Oracle Dataguard:
1. What are different protection modes in dataguard?
There are three modes.
a.
MAXIMUM PROTECTION
This mode
provides maximum protection. It guarantees zero data loss. In this mode the
redo/transaction data must be written to both primary redo log and standby redo
log. For any reason(mostly N/W issue) if it is unable to write to standby, Then
primary will get shutdown.
b.
MAXIMUM AVAILABILITY:
It provides
the highest level of data protection that is possible without affecting the
availability of the primary database.Transactions are not allowed to commit
until all redo data are written to the online redo logs and propagated to at
least one synchronized secondary database. If for any reason, the primary
database cannot propagate its redo stream to one secondary database, the
primary will NOT shutdown and operates as it it were in maximum performance mode
until issues are fixed.
c.
MAXIMUM PERFORMANCE:(default one)
This is the default protection mode. With this protection mode, a transaction is committed as soon as the redo data needed to recover the transaction is written to the local (online) redo log.
2. What are different types of dataguard and their
difference?
There are two types of dataguard setups. PHYSICAL and LOGICAL.
PHYSICAL STANDBY:
A physical standby database is an exact, block-for-block copy of a primary database. A physical standby is maintained as an exact copy through a process called REDO APPLY, in which redo data received from a primary database is continuously applied to a physical standby database using the database recovery mechanisms. So it will be always in sync with primary.
This Standby database can be opened in read only mode( knows as ACTIVE DATA GUARD), for reporting purpose. Most of the corporations use physical standby for dataguard configuration.
LOGICAL STANDBY:
The logical standby
database is kept synchronized with the primary database through SQL APPLY,
which transforms the data in the redo received
from the primary database into SQL statements and then executes the SQL
statements on the standby database. So it contains same logical information as
that of production , but physical structure of data can be different.
3. What is the process to apply a psu patch in dataguard
setup.
- Make sure lag between primary and standby is zero.
- Cancel the recovery (MRP) on standby.
- Shutdown standby db and listener.
- Apply patch to binary using opatch apply command.
- Once patch applied to binary , startup the listener and standby in mount stage or OPEN(if active dataguard).
- Now shutdown primary db and listener.
- Apply patch to binary using opatch apply command.
- Once patch applied to binary , startup the listener and prim db in mount OPEN(if active dataguard).
- Start the MRP recovery process on standby.
Below are the benefit of using active dataguard.
Reporting queries can be offloaded to standby database.
Physical block corruptions are repaired automatically either at primary or physical standby database.
RMAN backups can be initiated from standby , instead of primary which will reduce cpu load from primary.
NOTE – To use active dataguard, you need additional license from oracle.
