Migrate data from a MySQL database to a MySQL tenant of OceanBase Database

This topic describes how to use OceanBase Migration Service (OMS) to migrate data from a MySQL database to a MySQL tenant of OceanBase Database.

Background

You can create a data migration project in the OMS console to migrate the existing business data and incremental data from a MySQL database to a MySQL tenant of OceanBase Database through schema migration, full migration, and incremental synchronization.

The MySQL database supports the following modes: primary database only, standby database only, and primary/standby databases. The following table describes the data migration operations supported by each mode.

Prerequisites

• You have created a corresponding schema in the destination MySQL tenant of OceanBase Database. OMS allows you to migrate tables and columns. Therefore, you must create a corresponding schema in the destination database before migration.

• You have enabled binlogs for the self-managed MySQL database. For more information, see Enable binlogs for the MySQL database.

• You have created dedicated database users in the source MySQL database and the destination MySQL tenant of OceanBase Database for data migration and granted the corresponding privileges to the users. For more information, see Create a database user.

  Database	Schema migration	Full migration	Incremental synchronization
  Self-managed MySQL database	SELECT privilege For MySQL 8.0, the SHOW VIEW privilege is also required.	SELECT privilege	REPLICATION SLAVE, REPLICATION CLIENT, SHOW VIEW, and SELECT privileges
  MySQL tenant of OceanBase Database	CREATE, CREATE VIEW, SELECT, INSERT, UPDATE, and DELETE privileges	Read/Write privileges	Read/Write privileges

Limits

• OMS supports the following MySQL database versions: 5.5, 5.6, 5.7, and 8.0. OMS supports only the MySQL InnoDB storage engine, and is unavailable for other engines.

• MySQL tenants of OceanBase Database V4.0.0 can be used only as the destination of migration.

• The pre-check fails if the primary key is data of the FLOAT or DOUBLE type. We recommend that you do not use data of these types as the primary key.

• OMS does not support triggers in the destination database for long-term synchronization between these databases.

• OMS does not support an index field greater than 767 bytes (or 191 characters) in length for MySQL.

• The data source identifiers and user accounts must be globally unique in OMS.

• OMS allows you to migrate only databases and tables whose names are ASCII codes and do not contain special characters such as .|"'`()=;/&\n.

• A MySQL tenant of OceanBase Database V3.2.0 supports either the change or modify column operation in one statement.

• If the lower_case_table_names settings of the source and destination are different, the project cannot be created. In addition, OMS does not support the case sensitivity of MySQL databases and OceanBase databases. That is, even when lower_case_table_names=0 is set in the source and destination databases, projects cannot be created.

  By default, OMS uses the lower_case_table_names = 1 setting in the destination and creates objects named in lower case in the destination.

• OMS does not support CASCADE foreign key migration for source MySQL databases.

• The clock of the source database is synchronized with that of the destination database.

• OMS supports full synchronization of tables whose partition fields are not within the primary keys, but does not support DDL operations that create tables.

Considerations

• The host of the MySQL database must have sufficient outbound bandwidth. Insufficient outbound bandwidth on the host will slow down log parsing and data migration and may increase the latency of data synchronization.

• If the clocks are out of synchronization between the nodes or between the client and the server, a negative delay may occur in incremental synchronization or reverse incremental synchronization.

• During reverse incremental migration from a MySQL database to a MySQL tenant of OceanBase Database, if the MySQL tenant 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.

• If collations of the source and destination databases are different, a table whose primary key is data of the VARCHAR type fails the data verification.

• If incremental parsing is required for the MySQL database, you must specify the ID of the MySQL server.

• If you change the unique index of the destination, you must restart the incremental synchronization. Otherwise, the data may be inconsistent.

• When the length of a field in the destination database is shorter than that in the source database, the data of this field is automatically truncated by the database, which causes data inconsistency between the source and destination databases.

• If you select migration objects based on matching rules, we recommend that you create standard CTAS statements and set object exclusion rules, such as a.ctas*, to avoid interrupting the data migration project.

• In a multi-table aggregation scenario:

  • We recommend that you map objects in the source and destination databases by importing objects and configuring matching rules.

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

• If you skip the "Check the ROW_MOVEMENT parameter of the database" check item of the source primary database during the migration, data inconsistency may occur when you synchronize tables whose ROW_MOVEMENT is enable.

Data type mappings

Procedure

1. Create a migration project.

   1. Log on to the OMS console.

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

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

2. On the Select Source and Destination page, specify the following 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. Notice The project name must be a unique identifier in the OMS system.
   Tag	Click the field and select a target tag from the drop-down list. You can 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 MySQL data source, select it from the drop-down list. If you have not created a MySQL data source, click Create 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 MySQL data source. Note: If you select Allow OMS to automatically write heartbeat data into this instance during incremental synchronization. This resolves the problem of high latency when no business data is written in the source database when you add a MySQL data source, OMS will create and update the drc.heartbeat table in the corresponding MySQL database. In that case, the MySQL database user must have the privileges to create and write the table. For more information, see Create and update a heartbeat table. You can select a MySQL data source in primary database only mode or primary/standby databases mode. This topic describes how to create a data migration project with a MySQL data source in primary/standby databases mode.
   Destination	If you have created a data source for the MySQL tenant of OceanBase Database, select it from the drop-down list. If you have not created a data source for the MySQL tenant, click Create Data Source in the drop-down list and create one in the dialog box that appears on the right. For more information, see Create a physical data source of OceanBase Database.
   Scenario	Valid values: Tables with Unique Key and All Tables. If a table has primary key constraints or unique constraints, and fields in the table are unique, this table is a table with a unique key. If you select All Tables, tables that have unique and non-unique keys, except for temporary tables, are included.

