Metadata describes a database. Metadata is also called a data dictionary. Metadata includes the database name, database character set, table names, table sizes, the number of rows in each table, the character set of each table, table columns, table indexes, the description of each table, the type of each column, the precision of the columns, and the description of the columns. Data Management (DMS) collects metadata from databases such as the
information_schema database. The collected metadata may not be accurate and is used only for reference.
Collection scopes and methods
|Collection scope and method||Security Collaboration||Stable Change and Flexible Management|
|Metadata collection scope||DMS collects and stores all metadata of an instance. For more information, see The collected metadata list.||DMS collects and stores all metadata of a database. Other metadata is loaded in real time after logon.|
|Whether to trigger full metadata collection when a database is added to DMS||Yes, full metadata collection is triggered when a database is added to DMS.||Yes, full metadata collection is triggered when a database is added to DMS.|
|Full metadata collection at specified points in time||By default, DMS collects metadata of all instances of a tenant at six points in time each day.
Note DMS synchronizes the metadata every four hours at 02:00:00, 06:00:00, 10:00:00, 14:00:00, 18:00:00, and 22:00:00.
|Full metadata collection at specified points in time is not supported.|
|On-demand incremental metadata collection||
|Others||None.||When you log on to a database, DMS collects information about the database based on the permissions of the account that you use to log on.|
Metadata can be used to retrieve data and manage permissions. Metadata can be exported by calling API operations to provide support for operations, such as compliance audit.
You can export only metadata of instances in Security Collaboration mode by calling API operations.
The following table lists topics of API operations that are related to metadata.
|GetDatabase||Queries the details of a database.|
|ListColumns||You can call this operation to query the column information of a specified table.|
|ListIndexes||You can call this operation to return information about table indexes.|
|GetLogicDatabase||Call the GetLogicDatabase operation to query the details about a logical database.|
|ListDatabases||You can call this operation to query detailed information of databases in a specified instance.|
|ListLogicDatabases||Call ListLogicDatabases returns logical database details List|
|ListLogicTables||You can call this ListLogicTables to query detailed information of logical tables in a specified logical database.|
|SearchDatabase||You can call this operation to query the information of a database.|
|SearchTable||You can call this operation to search the table details list.|
|ListTables||You can call this operation to query details about tables in a database.|
|SyncDatabaseMeta||Call the SyncDatabaseMeta to synchronize dictionary metadata from databases.|
|SyncInstanceMeta||Call the SyncInstanceMeta to synchronize the metadata of all database dictionaries under the specified instance.|
|Object||MySQL series ①||PostgreSQL series ②||Native SQL Server and ApsaraDB RDS for SQL Server||Oracle||Native MongoDB and ApsaraDB RDS for MongoDB||Native Redis and ApsaraDB RDS for Redis|
①: Native MySQL, PolarDB for MySQL, PolarDB-X, AnalyticDB for MySQL, Data Lake Analytics (DLA), ClickHouse, ApsaraDB OceanBase for MySQL, native MariaDB, and ApsaraDB RDS for MariaDB.
②: Native PostgreSQL, PolarDB-O, PolarDB for PostgreSQL, AnalyticDB for PostgreSQL, ApsaraDB OceanBase for Oracle, and ApsaraDB RDS for PPAS.