Overview of System Catalogs and System Views

System catalogs are used by GaussDB(DWS) to store structure metadata. They are a core component the GaussDB(DWS) database system and provide control information for the database system. These system catalogs contain cluster installation information and information about various queries and processes in GaussDB(DWS). You can collect information about the database by querying the system catalog.

System views provide ways to query system catalogs and internal database status. If some columns in one or more tables in a database are frequently searched for, an administrator can define a view for these columns, and then users can directly access these columns in the view without entering search criteria. A view is different from a basic table. It is only a virtual object rather than a physical one. A database only stores the definition of a view and does not store its data. The data is still stored in the original base table. If data in the base table changes, the data in the view changes accordingly. In this sense, a view is like a window through which users can know their interested data and data changes in the database. A view is triggered every time it is referenced.

In separation of duty, non-administrators have no permission to view system catalogs and views. In other scenarios, system catalogs and views are either visible only to administrators or visible to all users. Some of the following system catalogs and views have marked the need of administrator permissions. They are accessible only to administrators.

• Do not add, delete, or modify system catalogs or system views. Manual modification or damage to system catalogs or system views may cause system information inconsistency, system control exceptions, or even cluster unavailability.
• System catalogs do not support toast and cannot be stored across pages. The size of a page is 8 KB, and the length of each field in the system catalog must be less than 8 KB.