3. Click Next.

   If you have selected Tables with Unique Key for Scenario, click OK in the dialog box that appears.

4. On the Select Migration Type page, specify related parameters.

   Options available for Migration Type include Schema Migration, Full Migration, Incremental Synchronization, Full Verification, and Reverse Incremental Migration.

   Migration type	Limits
   Schema Migration	In a project that migrates schemas from a MySQL database to a MySQL tenant of OceanBase Database, the database that does not exist in the destination can be automatically created.
   Full Migration	If you select Full Migration, we recommend that you use the ANALYZE statement to collect the statistics of the MySQL database before data migration.
   Incremental Synchronization	Options for Incremental Synchronization are DML Synchronization and DDL Synchronization. You can select the options as needed. For more information about DDL synchronization, see Synchronize DDL operations from a MySQL database to a MySQL tenant of OceanBase Database. Incremental Synchronization has the following limits: If you select Incremental Synchronization, you need to enable binlogs for the source MySQL database, and set binlog_row_image to full and binlog_format to row. If you select Incremental Synchronization, the binlogs of the MySQL database must be retained for no less than 24 hours. Otherwise, the migration project may be interrupted because of the absence of binlogs, which cannot be recovered. If you select DDL Synchronization, when you perform a DDL operation that is not supported by OMS in the source database, 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	If you select Full Verification, we recommend that you collect the statistics of the MySQL database and the MySQL tenant of OceanBase Database before full verification. For more information about how to collect statistics of a MySQL tenant of OceanBase Database, see Manually collect statistics. If you have selected Incremental Synchronization but did not select all DML statements in the DML Synchronization section, OMS does not support full verification. OMS supports full data verification of only tables with a unique key.
   Reverse Incremental Migration	You cannot select Reverse Incremental Migration in the following cases: Multi-table aggregation and synchronization is enabled. Multiple schemas are configured in a rule to match one type of objects.

5. (Optional) Click Next. If you have selected Reverse Incremental Migration but the ConfigUrl, username, or password is not configured for the data source of the destination MySQL tenant of OceanBase Database, the More about Data Sources dialog box appears, prompting you to configure related parameters. For more information, see Create a physical data source of OceanBase Database.

   After you configure the parameters, click Test Connectivity. After the test succeeds, click Save.

6. Click Next. On the Select Migration Objects page, select the migration objects and migration scope.

   You can select one of the following two modes to migrate objects: Specify Objects or Match Rules. If you have selected DDL Synchronization, only the Match Rules option is available.

   • 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.

     • Do not select a table named in the format of *_ghc.

     • If the database or table name contains a double dollar sign ($$), you cannot create the migration project.

     When you migrate data from a MySQL database to a MySQL tenant of OceanBase Database, OMS allows you to import objects through text, rename object names, set row filters, view column information, and remove one or all objects to be migrated.

     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 allows you to rename the migration objects. For more information, see Rename a database table.
     Settings	OMS allows you to use the WHERE clause to filter rows. 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	During data mapping, OMS allows you to remove one or more selected objects to be migrated to the destination. 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.

     Notice

     Set Object Exclusion Rule to {database_name}.*_ghc.

7. Click Next.

   If you select All Tables for Scenario, click Next in the dialog box that appears.

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

   Parameter	Description
   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. You can select a point in time or enter a timestamp. Notice You can select the current time or a point in time earlier than the current time. This parameter is closely related to the retention period of archived logs. Generally, you can start data synchronization from the current timestamp.
   Concurrency for Full Migration	The value can be Smooth, Normal, or Fast. The quantity of resources to be consumed by a full data migration task varies based on the migration performance. You can also modify the configurations of the Full-Import component to customize the concurrency. Notice: To enable this feature, select Full Migration on the Select Migration Type page.
   Full Verification Concurrency	The value can be Smooth, Normal, or Fast. Different quantities of resources of the source and destination databases are consumed at different concurrencies. You can also modify the configurations of the Full-Verification component to customize the concurrency.
   Incremental Record Retention Time	The duration that incremental parsed files are cached in OMS. A longer retention period indicates more disk space occupied by the Store component of OMS.
   Whether to Allow Destination Table to Be Not Empty During Full Migration	If destination tables are allowed to be not empty during full migration, full verification is performed in IN mode. Notice: To enable this feature, select Full Migration on the Select Migration Type page.
   Whether to Allow Post-indexing	You can specify whether to allow post-indexing after full migration is completed. Post-indexing can shorten the time of full migration. Notice: To enable this feature, select both Schema Migration and Full Migration on the Select Migration Type page. Only non-unique key indexes can be created after the migration is completed.

9. Click Precheck to start a pre-check on the data migration project.

   During the pre-check, OMS checks the read and write privileges of the database users and the network connections of the databases. The data migration project can be started only after it passes all check items. If an error is returned during the pre-check:

   • You can identify and troubleshoot the problem and then perform the pre-check again.

   • You can click Skip in the Actions column of the pre-check item with the error. A dialog box will be displayed, prompting the impact caused if you skip this error. If you want to continue, click OK in the dialog box.

10. 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 allows you to modify the migration objects when the data migration project is running. For more information, see View and modify migration objects. After a data migration project is started, the migration objects will be executed based on the selected migration type. For more information, see the "View migration details" section in the View details of a data migration project topic.