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Oracle – 38 – System Tables

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In Oracle, system tables, also known as data dictionary tables or catalog tables, are a set of special tables that store metadata and information about the database itself. These tables are maintained by the Oracle database system and are used to manage and track various aspects of the database’s structure, objects, and user access. Here’s a brief description of Oracle’s system tables:

1. Purpose:

  • System tables serve as a repository of metadata and information about the database’s schema, objects, constraints, privileges, and more. They provide a structured way to query and manage the database’s internal details.

2. Data Dictionary Views:

  • In Oracle, system tables are exposed to users through data dictionary views. These views present the data stored in system tables in a user-friendly and accessible format.
  • Common data dictionary views include DBA_TABLES, DBA_COLUMNS, DBA_CONSTRAINTS, DBA_USERS, and many others. The prefix “DBA” indicates that these views provide access to all objects in the database.

3. Object Information:

  • System tables and data dictionary views contain information about database objects such as tables, views, indexes, sequences, procedures, functions, and triggers. This information includes object names, owner/schema, creation dates, and more.

4. User Privileges:

  • Information about user privileges and roles is stored in system tables. DBAs can query these tables to determine which users have specific privileges on database objects.

5. System Configuration:

  • System tables hold details about the database’s configuration settings, initialization parameters, and storage structures. They help DBAs monitor and configure the database environment.

6. Data Integrity and Constraints:

  • Information about table constraints, such as primary keys, unique constraints, foreign keys, and check constraints, is stored in system tables. These tables ensure data integrity and enforce rules on database objects.

7. User Information:

  • System tables store user-related information, including usernames, passwords (encrypted), roles, and profiles. This data is crucial for user management and security.

8. Dynamic Performance Views:

  • In addition to static system tables, Oracle provides dynamic performance views (e.g., V$SESSION, V$SQL) that contain real-time information about the database’s performance and status.

9. Access Control:

  • Access to system tables and data dictionary views is controlled through database privileges. Typically, only users with elevated privileges (e.g., DBAs) can query these tables.

10. Data Dictionary Caching: –

  • Oracle employs data dictionary caching mechanisms to improve performance. This means that the information in system tables may not always reflect real-time changes to the database structure. Refreshing the data dictionary views may be necessary to see the most up-to-date information.

System tables and data dictionary views play a crucial role in Oracle database administration, development, and troubleshooting. They provide a structured way to access essential information about the database, objects, users, and configuration settings. DBAs and developers use these tables and views extensively to monitor, manage, and optimize the database environment.