Recovery Strategies in Oracle Database
Key Concepts
Recovery strategies in Oracle Database are essential for ensuring data integrity and availability. Understanding the following key concepts is crucial for effective recovery management:
1. Physical Backup
Physical backups involve copying the physical files that make up the database. This includes data files, control files, and redo log files. Physical backups are typically performed using Oracle's Recovery Manager (RMAN).
Example:
Creating a full physical backup using RMAN:
RMAN> BACKUP DATABASE PLUS ARCHIVELOG;
2. Logical Backup
Logical backups involve exporting the logical structure and data of the database using tools like Oracle Data Pump or the older Export utility. Logical backups are useful for migrating data between databases.
Example:
Exporting a schema using Oracle Data Pump:
expdp system/password DIRECTORY=dpump_dir DUMPFILE=schema.dmp SCHEMAS=hr;
3. Full Database Recovery
Full database recovery involves restoring the entire database to a consistent state using backups and redo logs. This is typically done after a catastrophic failure.
Example:
Performing a full database recovery using RMAN:
RMAN> RECOVER DATABASE;
4. Point-in-Time Recovery (PITR)
Point-in-Time Recovery allows the database to be restored to a specific point in time, typically using archived redo logs. This is useful for recovering from logical data corruption or user errors.
Example:
Performing a Point-in-Time Recovery to a specific timestamp:
RMAN> RECOVER DATABASE UNTIL TIME 'YYYY-MM-DD HH24:MI:SS';
5. Incremental Backup
Incremental backups capture only the changes made to the database since the last backup. This reduces backup time and storage requirements compared to full backups.
Example:
Creating an incremental backup using RMAN:
RMAN> BACKUP INCREMENTAL LEVEL 1 DATABASE;
6. Archive Log Mode
Archive Log Mode ensures that redo logs are archived before they are reused. This is essential for performing Point-in-Time Recovery and maintaining data integrity.
Example:
Enabling Archive Log Mode:
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER DATABASE ARCHIVELOG;
ALTER DATABASE OPEN;
7. Flashback Database
Flashback Database allows the database to be rolled back to a previous state without performing a full recovery. This is useful for quickly recovering from user errors or logical corruption.
Example:
Using Flashback Database to revert to a previous state:
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
FLASHBACK DATABASE TO TIMESTAMP TO_TIMESTAMP('YYYY-MM-DD HH24:MI:SS', 'YYYY-MM-DD HH24:MI:SS');
ALTER DATABASE OPEN RESETLOGS;
8. Flashback Table
Flashback Table allows individual tables to be restored to a previous state without affecting the rest of the database. This is useful for recovering from accidental data modifications.
Example:
Using Flashback Table to restore a table to a previous state:
FLASHBACK TABLE Employees TO TIMESTAMP TO_TIMESTAMP('YYYY-MM-DD HH24:MI:SS', 'YYYY-MM-DD HH24:MI:SS');
9. Flashback Drop
Flashback Drop allows dropped tables to be recovered from the recycle bin. This is useful for recovering from accidental table drops.
Example:
Using Flashback Drop to recover a dropped table:
FLASHBACK TABLE Employees TO BEFORE DROP;
10. Flashback Query
Flashback Query allows querying data as it existed at a specific point in time. This is useful for auditing and troubleshooting data changes.
Example:
Using Flashback Query to view data as it existed at a specific timestamp:
SELECT * FROM Employees AS OF TIMESTAMP TO_TIMESTAMP('YYYY-MM-DD HH24:MI:SS', 'YYYY-MM-DD HH24:MI:SS');
11. Data Guard
Data Guard provides a high availability and disaster recovery solution by maintaining a standby database that is synchronized with the primary database. This ensures minimal downtime in case of a failure.
Example:
Configuring Data Guard with a physical standby database:
CREATE STANDBY DATABASE;
12. Active Data Guard
Active Data Guard extends Data Guard by allowing the standby database to be opened for read-only access. This allows for reporting and other read-only operations to be performed on the standby database.
Example:
Enabling Active Data Guard:
ALTER DATABASE OPEN READ ONLY;
13. Fast Recovery Area (FRA)
The Fast Recovery Area is a disk-based storage area used for storing backup files, archived redo logs, and other recovery-related files. It simplifies the management of recovery files.
Example:
Configuring the Fast Recovery Area:
ALTER SYSTEM SET DB_RECOVERY_FILE_DEST_SIZE = 10G;
ALTER SYSTEM SET DB_RECOVERY_FILE_DEST = '/u01/fra';
14. Recovery Catalog
The Recovery Catalog is a database schema used by RMAN to store metadata about backups and recovery operations. It provides a centralized repository for managing recovery information.
Example:
Creating a Recovery Catalog:
RMAN> CREATE CATALOG;
15. Standby Database
A standby database is a replica of the primary database that is kept synchronized using redo logs. It provides a failover solution in case of a primary database failure.
Example:
Creating a standby database:
CREATE STANDBY DATABASE;
16. Log Shipping
Log Shipping involves shipping redo logs from the primary database to the standby database for application. This ensures that the standby database remains synchronized with the primary database.
Example:
Configuring Log Shipping:
ALTER SYSTEM SET LOG_ARCHIVE_DEST_2 = 'SERVICE=standby_db';