Archivelog | Noarchivelog   «Prev  Next»
Lesson 1

Archivelog and Noarchivelog Overview

Managing your databases requires some fundamental decisions. An important decision is what type of backup you will perform, either physical or logical. We will introduce a discussion on physical and logical backups in this module. We will reserve further discussion on logical backups for the third course in this series when we talk about using the Export/Import utilities. Instead we will focus on physical backups of our database.
In particular, we will start to discuss operating our database in noarchivelog and archivelog mode. Our options for backup and recovery of a database in noarchivelog mode are very limited and will be addressed in this module. We will also discuss archivelog mode in more detail in subsequent modules. We will investigate backup and recovery strategies based on the use of archivelog mode in the third part of this series.
By the end of this module, you should be familiar with the following:
  1. The differences between physical and logical backups
  2. The differences between online and offline backups
  3. The differences between archivelog and noarchivelog mode
  4. Operating a database in noarchivelog mode
  5. Configuring a database for archivelog mode and automatic archiving
  6. Configuring a database for duplex archivelog mode
By the end of this module you will be able to backup and restore your database when using noarchivelog mode. So let’s get started so that we can backup our database.

How does one determine whether Physical or Logical backups should occur in Oracle?

When deciding between physical and logical backups in Oracle, the decision hinges on various factors, including the specific requirements of the database, the intended use of the backups, the flexibility needed in recovery operations, and the database's size and complexity.

Physical Backups:

Physical backups consist of the files that store the database data, such as datafiles, control files, and archived redo logs. They are a byte-for-byte copy of the database and can be performed while the database is online (hot backup) or offline (cold backup).
  • Use Case: Physical backups are crucial for disaster recovery scenarios. They are suitable when the requirement is to restore the entire database or to perform point-in-time recoveries.
  • Advantages: Physical backups are typically faster to restore because they involve copying files directly back to their locations. They are comprehensive and include the entire database, ensuring no components are missed.
  • Disadvantages: These backups can be large, as they include the entire database, and they are less flexible because they do not allow for

Logical Backups:

Logical backups contain the logical data (such as tables, stored procedures, and other schema objects) extracted using tools like Oracle's Data Pump (expdp and impdp) or the older export/import utilities. These backups are in the form of SQL statements or proprietary binary format.
  • Use Case: Logical backups are beneficial when migrating data between databases, between different database versions, or when you need to recover specific objects.
  • Advantages: They provide the flexibility to recover individual objects and can be used to move data across different database structures or versions. Logical backups are also usually smaller in size than physical backups.
  • Disadvantages: The restoration process can be slower because the data needs to be re-inserted through SQL statements. They are not suitable for complete disaster recovery, as they do not include system-related files.

Determining Factors:

  1. Recovery Requirements: If complete disaster recovery is the goal, physical backups are necessary. For more selective data recovery or migration, logical backups are more suitable.
  2. Database Downtime: Physical backups can be done while the database is up and running, whereas logical backups may sometimes require downtime, depending on the method used and the database activity.
  3. Database Size: For large databases, physical backups are often more practical. Logical backups can become impractical due to the time and space required to manage the data export and import.
  4. Flexibility and Portability: Logical backups offer more flexibility for partial recovery and are portable between different architectures and database versions.
  5. Backup Window: The available time for performing backups may influence the choice. Physical backups can be integrated with media management solutions for speed and efficiency.
  6. Resource Utilization: Logical backups are generally more resource-intensive than physical backups, as they require more CPU and I/O to export and import data.
  7. Data Specificity: If the backup strategy involves cloning specific sets of data for development or testing purposes, logical backups may be more appropriate.

The choice between physical and logical backups is often not mutually exclusive. Many organizations implement both as part of a comprehensive backup strategy, using physical backups for disaster recovery and logical backups for data portability and object-level recovery. The decision should be based on a thorough assessment of recovery objectives, resources, and operational constraints, aligned with the organization's overall data protection policy.
The next lesson is about physical and logical backups.