This topic describes how to use OceanBase Migration Service (OMS) Community Edition to migrate data within OceanBase Database Community Edition.
Background information
You can create a data migration project in the console of OMS Community Edition to seamlessly migrate the existing business data and incremental data within OceanBase Database Community Edition through schema migration, full migration, and incremental synchronization.
Prerequisites
You have created a corresponding schema in the destination database. OMS Community Edition allows you to migrate tables and columns. Therefore, you must create a corresponding schema in the destination database before migration.
You have created dedicated database users for data migration in the source and destination databases, and granted corresponding privileges to the users. For more information, see Create a database user.
If you want to migrate data from a table without a primary key, create a user and grant privileges to the user as needed before the migration. For more information, see Create the __oceanbase_inner_drc_user user.
Limitations
Limitations on the source database
Do not perform DDL operations for database or schema changes during schema migration or full data migration. Otherwise, the data migration project may be interrupted.
When
useTargetSchemais set tofalsein incremental synchronization, if the destination uses a field of the BINARY type as the primary key or unique key, and the length of the data at the source is different from the length of the field of the BINARY type at the destination, no data is matched for the UPDATE or DELETE operation. This causes data quality risks.The data source identifiers and user accounts must be globally unique in OMS Community Edition.
If temporary tables exist in OceanBase Database Community Edition of a version earlier than V4.0.0, full migration fails.
OMS Community Edition supports the migration of only objects whose database name, table name, and column name are ASCII-encoded without special characters. The special characters are line breaks and . | " ' ` ( ) = ; / &
OMS Community Edition allows you to migrate both tables with primary keys and tables without primary keys within OceanBase Database Community Edition.
If the destination is a database, OMS Community Edition does not support triggers in the destination database. If triggers exist in the destination database, the data migration may fail.
The source cannot be a standby OceanBase database.
Considerations
If you use OceanBase Database Community Edition V4.x, we recommend that you enable log archiving. If you enable log archiving, OMS Community Edition implements incremental synchronization by consuming archive logs after clogs are recycled. For more information about how to enable log archiving, see the Log archive chapter.
If the UTF-8 character set is used in the source, we recommend that you use a compatible character set, such as UTF-8 or UTF-16, in the destination to avoid garbled characters.
If the clocks between nodes or between the client and the server are out of synchronization, the latency may be inaccurate during incremental synchronization or reverse incremental migration.
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.
When you migrate data within OceanBase Database Community Edition, if the source database is of a version earlier than V3.2.x and contains a multi-partition table that has a globally unique index, data may be lost during migration if you update the value of the partitioning key of the table.
Check whether the migration precision of OMS Community Edition for columns of data types such as DECIMAL, FLOAT, and DOUBLE is as expected. If the precision of the destination field type is lower than the precision of the source field type, the value with a higher precision may be truncated. This may result in data inconsistency between the source and destination fields.
When DDL synchronization is disabled, if you change the unique index of the destination, you must restart the Incr-Sync component. Otherwise, the data may be inconsistent.
If forward switchover is disabled for a data migration project, delete the unique indexes and pseudocolumns from the destination. If you do not delete the unique indexes and pseudocolumns, data cannot be written, and pseudocolumns will be generated again when data is imported to the downstream system, causing conflicts with the pseudocolumns in the source.
If forward switchover is enabled for the data migration project, OMS Community Edition automatically deletes hidden columns and unique indexes based on the type of the migration project. For more information, see Schema migration mechanisms.
If you configure matching rules to select tables created by using the CREATE TABLE AS SELECT (CTAS) statement as migration objects, we recommend that you configure the rules, such as
a.*_2023_backup, in advance to avoid interruption of the migration project.In a multi-table aggregation scenario:
We recommend that you map objects in the source and destination by importing objects and configuring matching rules.
We recommend that you manually create schemas at the destination. If you use OMS Community Edition to create schemas, skip failed objects in the schema migration step.
In a data migration project where the source is OceanBase Database Community Edition and DDL synchronization is enabled, if a RENAME operation is performed on a table in the source, we recommend that you restart the project to avoid data loss during incremental synchronization.
By default,
lower_case_table_namesis set to1at the destination, and the destination database objects are created with lowercase names.
Procedure
Create a data migration project.
Log on to the console of OMS Community Edition.
In the left-side navigation pane, click Data Migration.
On the Data Migration page, click Create Migration Project in the upper-right corner.
On the Select Source and Destination page, configure the parameters.
