Introduction to metadata of database instances - Data Management

Metadata is used for display and retrieval within the product. It provides the foundational information required for the automatic detection of sensitive data and for fine-grained permission control over objects such as databases, tables, fields, data rows, and programmable objects. Data Management (DMS) provides different metadata acquisition scopes and methods based on the control mode of the database instance.

Background information

Metadata, also known as a data dictionary, is data that describes the database itself. It includes information such as database names, database character sets, table names, table sizes, the number of table records, table character sets, table fields, table indexes, table descriptions, field types, field precision, and field descriptions. All this information is sourced from internal database objects, such as information_schema. Data points such as table size and row count may not be exact. This data should be used for order-of-magnitude reference only.

Acquisition scope and methods

Acquisition scope and method	Security Protection	Not Security Managed
Metadata acquisition scope	Acquires and stores all metadata for the database instance. For more information, see List of acquired metadata.	Acquires and stores only database-level information. Other metadata is loaded in real time after you log on.
Full metadata acquisition upon initial entry	Yes.	Yes.
Scheduled full acquisition	By default, the system automatically triggers acquisition for all instances under Security Protection within the tenant at 18:00 daily.	No.
On-demand incremental acquisition	Click the refresh button in the SQLConsole. Click the Refresh/Sync Dictionary button in the database instance list on the left side of the console home page. A DBA or administrator can also trigger an incremental acquisition in System Administration > Instance Management. For more information, see Sync metadata. Data Definition Language (DDL) changes made through DMS automatically trigger an incremental acquisition of the corresponding table metadata.	Click the refresh button in the SQLConsole. Click the Refresh/Sync Dictionary button in the database instance list on the left side of the console home page. A DBA or administrator can also trigger an incremental acquisition in System Administration > Instance Management. For more information, see Sync metadata.
Other	None.	When you log on, database information is acquired based on the permissions of the database account.

Use metadata

In addition to retrieval and permission management, you can export metadata using an OpenAPI. This is useful for tasks such as compliance audits. For more information about the OpenAPI documentation for metadata, see Database and table metadata.

Note

This feature is available only for instances under Security Protection.

List of acquired metadata

Object	MySQL protocol series①	PostgreSQL protocol series②	SQL Server	Oracle	MongoDB	Redis
Database	Name Character set	Name	Name	Name	None	Name
Table	Name Description Character set Number of rows Size	Name Description Number of rows Size	Name Description Number of rows Size	Name Description Number of rows Size	None	None
Field	Name Type Is nullable Length Precision Description	Name Type Is nullable Length Precision Description	Name Type Is nullable Length Precision Description	Name Type Is nullable Length Precision Description	None	None
Index	Name Type Index fields	Name Type Index fields	Name Type Index fields	Name Type Index fields	Name Index fields	None
Programmable object	Name Type	Name Type	Name Type	None	None	None
Schema	None	Name	None	None	None	None
Collection	None	None	None	None	Name	None
Key	None	None	None	None	None	Name Type

Note

①: MySQL, PolarDB for MySQL, PolarDB distributed version, AnalyticDB for MySQL, DLA, ClickHouse, OceanBase MySQL mode, and MariaDB.

②: PostgreSQL, PolarDB for PostgreSQL (Compatible with Oracle), PolarDB for PostgreSQL, AnalyticDB for PostgreSQL, and OceanBase Oracle mode.