Oracle Data Guard provides several key benefits: continuous database service during disasters or data failures, complete data protection against corruptions and loss, and offloading of queries and backups from primary systems. It uses redo transport to transfer redo logs from a primary database to one or more standby databases, and log apply to maintain synchronization. Different protection modes like maximum protection or maximum performance allow balancing data protection against primary performance.

1. Oracle10g Data Guard
Overview

2. Objectives
• Explain the benefits of Data Guard and why we
might use it
• Describe the basic components of Oracle Data
Guard

3. Benefits of Oracle Data Guard
• Configure the system to meet business protection
and recovery requirements
• Continuous service through a disaster or crippling
data failure
• Complete data protection against corruptions and
data loss
• Reduce overhead on primary systems by
offloading:
– adhoc queries
– reporting
– backups
• Centralized management (Data Guard Broker, Data
Guard Manager via Enterprise Manager)

4. Data Loss Causes…
Hardware & System Error 44%
Human Error 32%
Software Corruption 14%
Computer Viruses 7%
Natural Disasters 3%
* Protect Data 2006

5. What is Data Guard?
Primary Standby
Database Database
Redo
Oracle Net
Database Database Copy
Oracle® Data Guard Concepts and Administration 10g Release 2 (10.2)
“Ch. 1 Introduction to Oracle Data Guard “

7. Standby Databases
There are two types of standby databases:
1. Physical standby database
2. Logical standby database

8. Data Guard Services
There are three types of services provided
between the Primary and Standby databases:
1. Redo Transport: (2 types: Archival or Real-Time)
• Controls the transfer of redo data from the primary
database to the standby database.
2. Log Apply: (2 types: Redo Apply or SQL Apply)
• Applies redo data on the standby database to maintain
synchronization with the primary database.
3. Role Transitions: (2 types: Switchover or Failover)
• Change the role of a database:
SWITCHOVER: standby to primary + primary to standby
FAILOVER: standby to primary

9. Data Guard Services
Redo Transport
Redo transport services perform the following
tasks:
• Transmits redo data from the primary to one
or more standbys (9 max*) using ARCH or
LGWR (LNSn)
• Enforces the database protection mode
• Automatically detects missing or corrupted
archived redo log files on the standby and
retrieves replacement archived redo log files
from the primary, or another standby database
i.e.: “GAP” RESOLUTION
• Archival or Real-Time

10. Data Guard Services
No Standby – No REDO Transport
Primary
Database
Transactions
LGWR
Online
Redo Log Files
ARC0
Archived
Redo Log Files

11. Data Guard Services
Redo Transport (Archival)
Primary Physical
Database Standby
Transactions Database
LGWR RFS MSRP
Archival
Transport
Online
Redo
Redo Log Files
Apply
ARC0 ARC1 ARC0
Archived
Redo Log Files
Archived
Redo Log Files

12. Data Guard Services
Redo Transport (Real-Time)
Primary Logical
Database Standby
Transactions Database
LGWR LSN0 RFS LGWR LSP
Online Standby
SQL
Redo Log Files Redo Log Files
Real-Time Apply
Transport (Required)
ARC0 ARC0
Archived
Redo Log Files
Archived
Redo Log Files

13. Data Guard Services
Redo Transport Configuration
Redo transport is configured via parameters:
LOG_ARCHIVE_DEST_n (n = { 1..10 })
• One destination must be LOCAL and must be MANDATORY.
This destination, usually n = 1, is always archived first when
using ARCH for redo transport
• Destination n = 10 is the default FLASHBACK RECOVERY
area.
LOG_ARCHIVE_DEST_STATE_n
• Allows one to ENABLE, DEFER, or RESET a specific
destination
STANDBY_ARCHIVE_DEST (standby only)
• If no LOG_ARCHIVE_DEST_n locations specified then
provides default location for archived redo logs

14. Data Guard Services
Log Apply (Redo Apply)
For physical standby databases, Data Guard uses Redo Apply
technology, which applies redo data on the standby database
using standard recovery techniques of an Oracle database.
I.e. Block-for-block, byte-for-byte, bit-for-bit identical to primary.

15. Data Guard Services
Log Apply (SQL Apply)
For logical standby databases, Data Guard uses SQL Apply
technology, which transforms the received redo data into SQL
statements and then executes the generated SQL statements on
the logical standby database.
I.e. Use Log Mining to extract the redo, transform the redo into SQL
statements, then execute the SQL statements against the logical
standby.

16. Role Transitions
Switchover and Failover
• Not automatically invoked (but can be…)
• Switchover
– Planned role reversal
– Used for OS or hardware maintenance
• Failover
– Unplanned role reversal
– Use in an emergency
– Minimal or zero data loss depending on choice of
data protection mode

17. Data Protection Modes
Maximum Protection
• Ensures that no data loss will occur if the primary
database fails.
• Redo needed to recover each transaction must be
written to both the local online redo log and to the
standby redo log on at least one standby database
before the transaction commits.
• If a fault prevents the primary database from
writing its redo stream to the standby redo log of
at least one transactionally-consistent standby
database, the primary database shuts down.

19. Data Protection Modes
Maximum Performance
• Default. Provides highest level of data protection
possible without affecting the performance of the
primary database.
• Transactions may commit as soon as the redo
data needed to recover them transaction is written
to the primary’s online redo log.
• Redo data stream written asynchronously to at
least one standby database.
• If sufficient bandwidth exists, provides a level of
data protection that approaches that of maximum
availability mode with minimal impact on primary
database performance.

20. Setting the Protection Mode
To set up redo transport services and specify a level of data
protection for the Data Guard configuration, perform the following
steps.
Step 1: Configure the LOG_ARCHIVE_DEST_n parameters on the
primary database.
Maximum Maximum Maximum
Protection Availability Performance
Redo archival process LGWR LGWR LGWR or ARCH
Network Transmission SYNC SYNC SYNC or ASYNC (LGWR)
Mode SYNC (ARCH)
Disk Write Option AFFIRM AFFIRM AFFIRM or NOAFFIRM
Standby Redo Log Yes Yes No but recommended
Required?

21. Setting the Protection Mode
Step 1: Bounce the primary database:
SQL> SHUTDOWN IMMEDIATE;
SQL> STARTUP MOUNT;
* If RAC, shutdown all instances, restart/mount one instance.
Step 2: Set the mode:
SQL> ALTER DATABASE SET STANDBY DATABASE TO PROTECTION MODE;
Step 3: Open the Primary Database:
SQL> ALTER DATABASE OPEN;
Step 4: Confirm LOG_ARCHIVE_DEST_n parameter(s) on Standby
Database:
SQL> SHOW PARAMETER log_archive_dest_
Step 5: Confirm configuration:
SQL> SELECT PROTECTION_MODE, PROTECTION_LEVEL FROM V$DATABASE;

22. Summary
In this lesson you should have learned:
• Benefits of Data Guard and why we might use it
• Basic components of Oracle Data Guard