Parameter Description Migration Project Name We recommend that you set it to a combination of digits and letters. It must not contain any spaces and cannot exceed 64 characters in length. Tag Click the field and select a target tag from the drop-down list. You can also click Manage Tags to create, modify, and delete tags. For more information, see Use tags to manage data migration projects. Source If you have created a data source of OceanBase Database Community Edition, select it from the drop-down list. If not, click New Data Source in the drop-down list and create one in the dialog box that appears on the right. For more information about parameters, see Create a data source of OceanBase Database Community Edition. Destination If you have created a data source of OceanBase Database Community Edition, select it from the drop-down list. If not, click New Data Source in the drop-down list and create one in the dialog box that appears on the right. Scenarios Two scenarios are available: Data Migration and Active-Active Disaster Recovery. Select Data Migration. To create a migration project in an active-active disaster recovery scenario, you need to select Active-Active Disaster Recovery. For more information, see Active-active disaster recovery within OceanBase Database Community Edition. Click Next.
On the Select Migration Type page, configure the parameters.
Options for Migration Type are Schema Migration, Full Migration, Incremental Synchronization, Full Verification, and Reverse Incremental Migration.
Migration type Description Schema migration The definitions of data objects, such as tables, indexes, constraints, comments, and views, are migrated from the source database to the destination database. Temporary tables are automatically filtered out. Full migration The existing data is migrated from tables in the source database to the corresponding tables in the destination database. If you select Full Migration, we recommend that you collect the statistics of the source database before data migration. Incremental synchronization Changed data in the source database is synchronized to the corresponding tables in the destination database after an incremental synchronization task starts. Data changes are data addition, modification, and deletion.
Options for Incremental Synchronization are DML Synchronization and DDL Synchronization. You can select the options as needed. For more information about DDL synchronization, see Supported DDL operations in incremental migration between MySQL tenants of OceanBase Database. Incremental Synchronization has the following limitations:- If you select DDL Synchronization, when you perform a DDL operation in the source database that cannot be synchronized by OMS Community Edition, data migration may fail.
- If the DDL operation creates a new column, we recommend that you set the attribute of the column to Null. Otherwise, data migration may be interrupted.
Full verification After the full data migration and incremental data synchronization are completed, OMS Community Edition automatically initiates a full data verification task to verify the data tables in the source and destination databases. - If you select Full Verification, we recommend that you collect the statistics of both the source and destination databases before full verification. For more information, see Manually collect statistics.
- If you select Incremental Synchronization but do not select all DML operations in the DML Synchronization section, you cannot select Full Verification.
Reverse incremental migration Data changes made in the destination database after the business database switchover are applied to the source database in real time. If a table to migrate has no primary key or unique index and a large amount of data in the table is changed, the reverse incremental migration will take a long time. In this case, you can add unique indexes in the source database.
You cannot select Reverse Incremental Migration in the following cases:- The Active-Active Disaster Recovery scenario is selected.
- Multi-table aggregation and synchronization is enabled.
- Multiple source schemas map to the same destination schema.
(Optional) Click Next.
Specify the related information for the source database.
For incremental synchronization, specify the ConfigUrl, username, and password.
For schema migration, specify the username and password.
For the migration of a table without a unique key, specify the password of
_OCEANBASE_INNER_DRC_USER.
For reverse incremental migration, specify the ConfigUrl, username, and password of the source database.
If you have selected Schema Migration, Incremental Synchronization, or Reverse Incremental Migration but no related parameters are configured for the data source of the source or destination database, the More about Data Sources dialog box appears, prompting you to configure related parameters. For more information about parameters, see Create a data source of OceanBase Database Community Edition.
After you configure the parameters, click Test Connectivity. After the test succeeds, click Save.
Click Next. On the Select Migration Objects page, select the migration objects and migration scope.
You can select Specify Objects or Match Rules to specify the migration objects.
Select Specify Objects. Then select the objects to be migrated on the left and click > to add them to the list on the right. You can select tables and views of one or more databases as the migration objects.
Notice
The names of tables to be migrated, as well as the names of columns in the tables, must not contain Chinese characters.
If the database or table name contains a double dollar sign ($$), you cannot create the migration project.
After you select migration objects by using the Specify Objects option, the DDL operations take effect only for selected objects, and table creation is not supported.
OMS Community Edition also allows you to import objects from text, rename objects, set row filters, view column information, and remove a single migration object or all migration objects.
Operation Step Import Objects - In the list on the right of the Specify Migration Scope section, click Import Objects in the upper-right corner.
- In the dialog box that appears, click OK.
Notice
This operation will overwrite previous selections. Proceed with caution. - In the Import Objects dialog box, import the objects to be migrated.
You can import CSV files to rename databases/tables and set row filtering conditions. For more information, see Download and import the settings of migration objects. - Click Validate.
- After the validation succeeds, click OK.
Rename OMS Community Edition allows you to rename migration objects. For more information, see Rename a database table. Settings OMS Community Edition allows you to filter rows by using WHEREconditions. For more information, see Use SQL conditions to filter data.
