Backup and Recovery overview, Instance and Media Recovery // Database Administration
Backup and Recovery Overview in Oracle Database
Backup and recovery are critical aspects of database administration, ensuring data integrity, availability, and resilience against failures. This overview will cover the fundamentals of backup and recovery in Oracle Database, including instance recovery and media recovery.
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1. Importance of Backup and Recovery
**Data Protection**: Safeguards against data loss due to hardware failures, user errors, or natural disasters.
**Business Continuity**: Ensures that operations can resume quickly after an outage.
**Regulatory Compliance**: Many industries require data retention and recovery processes to meet legal obligations.
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2. Types of Backups
#### 2.1. Physical Backups
**Cold Backup**: The database is shut down, and files are copied. This method ensures data consistency but requires downtime.
**Hot Backup**: The database remains open while files are copied. This allows for continuous availability but requires careful management to ensure consistency.
#### 2.2. Logical Backups
**Export/Import**: Use Oracle's Data Pump or the older `exp`/`imp` utilities to export data to a file and import it back into the database. This method captures logical data structures and can be used for migrating data between databases.
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3. Recovery Types
#### 3.1. Instance Recovery
**Definition**: Instance recovery occurs automatically when an Oracle instance crashes or is terminated unexpectedly. It ensures that the database is brought back to a consistent state.
**Process**:
1. **Redo Log Application**: Oracle applies changes from the redo logs to all committed transactions that were in the process of being written to data files.
2. **Undo Data Use**: Oracle uses undo segments to roll back any uncommitted transactions.
#### 3.2. Media Recovery
**Definition**: Media recovery is required when a data file becomes corrupted or lost. It restores the database to a consistent state using backups and redo logs.
**Types of Media Recovery**:
**Complete Recovery**: Restores the entire database to the most recent state using full backups and applying all necessary archived redo logs.
**Point-in-Time Recovery**: Restores the database to a specific moment using backups and redo logs, useful for recovering from user errors.
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4. Backup Strategies
#### 4.1. RMAN (Recovery Manager)
**Overview**: RMAN is Oracle's built-in tool for backup and recovery. It automates the backup process and manages backups efficiently.
**Advantages**:
Incremental backups: Only changes since the last backup are saved.
Cross-platform support: RMAN backups can be restored across different platforms.
Integration with the Oracle environment: Seamless management of backups, including validation and recovery.
#### 4.2. User-Managed Backups
**Manual Backups**: Administrators can manually copy data files, control files, and redo logs using operating system commands.
**Limitations**: Requires careful planning and is prone to human error; not as efficient as RMAN.
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5. Performing Backups
#### 5.1. Using RMAN
```sql
RMAN BACKUP DATABASE PLUS ARCHIVELOG;
```
This command backs up the entire database along with archived redo logs.
#### 5.2. User-Managed Backup Example
1. *Put the database in backup mode* (for hot backups):
```sql
ALTER DATABASE BEGIN BACKUP;
```
2. *Copy data files* using OS commands.
3. **End backup mode**:
```sql
ALTER DATABASE END BACKUP;
```
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6. Recovery Procedures
#### 6.1. Instance Recovery Process
1. **Startup the database**. Oracle automatically handles instance recovery.
2. *Review the alert log* for any issues during recovery.
#### 6.2. Media Recovery Process
1. *Restore the data files* from the backup to their original location.
2. *Recover the database* using RMAN or SQL commands.
**Using RMAN**:
```sql
RMAN RESTORE DATABASE;
RMAN RECOVER DATABASE;
```
3. **Open the database**:
```sql
ALTER DATABASE OPEN;
```
#### 6.3. Point-in-Time Recovery Example
1. **Restore the last backup**.
2. *Apply the necessary archived redo logs* up to the specified time.
```sql
RMAN RUN {
RESTORE DATABASE TO TIME "TO_DATE('YYYY-MM-DD HH24:MI:SS', 'YYYY-MM-DD HH24:MI:SS')";
RECOVER DATABASE;
}
```
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7. Best Practices for Backup and Recovery
1. **Regular Backup Schedule**: Implement a consistent backup strategy to ensure data is regularly backed up.
2. **Test Recovery Procedures**: Regularly test backup and recovery processes to ensure they work as expected.
3. **Use RMAN**: Leverage RMAN for efficient and reliable backup and recovery management.
4. **Monitor Backup Jobs**: Regularly check backup logs and alerts to address issues promptly.
5. **Implement Redundancy**: Store backups in multiple locations (on-site and off-site) to safeguard against data loss.
