<s>
The	O
software	O
which	O
Oracle	B-Application
Corporation	I-Application
markets	O
as	O
Oracle	B-Application
Data	I-Application
Guard	I-Application
forms	O
an	O
extension	O
to	O
the	O
Oracle	B-General_Concept
relational	I-General_Concept
database	I-General_Concept
management	I-General_Concept
system	I-General_Concept
(	O
RDBMS	O
)	O
.	O
</s>
<s>
It	O
aids	O
in	O
establishing	O
and	O
maintaining	O
secondary	O
standby	O
databases	B-Application
as	O
alternative/supplementary	O
repositories	O
to	O
production	O
primary	O
databases	B-Application
.	O
</s>
<s>
Oracle	B-General_Concept
provides	O
both	O
graphical	B-Application
user	I-Application
interface	I-Application
(	O
GUI	B-Application
)	O
and	O
command-line	B-Application
(	O
CLI	O
)	O
tools	O
for	O
managing	O
Data	O
Guard	O
configurations	O
.	O
</s>
<s>
Oracle	B-Application
Corporation	I-Application
makes	O
Data	O
Guard	O
available	O
only	O
as	O
a	O
bundled	O
feature	O
included	O
within	O
its	O
"	O
Enterprise	O
Edition	O
"	O
of	O
the	O
Oracle	B-General_Concept
RDBMS	I-General_Concept
.	O
</s>
<s>
With	O
appropriately	O
set-up	O
Data	O
Guard	O
operations	O
,	O
DBAs	O
can	O
facilitate	O
failovers	B-General_Concept
or	O
switchovers	B-General_Concept
to	O
alternative	O
hosts	O
in	O
the	O
same	O
or	O
alternative	O
locations	O
.	O
</s>
<s>
For	O
the	O
purposes	O
of	O
Data	O
Guard	O
,	O
each	O
Oracle	B-General_Concept
database	I-General_Concept
functions	O
either	O
in	O
a	O
primary	O
database	O
role	O
or	O
in	O
a	O
standby	O
database	O
role	O
-	O
with	O
the	O
ability	O
to	O
transition	O
from	O
one	O
role	O
to	O
the	O
other	O
.	O
</s>
<s>
A	O
physical	O
standby	O
database	O
replicates	O
the	O
exact	O
contents	O
of	O
its	O
primary	O
database	O
across	O
the	O
Oracle	B-Application
Net	I-Application
network	B-Application
layer	I-Application
.	O
</s>
<s>
Physical	O
standby	O
databases	B-Application
can	O
function	O
either	O
in	O
managed-recovery	O
mode	O
or	O
in	O
read-only	O
mode	O
,	O
but	O
not	O
in	O
both	O
modes	O
at	O
the	O
same	O
time	O
(	O
unless	O
the	O
databases	B-Application
are	O
at	O
Oracle	B-General_Concept
Database	I-General_Concept
11.1	O
or	O
higher	O
and	O
the	O
Active	O
Data	O
Guard	O
option	O
is	O
licensed	O
-	O
see	O
below	O
)	O
.	O
</s>
<s>
Physical	O
standby	O
databases	B-Application
have	O
the	O
same	O
DBID	O
identifiers	O
as	O
their	O
primary	O
equivalents	O
.	O
</s>
<s>
Logical	O
standby	O
databases	B-Application
convert	O
the	O
redo	O
generated	O
at	O
the	O
primary	O
database	O
into	O
data	O
and	O
SQL	O
and	O
then	O
re-apply	O
those	O
SQL	O
transactions	O
on	O
the	O
logical	O
standby	O
.	O
</s>
<s>
Users	O
can	O
read	O
from	O
logical	O
standby	O
databases	B-Application
while	O
the	O
changes	O
are	O
being	O
applied	O
and	O
,	O
if	O
the	O
GUARD	O
is	O
set	O
to	O
STANDBY	O
(	O
ALTER	O
DATABASE	O
GUARD	O
STANDBY	O
;	O
)	O
,	O
write	O
to	O
tables	O
in	O
the	O
logical	O
standby	O
database	O
that	O
are	O
not	O
being	O
maintained	O
by	O
SQL	O
Apply	O
.	O
</s>
<s>
:	O
datatypes	O
BFILE	O
,	O
ROWID	O
,	O
and	O
UROWID	O
,	O
user-defined	O
TYPEs	O
,	O
multimedia	O
data	O
types	O
like	O
Oracle	B-General_Concept
Spatial	O
,	O
ORDDICOM	O
,	O
and	O
Oracle	B-General_Concept
Text	O
Collections	O
(	O
e.g.	O
</s>
<s>
The	O
"	O
Oracle	B-Application
Active	I-Application
Data	I-Application
Guard	I-Application
"	O
option	O
,	O
an	O
extra-cost	O
facility	O
,	O
extends	O
Oracle	B-Application