You can also view column information of the migration object in the View Column section.Remove/Remove All OMS Community Edition allows you to remove a single object or all objects to be migrated to the destination database during data mapping. - To remove a single migration object:
In the list on the right of the Specify Migration Scope section, hover the pointer over the target object, and click Remove. - To remove all migration objects:
In the list on the right of the Specify Migration Scope section, click Remove All in the upper-right corner. In the dialog box that appears, click OK.
Select Match Rules. For more information, see Configure matching rules for migration objects.
Click Next. On the Migration Options page, specify the following parameters.
To view or modify parameters of the Full-Import or Incr-Sync component, click Configuration Details in the upper-right corner of the Full Migration or Incremental Synchronization section. For more information about the parameters, see Coordinator.
Schema migration
This section is displayed only when you have selected Schema Migration on the Select Migration Type page, the source database is OceanBase Database Community Edition of a version earlier than V4.0.0, and the destination database is OceanBase Database Community Edition V4.0.0 or later. You can specify the Character Set Mapping and Collation Mapping parameters as needed.
Full migration
The following table describes the full migration parameters, which are displayed only when you have selected Full Migration on the Select Migration Type page.
Parameter Description Concurrency Speed Valid values: Stable, Normal, Fast, and Custom. The amount of resources to be consumed by a full data migration task varies based on the migration performance. If you select Custom, you can set Read Concurrency, Write Concurrency, and JVM Memory as needed. Processing Strategy When Records Exist in Target Object Valid values: Ignore and Stop Migration. - If you select Ignore, the data in the source and destination databases may be inconsistent.
- If you select Stop Migration, the project is set to the Failed state when the system detects records in the destination table. To continue data migration, manually resume the project.
Whether to Allow Post-indexing Specifies whether to create indexes after the full migration is completed. Post-indexing can shorten the time required for full migration. For more information about the considerations on post-indexing, see the description below. Notice
This feature is supported only when you have selected both Schema Migration and Full Migration on the Select Migration Type page.
If post-indexing is allowed, we recommend that you adjust the parameters based on the hardware conditions of the destination database and the business traffic.
If you use OceanBase Database Community Edition V4.x, adjust the following parameters of the sys tenant and business tenants by using a command-line interface (CLI) client.
Adjust the parameters of the sys tenant
// parallel_servers_target specifies the queuing conditions for parallel queries on each server. // To maximize performance, we recommend that you set this parameter to a value greater than, for example, 1.5 times, the number of physical CPU cores. In addition, make sure that the value does not exceed 64, to prevent database kernels from contending for locks. set global parallel_servers_target = 64;Adjust the parameters of a business tenant
// Specify the limit on the file memory buffer size. alter system set _temporary_file_io_area_size = '10' tenant = 'xxx'; // Disable throttling in V4.x. alter system set sys_bkgd_net_percentage = 100;
If you use OceanBase Database Community Edition V3.x, adjust the following parameters of the sys tenant by using a CLI client.
// parallel_servers_target specifies the queuing conditions for parallel queries on each server. // To maximize performance, we recommend that you set this parameter to a value greater than, for example, 1.5 times, the number of physical CPU cores. In addition, make sure that the value does not exceed 64, to prevent database kernels from contending for locks. set global parallel_servers_target = 64; // data_copy_concurrency specifies the maximum number of concurrent data migration and replication tasks allowed in the system. alter system set data_copy_concurrency = 200;
Incremental synchronization
The following table describes the incremental synchronization parameters, which are displayed only when you have selected Incremental Synchronization on the Select Migration Type page.
Parameter Description Concurrency Speed Valid values: Stable, Normal, Fast, and Custom. The amount of resources to be consumed by an incremental synchronization task varies based on the synchronization performance. If you select Custom, you can set Read Concurrency, Write Concurrency, and JVM Memory as needed. Incremental Synchronization Start Timestamp - If you have set the migration type to Full Migration, 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.
Incremental Record Retention Time The duration that incremental parsed files are cached in OMS Community Edition. A longer retention period results in more disk space occupied by the Store component of OMS Community Edition.
Click Precheck to start a precheck on the data migration project.
During the precheck, OMS Community Edition checks the read and write privileges of the database users and the network connectivity of the databases. The data migration project can be started only after it passes all check items. If an error is returned during the precheck:
You can identify and troubleshoot the problem and then perform the precheck again.
You can also click Skip in the Actions column of the failed precheck item. A dialog box appears, prompting you the impact. If you want to skip this operation, click OK.
Click Start Project. If you do not need to start the project now, click Save to go to the details page of the data migration project. You can start the project later as needed.
OMS Community Edition allows you to modify the migration objects when the migration project is running. For more information, see View and modify migration objects. After a data migration project is started, the migration subtasks will be executed based on the selected migration types. For more information, see the "View migration details" section in the View details of a data migration project topic.