Migrate data between OceanBase databases of the same tenant type

This topic describes how to use OceanBase Migration Service (OMS) to migrate data between OceanBase databases of the same tenant type.

Background information

You can create a data migration task in the OMS console to seamlessly migrate the existing business data and incremental data from a source OceanBase database to a target OceanBase database of the same type through schema migration, full migration, and incremental synchronization.

Prerequisites

• You have created the corresponding schema in the target OceanBase database.

• You have created dedicated database users for the source and target OceanBase databases for the data migration task and granted corresponding privileges to these users. For more information, see Create a database user.

• If you want to migrate a table without a primary key, you need to create users and grant privileges to them as needed before you execute the data migration task. For more information, see Create the __oceanbase_inner_drc_user user.

  Notice

  If the version of OceanBase Database is earlier than V2.2.30, OMS does not support the migration of tables without primary keys.

Limitations

• Limitations on the source database

  Do not perform DDL operations for database or schema changes during the schema migration and full migration phases. Otherwise, the data migration task may be interrupted.

• Data migration is supported only between databases of the same type in OceanBase Database.

  Data can be migrated from the MySQL compatible mode of OceanBase Database to the MySQL compatible mode, or from the Oracle compatible mode of OceanBase Database to the Oracle compatible mode.

• In the incremental synchronization scenario, if useTargetIndex = false, and the target database uses the BINARY type as the primary key or unique key, the source data length does not equal the length of the BINARY type in the target database, the UPDATE or DELETE operation cannot match the data, and there is a risk of data quality.

• Data sources and user accounts must be globally unique in OMS.

• OMS only supports migrating databases, tables, and column objects with ASCII-compliant names that do not contain special characters (spaces, line breaks, or .|"'`()=;/&\).

• OMS does not support the migration of data from OceanBase Database V1.4.x to OceanBase Database V4.x.

• The full migration will fail if there are temporary tables in the MySQL compatible mode of OceanBase Database V4.0.0 or earlier.

• OMS does not support a primary key that contains the FLOAT or DOUBLE type.

• If the source is OceanBase Database V1.4.79, the target must be V2.2.77 or later. If the source is OceanBase Database V2.1.0 or later, the source and target can be of different OceanBase Database versions.

• In OMS V3.2.0 and later, a single migration task supports the migration of both tables with primary keys and tables without primary keys.

• OMS does not support triggers in the target database. If triggers exist in the target database, the data migration may fail.

• OMS does not support an OceanBase standby database as the source.

Considerations

• For OceanBase Database V4.x, we recommend that you enable archive logs. With archive logs enabled, OMS can still achieve incremental synchronization capability by consuming archive logs even if Clogs are recycled. For more information about how to enable archive logs, see Archive logs.

• If the source character set is UTF-8, we recommend that you use a compatible character set, such as UTF-8 or UTF-16, in the target database to avoid issues such as garbled characters due to incompatible character sets.

• If the clocks between nodes or between the client and the server are out of synchronization, the latency (for incremental synchronization or reverse increment) may be inaccurate.

  For example, if the clock is earlier than the standard time, the latency can be negative. If the clock is later than the standard time, the latency can be positive.

• During a data migration task between OceanBase databases, if the source OceanBase database is of a version earlier than V3.2.x and the source table has a global unique index and multiple partitions, and you update the partition key of the table, data may be lost during the data migration.

• Make sure that the migration precision of data types such as DECIMAL, FLOAT, or DOUBLE meets your expectations in OMS. If the precision of the target data type is smaller than that of the source data type, the target data may be truncated when it is migrated to the target column with a smaller precision. In this case, the data in the source column is inconsistent with that in the target column.

• If you change the unique index in the target database without enabling DDL synchronization, you must restart the incremental synchronization component. Otherwise, the data in the target database may be inconsistent with that in the source database.

• If the data migration task is not enabled for forward switchover, you must delete the unique indexes and pseudo columns in the target database. Otherwise, data cannot be written to the target database, and when data is imported to the downstream system, the pseudo columns are re-created, which causes conflicts with the pseudo columns in the source database.