Data	I-Application
Guard	I-Application
functionality	O
in	O
Oracle	B-General_Concept
11g	I-General_Concept
configurations	O
.	O
</s>
<s>
LNS	O
(	O
log-write	O
network-server	O
)	O
and	O
ARCH	O
(	O
archiver	O
)	O
processes	O
running	O
on	O
the	O
primary	O
database	O
select	O
archived	O
redo	B-Application
logs	I-Application
and	O
send	O
them	O
to	O
the	O
standby-database	O
host	O
,	O
where	O
the	O
RFS	O
(	O
remote	O
file	O
server	O
)	O
background	O
process	O
within	O
the	O
Oracle	B-General_Concept
instance	O
performs	O
the	O
task	O
of	O
receiving	O
archived	O
redo	B-Application
logs	I-Application
originating	O
from	O
the	O
primary	O
database	O
and	O
writing	O
them	O
to	O
a	O
standby	O
redo	B-Application
log	I-Application
(	O
SRL	O
)	O
.	O
</s>
<s>
Alternatively	O
,	O
a	O
supplementary	O
mechanism	O
may	O
transfer	O
the	O
archived	O
redo	B-Application
logs	I-Application
.	O
</s>
<s>
Once	O
the	O
archived	O
redo	B-Application
logs	I-Application
have	O
arrived	O
on	O
the	O
standby	O
host	O
,	O
other	O
processes	O
-	O
such	O
as	O
an	O
ARCH	O
(	O
archiver	O
process	O
)	O
,	O
an	O
MRP	O
(	O
Managed	O
Recovery	O
Process	O
)	O
,	O
and/or	O
an	O
LSP	O
(	O
Logical	O
Standby	O
Process	O
)	O
-	O
may	O
set	O
about	O
applying	O
the	O
log	O
contents	O
to	O
the	O
standby	O
database	O
.	O
</s>
<s>
The	O
Data	O
Guard	O
Connection	O
process	O
(	O
DRCX	O
)	O
plays	O
a	O
role	O
in	O
transferring	O
data	O
between	O
databases	B-Application
.	O
</s>
<s>
Data	O
Guard	O
provides	O
high	O
availability	O
for	O
a	O
database	B-Application
system	I-Application
.	O
</s>
<s>
It	O
can	O
also	O
reduce	O
the	O
human	O
intervention	O
required	O
to	O
switch	O
between	O
databases	B-Application
at	O
disaster-recovery	B-General_Concept
(	O
"	O
failover	B-General_Concept
"	O
)	O
or	O
upgrade/maintenance	O
(	O
"	O
switchover	B-General_Concept
"	O
)	O
time	O
.	O
</s>
<s>
Through	O
the	O
use	O
of	O
standby	O
redo	B-Application
log	I-Application
files	I-Application
,	O
Data	O
Guard	O
can	O
minimize	O
data	O
loss	O
.	O
</s>
<s>
It	O
supports	O
heterogeneous	O
configurations	O
in	O
which	O
the	O
primary	O
and	O
standby	O
systems	O
may	O
have	O
different	O
CPU	O
architectures	O
,	O
operating	O
systems	O
(	O
for	O
example	O
,	O
Microsoft	O
Windows	O
and	O
Linux	O
)	O
,	O
operating-system	O
binaries	O
(	O
32-bit/64	O
-bit	O
)	O
,	O
or	O
Oracle	B-General_Concept
database	I-General_Concept
binaries	O
(	O
32-bit/64	O
-bit	O
)	O
.	O
</s>
<s>
If	O
the	O
network	O
link	O
connecting	O
primary	O
and	O
standby	O
is	O
over-subscribed	O
,	O
the	O
redo	B-Application
logs	I-Application
are	O
not	O
shipped	O
in	O
chronological	O
order	O
,	O
which	O
can	O
result	O
in	O
large	O
gaps	O
appearing	O
in	O
the	O
available	O
redo	O
at	O
the	O
standby	O
.	O
</s>
<s>
This	O
can	O
be	O
overcome	O
,	O
using	O
Oracle’	O
Active	O
Data	O
Guard	O
Farsync	O
technology	O
.	O
</s>
<s>
The	O
same	O
release	O
of	O
Oracle	B-General_Concept
Database	I-General_Concept
Enterprise	O
Edition	O
must	O
be	O
installed	O
on	O
the	O
primary	O
database	O
and	O
all	O
standby	O
databases	B-Application
,	O
except	O
during	O
rolling	O
database	O
upgrades	B-General_Concept
using	O
logical	O
standby	O
databases	B-Application
.	O
</s>
<s>
Oracle	B-Application
Data	I-Application
Guard	I-Application
is	O
available	O
only	O
as	O
a	O
feature	O
of	O
Oracle	B-General_Concept
Database	I-General_Concept
Enterprise	O
Edition	O
.	O
</s>
