What is a tablespace?
In Oracle, a tablespace is a logical storage container used to group and allocate storage space for database objects like tables, indexes, partitions, etc. It’s a fundamental component of Oracle’s architecture and provides a way to manage and allocate disk space for storing data.
Tablespaces allow for the organization and segregation of database objects, and they provide several advantages:
- Storage Management: Tablespaces help manage the physical storage of database objects separately. This segregation enables different storage parameters, such as allocation sizes, extent management, and storage characteristics.
- Performance Optimization: By assigning specific tablespaces to particular types of data or objects, performance can be optimized. For instance, frequently accessed tables or indexes can be stored in tablespaces on faster storage devices or disks.
- Backup and Recovery: Tablespaces can be backed up or restored independently, allowing for more granular backup strategies. This means that in case of a failure, only specific tablespaces might need to be recovered, reducing downtime.
- Space Allocation: They provide a way to control and allocate space to different users or segments of the database, which aids in efficient space management.
Oracle offers various types of tablespaces, including:
- System Tablespace: Contains the data dictionary and other system-related information necessary for the functioning of the database.
- User/Non-system Tablespaces: Created by users to store their data objects like tables, indexes, etc.
- Temporary Tablespaces: Used for sorting and joining operations, and for storing temporary data.
- Undo Tablespace: Manages rollback segments, which are essential for maintaining data consistency in case of a rollback operation.
Each tablespace consists of one or more data files or data file segments, which are physical files on the disk where the actual data is stored.
Overall, tablespaces play a crucial role in the management, organization, and performance optimization of an Oracle database by providing a structured way to store and manage its data.
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What is a SYSTEM tablespace and when it is created?
The SYSTEM tablespace in Oracle is a fundamental part of the database. It contains the core data dictionary, which consists of metadata essential for the functioning of the entire database. This metadata includes information about the database’s structure, objects, users, privileges, and much more.
The SYSTEM tablespace is created automatically when you create an Oracle database. During the database creation process, Oracle creates the SYSTEM tablespace as the default tablespace for the database. It stores the data dictionary tables and other important information required by the Oracle database to function properly.
Key points about the SYSTEM tablespace:
- Automatically Created: It is created by Oracle as part of the database creation process.
- Critical System Data: Contains the data dictionary, which is crucial for the database’s operation.
- Default Tablespace: When no other tablespace is specified for an object’s storage, the SYSTEM tablespace is often used as the default, though this isn’t always recommended due to potential issues related to space management and performance.
- Storage Management: As with other tablespaces, administrators can manage the storage parameters, such as size, extent management, and other characteristics, to ensure the smooth operation of the database.
It’s important to note that Oracle strongly advises against storing user data in the SYSTEM tablespace. Mixing user data with system data can lead to potential issues with database management, maintenance, and performance.
The separation of user data into separate tablespaces helps in better management, performance optimization, and ease of maintenance of the Oracle database. Administrators often create additional tablespaces dedicated to user data, indexes, temporary data, etc., keeping the SYSTEM tablespace primarily for the system-related metadata.