  If the data migration task is enabled for forward switchover, OMS automatically deletes hidden columns and unique indexes based on the type of the data migration task. For more information, see Data migration service hidden column mechanism.

• In multi-table aggregation scenarios:

  • We recommend that you map the relationships between the source and target databases by using matching rules.

  • We recommend that you manually create schemas in the target database. If you use OMS to create schemas, skip failed objects in the schema migration step.

• If the source database is an OceanBase database and DDL synchronization is enabled, we recommend that you restart the data migration task if a table in the source database is renamed. This ensures that the data is not lost during incremental synchronization.

• If the table objects in the source and target databases differ only in capitalization, the data migration result may not be as expected because the object names in the source and target databases are case-insensitive.

• These points apply only to the MySQL compatible mode of OceanBase Database:

  • By default, when you migrate data between MySQL-compatible tenants of OceanBase Database, the parameter lower_case_table_names is set to 1 in the target database, and database objects in the target database are created in lowercase.

  • If the schemas of the source and target tables are inconsistent, the data in the two databases may be inconsistent. Known scenarios are as follows:

    • When you manually create a table schema in the target database, if the data types of columns in the source and target columns are not supported by OMS, implicit data type conversion may occur, which causes inconsistent column types between the source and target columns.

    • If the length of a column in the target database is shorter than that in the source database, the data in this column may be truncated, which causes inconsistent data between the source and target databases.

• These points apply only to the Oracle compatible mode of OceanBase Database:

  • A primary key table is a table that contains the pk and not null uk columns but does not contain the function-based uk column.

    ​If the source database is earlier than V2.2.77 or the source table contains a function-based uk on a virtual column, OMS may fail to accurately identify whether the source table is a primary key table. In this case, the full migration and full verification may be performed at a slower speed, and the incremental synchronization may be performed at an inconsistent speed.

  • The ALL_TABLES view in OceanBase Database of the Oracle compatible mode of V2.2.76 and earlier may incorrectly identify a partitioned table as a non-partitioned table and cause OMS to read incorrect view data. In this case, manually create the table in the target database. For more information, see Create a partitioned table.

  • If you skip the "Source-Primary Database-ROW MOVEMENT Check" precheck item and synchronize a table where ROW MOVEMENT is enabled, the data in the source and target databases may be inconsistent.

• If you configure only Incremental Synchronization when you create a data migration task, OMS requires that the archive logs in the source database be retained for more than 48 hours.

  ​If you configure Full Migration + Incremental Synchronization when you create a data migration task, OMS requires that the archive logs in the source database be retained for at least seven days. Otherwise, the data migration task may fail or the data in the source and target databases may be inconsistent because OMS cannot obtain incremental logs.

• If you perform incremental synchronization with OceanBase Database as the source or reverse incremental synchronization with OceanBase Database as the target and the database table objects contain UDT columns, the incremental synchronization task may fail due to unsupported UDT columns.

Supported sources and targets

The following table describes the sources and the targets supported for data migration between OceanBase Database in MySQL compatible mode and OceanBase Database in Oracle compatible mode. In the table, OceanBase Database in MySQL compatible mode is abbreviated as OB_MySQL, and OceanBase Database in Oracle compatible mode is abbreviated as OB_Oracle.

Procedure

1. Create a data migration task.

   

   1. Log in to the OMS console.

   2. In the left-side navigation pane, click Data Migration.

   3. On the Data Migration page, click Create Task in the upper-right corner.

2. On the Create Task page, specify the task name.

   We recommend that you use a combination of Chinese characters, numbers, and letters. The name cannot contain spaces and must be 64 characters or less in length.

   Notice

   The task name is a unique identifier in the OMS system. We recommend that you use a custom name.

3. On the Select Source and Target page, configure the parameters.

   

   Parameter	Description
   Source	If you have created an OceanBase data source (including a physical data source, public cloud data source, or standalone data source), select it from the drop-down list. Otherwise, click Create Data Source in the drop-down list to create one. For more information, see Create a physical data source for OceanBase Database, Create a public cloud data source for OceanBase Database, or Create a standalone data source for OceanBase Database.
   Target	If you have created an OceanBase data source (including a physical data source, public cloud data source, or standalone data source), select it from the drop-down list. Otherwise, click New Data Source in the drop-down list to create one.
   Tags (Optional)	Click the field and select a tag from the drop-down list. You can also click Manage Tags in the upper-right corner to create, modify, or delete a tag. For more information, see Manage tags of a data migration task.

