
Veritas	B-Operating_System
Cluster	I-Operating_System
Server	I-Operating_System
or	O
Sun	B-Operating_System
Cluster	I-Operating_System
)	O
for	O
most	O
of	O
the	O
Unix	O
flavors	O
(	O
except	O
for	O
Linux	O
and	O
Windows	O
where	O
Oracle	B-Application
provided	O
free	O
clusterware	O
called	O
Cluster	O
Ready	O
Services	O
or	O
CRS	O
)	O
,	O
as	O
of	O
Oracle	B-Application
10g	O
,	O
Oracle	B-Application
's	O
clusterware	O
product	O
was	O
available	O
for	O
all	O
operating	O
systems	O
.	O
</s>
<s>
With	O
the	O
release	O
of	O
Oracle	B-General_Concept
Database	I-General_Concept
10g	O
Release	O
2	O
(	O
10.2	O
)	O
,	O
Cluster	O
Ready	O
Services	O
was	O
renamed	O
to	O
Oracle	B-Operating_System
Clusterware	I-Operating_System
.	O
</s>
<s>
When	O
using	O
Oracle	B-Application
10g	O
or	O
higher	O
,	O
Oracle	B-Operating_System
Clusterware	I-Operating_System
is	O
the	O
only	O
clusterware	O
that	O
you	O
need	O
for	O
most	O
platforms	O
on	O
which	O
Oracle	B-Operating_System
RAC	I-Operating_System
operates	O
(	O
except	O
for	O
Tru	O
cluster	O
,	O
in	O
which	O
case	O
you	O
need	O
vendor	O
clusterware	O
)	O
.	O
</s>
<s>
You	O
can	O
still	O
use	O
clusterware	O
from	O
other	O
vendors	O
,	O
if	O
the	O
clusterware	O
is	O
certified	O
for	O
Oracle	B-Operating_System
RAC	I-Operating_System
.	O
</s>
<s>
In	O
RAC	O
,	O
the	O
write-transaction	O
must	O
take	O
ownership	O
of	O
the	O
relevant	O
area	O
of	O
the	O
database	O
:	O
typically	O
,	O
this	O
involves	O
a	O
request	O
across	O
the	O
cluster	O
interconnection	O
(	O
local	O
IP	O
network	O
)	O
to	O
transfer	O
the	O
data-block	B-General_Concept
ownership	O
from	O
another	O
node	O
to	O
the	O
one	O
wishing	O
to	O
do	O
the	O
write	O
.	O
</s>
<s>
For	O
many	O
types	O
of	O
applications	O
,	O
the	O
time	O
spent	O
coordinating	O
block	O
access	O
across	O
systems	O
is	O
low	O
relative	O
to	O
the	O
many	O
operations	O
on	O
the	O
system	O
,	O
and	O
RAC	O
will	O
scale	B-Architecture
comparably	O
to	O
a	O
single	O
system	O
.	O
</s>
<s>
(	O
Oracle	B-General_Concept
11g	I-General_Concept
has	O
made	O
many	O
enhancements	O
in	O
this	O
area	O
and	O
performs	O
a	O
lot	O
better	O
than	O
earlier	O
versions	O
for	O
read-only	O
workloads	O
.	O
)	O
</s>
<s>
This	O
makes	O
Oracle	B-Operating_System
RAC	I-Operating_System
horizontally	O
scalable	B-Architecture
with	O
many	O
nodes	O
.	O
</s>
<s>
Application	O
vendors	O
(	O
such	O
as	O
SAP	B-Application
)	O
use	O
Oracle	B-Operating_System
RAC	I-Operating_System
to	O
demonstrate	O
the	O
scalability	B-Architecture
of	O
their	O
application	O
.	O
</s>
<s>
Most	O
of	O
the	O
biggest	O
OLTP	B-General_Concept
benchmarks	O
are	O
on	O
Oracle	B-Operating_System
RAC	I-Operating_System
.	O
</s>
<s>
Oracle	B-Operating_System
RAC	I-Operating_System
11g	O
supports	O
up	O
to	O
100	O
nodes	O
.	O
</s>
<s>
An	O
application	O
that	O
scales	O
linearly	O
on	O
an	O
SMP	B-Operating_System
machine	O
may	O
scale	B-Architecture
linearly	O
under	O
RAC	O
.	O
</s>
<s>
However	O
,	O
if	O
the	O
application	O
cannot	O
scale	B-Architecture
linearly	O
on	O
SMP	B-Operating_System
,	O
it	O
will	O
not	O
scale	B-Architecture
when	O
ported	O
to	O
RAC	O
.	O
</s>
<s>
In	O
short	O
,	O
the	O
application	O
scalability	B-Architecture
is	O
based	O
on	O
how	O
well	O
the	O
application	O
scales	O
in	O
a	O
single	O
