In an Oracle database, tablespaces are fundamental to how data is organized and managed.
1. SYSTEM Tablespace
- Purpose: This is the most crucial tablespace. It houses the data dictionary, which contains metadata about the entire database.
This includes information about users, tables, indexes, and other database objects. - Key Points:
- Created automatically when the database is created.
- Cannot be dropped or renamed.
- Always online when the database is open.
- Should not be used to store user data.
2. SYSAUX Tablespace
- Purpose: An auxiliary tablespace to the SYSTEM tablespace.
It stores various system-related data, reducing the load on the SYSTEM tablespace. - Key Points:
- Created automatically when the database is created.
- Cannot be dropped or renamed.
- Created automatically when the database is created.
3. TEMP Tablespace
- Purpose: Used for temporary data that exists only for the duration of a session or transaction.
This includes: - Intermediate sort results
- Temporary tables and indexes
- Temporary LOBs (Large Objects)
- Key Points:
- Improves concurrency of sort operations that don't fit in memory.
- Enhances efficiency of space management during sorts.
- Improves concurrency of sort operations that don't fit in memory.
4. UNDO Tablespace
- Purpose: Stores undo information, which is crucial for transaction management.
It allows Oracle to: - Provide read consistency for queries.
- Roll back transactions that fail to commit.
- Key Points:
- Used when the database is in automatic undo management mode.
- Ensures data integrity and recoverability.
5. USERS Tablespace
- Purpose: The default tablespace for storing user objects and data. This is where you'll typically create your tables, indexes, and other schema objects.
- Key Points:
- Can be used to organize user data logically.
- Helps in managing disk space allocation for users.
Additional Tablespace Types
- Bigfile Tablespaces: These tablespaces contain a single, very large data file.
They simplify tablespace management and can significantly increase storage capacity. - Locally Managed Tablespaces: These tablespaces use bitmaps within the data files to manage free space, offering better performance and efficiency compared to dictionary-managed tablespaces.
Important Considerations
- Datafiles: Tablespaces are composed of one or more datafiles, which are the physical files that store the actual data?
- Extent Management: How free space is managed within a tablespace (locally managed or dictionary-managed)?
- Space Management: Techniques for allocating and managing space within tablespaces.
Understanding the different types of tablespaces and their purposes is essential for effectively managing an Oracle database. It allows you to organize data efficiently, optimize performance, and ensure data integrity.
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