4. Click Next. On the Select Migration Type page, select One-way Synchronization for Synchronization Topology.

   OMS supports One-way Synchronization and Bidirectional Synchronization. This topic describes how to configure a one-way synchronization task. For more information about how to configure a bidirectional synchronization task, see Configure a bidirectional synchronization task.

5. In the Migration Options section, select the migration type for the current data migration task.

   

   Options for Migration Type are Schema Migration, Full Migration, Incremental Synchronization, and Reverse Increment.

   Migration type	Description
   Schema Migration	After the schema migration task starts, OMS migrates data objects in the source database to the target database and automatically filters out temporary tables.
   Full Migration	After the full migration task starts, OMS migrates the existing data in the source table to the corresponding table in the target database. If you select Full Migration, we recommend that you collect the statistics of the source OceanBase database before the migration. For more information, see Manually collect statistics.
   Incremental Synchronization	After the incremental synchronization task starts, OMS synchronizes the data that is added, modified, or deleted in the source database to the corresponding table in the target database. Incremental Synchronization includes DML synchronization and DDL synchronization, and you can configure them as needed. For more information, see Configure DDL/DML.Incremental Synchronization has the following limitations: If you select DDL synchronization, OMS may interrupt the data migration when the source database performs a DDL operation that is not supported by OMS. If the DDL operation is to add a column, OMS may interrupt the data migration if you set the column attribute to NOT NULL.
   Reverse Increment	After the reverse increment task starts, OMS can synchronize the changes in the target database after the business switch to the source database in real time. Usually, the reverse increment task reuses the configurations of incremental synchronization. You can also configure them as needed. If the table to be migrated does not have a primary key, unique index, or has a large change volume, OMS may take a long time to synchronize data in the reverse increment task. In this case, you can add a unique index to the source database. You cannot select Reverse Increment in the following cases: Multi-table aggregation is involved. Multiple source schemas map to the same target schema.

6. (Optional) Click Next.

   If you select Schema Migration, Incremental Synchronization, or Reverse Increment, but the corresponding parameters are not configured for the OceanBase data source at the source or target, a dialog box titled Add Data Source Information appears, reminding you to configure the parameters. For more information, see Create a physical data source for OceanBase Database, Create a public cloud data source for OceanBase Database, or Create a standalone data source for OceanBase Database.

   After the parameters are configured, click Test connectivity. If the connection is established, click Save.

7. Click Next. On the Select Migration Objects page, select the objects to migrate.

   You can use the Specify Objects and Match by Rule options to select migration objects. This topic describes how to select migration objects using the Specify Objects option. For information about how to configure matching rules, see Configure matching rules.

   Notice

   • If the name of a database or table contains the characters "$$", the data migration task cannot be created.

   • If you selected DDL Synchronization in the Choose Migration Type step, we recommend that you select the matching rules to specify migration objects. This way, you can ensure that all new objects that meet the migration object rules are synchronized. If you specify migration objects by using the Specify Object option, new objects or renamed objects will not be synchronized.

   • OMS automatically filters out unsupported objects. For information about the SQL statements for querying objects, see SQL statements for querying database objects.

   

   1. On the Select Migration Objects page, set the Specify Object parameter to Specify Objects.

   2. Select the tables and views in the Source Object(s) list that you want to migrate. You can select tables and views in one or more databases.

   3. Click > to add them to the Target Object(s) list.

   OMS allows you to import objects by using a text file, rename objects, configure row filters, select partitions and columns, and remove one or all migration objects.

   Note

   When you use the Matching Rules method to select migration objects, the rename capability is replaced by the matching rules syntax. You can only set filter conditions. For more information, see Configure matching rules.