instance	O
.	O
</s>
<s>
Shared-nothing	B-Operating_System
and	O
shared-everything	O
architectures	O
each	O
have	O
advantages	O
over	O
the	O
other	O
.	O
</s>
<s>
DBMS	O
vendors	O
and	O
industry	O
analysts	O
regularly	O
debate	O
the	O
matter	O
;	O
for	O
example	O
,	O
Microsoft	O
touts	O
a	O
comparison	O
of	O
its	O
SQL	B-Application
Server	I-Application
2005	I-Application
with	O
Oracle	B-Application
10g	O
RAC	O
.	O
</s>
<s>
Oracle	B-Application
Corporation	I-Application
offered	O
a	O
Shared	B-Operating_System
Nothing	I-Operating_System
architecture	I-Operating_System
RDBMS	B-Application
with	O
the	O
advent	O
of	O
the	O
IBM	O
SP	O
and	O
SP2	O
with	O
the	O
release	O
of	O
7.x	O
MPP	O
editions	O
,	O
in	O
which	O
virtual	O
shared	O
drives	O
(	O
VSD	O
)	O
were	O
used	O
to	O
create	O
a	O
Shared	O
Everything	O
implementation	O
on	O
a	O
Shared	B-Operating_System
Nothing	I-Operating_System
architecture	I-Operating_System
.	O
</s>
<s>
Shared-everything	O
architectures	O
share	O
both	O
data	O
on	O
disk	B-Device
and	O
data	O
in	O
memory	O
between	O
nodes	O
in	O
the	O
cluster	O
.	O
</s>
<s>
This	O
is	O
in	O
contrast	O
to	O
"	O
shared-nothing	B-Operating_System
"	O
architectures	O
that	O
share	O
none	O
of	O
them	O
.	O
</s>
<s>
IBM	B-Application
Db2	I-Application
for	O
z/OS	B-Application
(	O
the	O
IBM	O
mainframe	O
operating-system	O
)	O
has	O
provided	O
a	O
high-performance	O
data-sharing	O
option	O
since	O
the	O
mid-1990s	O
when	O
IBM	O
released	O
its	O
mainframe	O
hardware	O
and	O
software-clustering	O
infrastructure	O
.	O
</s>
<s>
In	O
late	O
2009	O
,	O
IBM	O
announced	O
DB2	B-Application
pureScale	O
,	O
a	O
shared-disk	O
clustering	B-Architecture
scheme	O
for	O
DB2	B-Application
9.8	O
on	O
AIX	O
that	O
mimics	O
the	O
parallel	O
sysplex	O
implementation	O
behind	O
Db2	B-Application
data	O
sharing	O
on	O
the	O
mainframe	O
.	O
</s>
<s>
In	O
February	O
2008	O
,	O
Sybase	B-Application
released	O
its	O
Adaptive	B-Application
Server	I-Application
Enterprise	I-Application
,	O
Cluster	O
Edition	O
.	O
</s>
<s>
It	O
resembles	O
Oracle	B-Operating_System
RAC	I-Operating_System
in	O
its	O
shared-everything	O
design	O
.	O
</s>
<s>
Although	O
technically	O
not	O
shared-everything	O
,	O
Sybase	B-Application
also	O
provides	O
a	O
column-based	O
relational	O
database	O
focused	O
on	O
analytic	O
and	O
datawarehouse	O
applications	O
called	O
Sybase	B-Application
IQ	I-Application
that	O
can	O
be	O
configured	O
to	O
run	O
in	O
a	O
shared	O
disk	B-Device
mode	O
.	O
</s>
<s>
Cloud	O
Native	O
Databases	O
,	O
such	O
as	O
Amazon	O
Aurora	O
and	O
POLARDB	O
of	O
Alibaba	B-General_Concept
Cloud	I-General_Concept
,	O
are	O
implemented	O
with	O
"	O
shared-everything	O
"	O
architecture	O
on	O
top	O
of	O
cloud-based	O
distributed	O
file	O
system	O
.	O
</s>
<s>
Shared-nothing	B-Operating_System
architectures	I-Operating_System
share	O
neither	O
the	O
data	O
on	O
disk	B-Device
nor	O
the	O
data	O
in	O
memory	O
between	O
nodes	O
in	O
the	O
cluster	O
.	O
</s>
<s>
Competitive	O
products	O
offering	O
shared-nothing	B-Operating_System
architectures	I-Operating_System
include	O
:	O
</s>
<s>
Apache	B-Application
Cassandra	I-Application
,	O
wide	O
column	O
store	O
NoSQL	O
database	O
.	O
</s>
<s>
MongoDB	B-Application
,	O
document-oriented	O
database	O
.	O
</s>
