DB_ULTRA_SAFE is a
new parameter introduced with Oracle 11gR1, and a fantastic new GEM for High
Availability, that using Data Guard to configure on both the primary and
standby will trigger the most comprehensive data corruption prevention and
detection (and repair on 11gR2, see **) tool in the market.
** Starting in Oracle Database 11g Release 2 (11.2), the
primary database automatically attempts to repair the corrupted block in real
time by fetching a good version of the same block from a physical standby
database.
Speaking simple, what this new functionality will do is
use your Standby Database as a backup to correct automatically any data
corruption on your primary database and vice-versa (again on 11.2).
The DB_ULTRA_SAFE
initialization parameter also controls other data protection behavior in Oracle
Database, such as requiring ASM to perform sequential mirror write I/Os.
You basically need to understand that when setting DB_ULTRA_SAFE it will control the
behaviour of DB_BLOCK_CHECKING, DB_BLOCK_CHECKSUM, or DB_LOST_WRITE_PROTECT
parameters for you, which mean:
|
When you set
DB_ULTRA_SAFE to
|
Then the following
parameters…
|
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DATA_AND_INDEX
(recommended by Oracle)
|
|
|
DATA_ONLY
|
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Lets’ Check all the parameters affected by DB_ULTRA_SAFE:
·
DB_BLOCK_CHECKING
(Introduced with Oracle 8.1.6) prevents memory and data corruptions, but it
incurs some performance overhead on every block change.
·
DB_BLOCK_CHECKSUM (Introduced
with Oracle 8.1.6) detects redo and data block corruptions and detect
corruptions on the primary database and protect the standby database. This
parameter requires minimal CPU resources.
·
DB_LOST_WRITE_PROTECT
(also introduced with 11gR1) enable or disable a physical standby database to
detect lost write corruptions on both the primary and physical standby
database.
Important: if you explicitly set the DB_BLOCK_CHECKING, DB_BLOCK_CHECKSUM, or DB_LOST_WRITE_PROTECT
parameters in the initialization parameter file, then the DB_ULTRA_SAFE
parameter has no effect and no changes are made to the parameter values. Thus,
if you specify the DB_ULTRA_SAFE
parameter, do not explicitly set these underlying parameters.
To activate it, all you need to do is follow the
following steps:
On the Primary Database:
1.
Set
the DB_ULTRA_SAFE=DATA_AND_INDEX initialization parameter using:
2.
SQL>
alter system set db_ultra_safe=dta_and_index scope=spfile;
3.
SQL>
shutdown immediate (Shutdown your Database)
4.
SQL>
startup (This will start your primary Database using your new parameter set in
the SPFILE previously)
On the Physical Standby Database:
1.
Set
the DB_ULTRA_SAFE=DATA_AND_INDEX initialization parameter using:
2.
SQL>
alter system set db_ultra_safe=dta_and_index scope=spfile;
3.
SQL>
startup nomount
4.
SQL>
alter database mount standby database;
5.
SQL>
alter database recover managed standby database disconnect from session;
If you are using your Standby Database on Read Only mode
you also need to run the follow commands on your Physical Standby DB:
1.
SQL>
alter database recover managed standby database cancel;
2.
SQL>
alter database open read only;
If you decide to change later the Read Only Standby to
Standby again, you just will need to run the following command:
1.
SQL>
alter database recover managed standby database disconnect from session;
Hoping this information could help you in the future,
by Francisco Munoz Alvarez
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