   Operation	Steps
   Import objects	In the Target Object(s) list, click the Import Objects icon in the upper-right corner. In the dialog box that appears, click OK. Notice: Importing overwrites the results of previous operations. Proceed with caution. In the Import Migration Objects dialog box, select the objects to be migrated. You can import a CSV file to rename databases and tables and configure row filters. For more information, see Download and import migration object configurations. Click Validate. If the imported objects are valid, click OK.
   Rename objects	OMS allows you to rename migration objects. For more information, see Rename a database or table.
   Configure settings	OMS allows you to configure row filters, select partitions, and specify columns to be migrated. Hover the pointer over the target object in the right-side list of the selection area. Click Settings that appears. In the Settings dialog box, you can perform the following operations: In the Row Filters section, configure row filters by entering WHERE clauses of standard SQL statements. For more information, see Filter data by using SQL conditions. In the Partition section, select the specified partition data that you want to obtain in full migration. After you select a partition, click OK. In the Select Columns section, select the columns to be migrated. For more information, see Column filtering.
   Remove one or all objects	OMS allows you to remove one or all selected objects from the target list. Remove a migration object Hover the pointer over the target object in the Target Object(s) list and click the Remove icon displayed. Remove all migration objects Click the Remove All icon in the upper-right corner of the Target Object(s) list. In the dialog box that appears, click OK to remove all migration objects.

8. Click Next. On the Migration Options page, configure the parameters.

   • Schema Migration

     The parameters described below will be displayed only if you select One-way Synchronization > Schema Migration in the Select Migration Type step.

     

     Parameter	Description
     Automatically Enter Next Stage upon Completion	If you select schema migration and any other migration type, you can specify whether to automatically proceed to the next stage after schema migration is completed. The default value is Yes. You can also view and modify this value on the Schema Migration tab of the data migration task details page.
     Normal Index Migration Method	The migration method for non-unique key indexes associated with the migrated table objects. Valid values: Do Not Migrate, Migrate with Schema, and Post-Full-Migration. The value Post-Full-Migration is displayed only if full migration is selected.

   • Full Migration

     The parameters described below will be displayed only if you select One-way Synchronization > Full Migration in the Select Migration Type step.

     

     Parameter	Description
     Full Migration Rate Limit	You can choose whether to limit the full migration rate as needed. If you choose to limit it, you must specify the RPS and BPS. The RPS specifies the maximum rows of data migrated to the target database per second during full migration, and the BPS specifies the maximum amount of data in bytes migrated to the target database per second during full migration. Note The RPS and BPS specified here only serve as throttling capabilities. The actual full migration performance is limited by factors such as the source and target databases and the instance specifications.
     Full Migration Resource Configuration	You can select the default settings of read concurrency, write concurrency, and memory for full migration, or customize the resource configuration for full migration. The resource configuration for full migration component Full-Import limits the resource consumption of the full migration phase of the task. Note The minimum value is 1 and only integers are supported.
     Handle Non-empty Tables in Target Database	Valid values: Ignore and Stop Migration. If you select Ignore, when the data to be inserted conflicts with the existing data of a target table, OMS retains the existing data and records the conflict data. Notice If you select Ignore, data is pulled in IN mode for full verification. In this case, the scenario where the target table contains more data than the source table cannot be verified, and the verification efficiency will be decreased. If you select Stop Migration and a target table contains data, an error is returned during full migration, indicating that the migration is not allowed. In this case, you must clear the data in the target table before you can continue with the migration. Notice After an error is returned, if you click Resume in the dialog box, OMS ignores this error and continues to migrate data. Proceed with caution.

   • Incremental Synchronization

     The parameters described below will be displayed only if you select One-way Synchronization > Incremental Synchronization in the Select Migration Type step.

     

     Parameter	Description
     Incremental Synchronization Rate Limit	You can choose whether to limit the incremental synchronization rate as needed. If you choose to limit it, you must specify the RPS and BPS. The RPS specifies the maximum rows of data synchronized to the target database per second during incremental synchronization, and the BPS specifies the maximum amount of data in bytes synchronized to the target database per second during incremental synchronization. Note The RPS and BPS specified here only serve as throttling capabilities. The actual incremental synchronization performance is limited by factors such as the source and target databases and the instance specifications.
     Incremental Log Pull Resource Configuration	You can select Small, Medium, or Large to use the corresponding default value of Memory. You can also customize the resource configurations for incremental log pull. By setting the resource configuration for the Store component, you can limit the resource consumption of a task in log pull in the incremental synchronization stage. Note The minimum value is 1 and only integers are supported.
     Incremental Data Write Resource Configuration	You can select the default settings of write concurrency and memory for incremental data write, or customize the resource configuration for incremental data write. The resource configuration for incremental synchronization component Incr-Sync limits the resource consumption of data write in the incremental synchronization phase of the task. Note The minimum value is 1 and only integers are supported.
     Incremental Record Retention Duration	The duration that incremental parsed files are cached in OMS. A longer retention duration results in more disk space occupied by the Store component.
     Incremental Synchronization Start Timestamp	If you have selected Full Migration as the migration type, this parameter is not displayed. If you have selected Incremental Synchronization but not Full Migration, specify a point in time after which the data is to be synchronized. The default value is the current system time. For more information, see Set an incremental synchronization timestamp.

   • Reverse Increment

     The parameters described below will be displayed only if you select One-way Synchronization > Reverse Increment in the Select Migration Type step. The parameters for reverse increment are the same as those for incremental synchronization. You can select the Reuse Incremental Synchronization Configuration check box in the upper-right corner.

     

   • Advanced Options

     Parameter	Description
     Add Hidden Columns for Tables Without Non-null Unique Keys	If data is to be migrated between OceanBase databases, you need to specify whether to add hidden columns for tables without non-null unique keys. For more information, see Hidden column mechanisms. If you set the value to No, if the table to be migrated does not have a primary key or a non-null unique key, data duplication may occur when the task is restarted or encounters other exceptions. We recommend that you configure a non-null unique key for all tables.
     Target Table Storage Type	This parameter is displayed only if the target is OceanBase database V4.3.0 or later and you selected DDL synchronization or Incremental Synchronization > DDL synchronization in the Select Migration Type step. The valid values are Default, Row Storage, Column Storage, and Hybrid Row-Column Storage. This parameter specifies the storage type for target table objects during schema migration or incremental synchronization. For more information, see default_table_store_format. Note The value Default means that other parameters are automatically set based on the parameter configurations of the target database. Table objects in schema migration and new table objects created by incremental DDL statements are written to corresponding schemas based on the specified storage type.
     Source Table Object Storage Type	This parameter is displayed only if the source OceanBase database is V4.3.0 or later, and you selected Reverse Increment > DDL synchronization in the Select Migration Type step. The valid values are Default, Row Storage, Column Storage, and Hybrid Row-Column Storage. This parameter determines the storage type for table objects in the source database for incremental DDL synchronization in reverse increment. For more information, see default_table_store_format. Note The value Default means that other parameters are automatically set based on the parameter configurations of the target database. New table objects created by incremental DDL statements in reverse increment are written to corresponding schemas based on the specified storage type.

   If the parameters on the current page cannot satisfy your requirements, you can click Parameter Configuration at the bottom of the page to configure the parameters in more details. If you have a preconfigured task template or component template, you can also reference them here.

   

9. Click Precheck. The system performs a precheck on the data migration task.

   In the Precheck step, OMS checks whether the database user has the required read/write permissions and whether the database network connection is established. The data migration task cannot be started unless all checks are passed. If the precheck fails:

   • You can troubleshoot the issues and retry the precheck until it succeeds.

   • You can also click Skip in the Actions column of the failed check item. A dialog box then appears, describing the impact of the skipped operation. After you confirm the skip, click OK in the dialog box.

10. Click Start Task. If you do not want to start the task immediately, you can click Save to go to the details page of the data migration task, where you can start the task at any time.

You can click Configure Validation Task in the upper-right corner of the data migration details page to compare the data between the source and target databases. For more information, see Create a data validation task.

During the data migration task, you can modify the migration objects. For more information, see View and modify migration objects. After the data migration task starts, it will proceed to the next phase based on the selected migration type. For more information, see the View Migration Details section in View details of a data migration task.