Migrate data from a MySQL database to OceanBase Database Community Edition

This topic describes how to use OceanBase Migration Service (OMS) Community Edition to migrate data from a MySQL database to 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 from a self-managed MySQL database to OceanBase Database Community Edition 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 enabled binlogs for the self-managed MySQL database. For more information, see Enable binlogs for the MySQL database.

• You have created dedicated database users for data migration in the self-managed MySQL database that serves as the source and OceanBase Database Community Edition that serves as the destination, and granted the corresponding privileges to the users. For more information, see Create a database user.

Limitations

• Limitations on the source database

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

• At present, MySQL 5.5, 5.6, 5.7, and 8.0 are supported. OMS Community Edition supports only the MySQL InnoDB storage engine and is unavailable for other engines.

• The precheck fails if the primary key is of the FLOAT or DOUBLE data type. We recommend that you do not specify a column of such a data type as the primary key.

• 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.

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

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

• 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 | " ' ` ( ) = ; / &

• If the lower_case_table_names settings of the source and destination are different, the project cannot be created. If lower_case_table_names is set to 0 in the source and destination databases, the source and destination databases are case-sensitive. In this case, the project cannot be created either.

  By default, lower_table_case_names is set to 1 in the destination, and the destination database objects are created with lowercase names.

• OMS Community Edition does not support the migration of cascading foreign keys from the source MySQL database.

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

Considerations

• To ensure the performance of a data migration project, we recommend that you migrate no more than 1,000 tables at a time.

• 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, which may increase the latency of data synchronization.

• If the source and destination databases use different collations, the data in the destination database may be inconsistent with that in the source database after data synchronization.

  • For example, if the collation for the source database is utf8mb4_0900_ai_ci and that for the destination database is utf8mb4_general_ci, two data records 'A' and 'A ' cannot be both written to the destination database, causing data loss.

  • Data inconsistency will be detected during verification for a table that uses a column of the VARCHAR type as the primary key.

• 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.

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

• 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.

• In reverse incremental migration from a MySQL database to OceanBase Database Community Edition of a version earlier than V3.2.x, if a source table is a multi-partition table with a global unique index and the values of the partitioning key of the table are updated, data can be lost during the migration.

• 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.

• Take note of the following considerations if you want to aggregate multiple tables:

  • We recommend that you configure the mappings between the source and destination databases by importing objects or specifying 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.

• OMS Community Edition supports data migration between tables that have different numbers of fields. If an error is reported because a field of the source table does not exist in the destination table during full migration or incremental synchronization, you can set the ignoreRedunantColumnsReplicate parameter of the Full-Import or Incr-Sync component to true and then resume the data migration project.

• A difference between the source and destination table schemas may result in data consistency. Some known scenarios are described as follows:

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

  • If the length of a column at the destination is shorter than that at the source, the data of this column may be automatically truncated, which causes data inconsistency between the source and destination.

Data type mappings

Procedure

1. Create a data migration project.

   1. Log on to the console of OMS Community Edition.

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

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

2. 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 MySQL data source, 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 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 Community Edition 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 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.
   Scenarios	Two scenarios are available: Data Migration and Active-Active Disaster Recovery. Select Data Migration. For more information about active-active disaster recovery scenarios, see Migrate data in active-active disaster recovery scenarios.
   Scenario type	Valid values: Tables with Unique Key and All Tables. A table with a unique key is one that has a primary key or a non-null unique key. If you select All Tables, tables that have primary key constraints, and unique and non-unique keys, except for temporary tables, are included. If you select Active-Active Disaster Recovery for Scenarios, you can migrate only tables with unique keys.

3. Click Next.

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

4. On the Select Migration Type page, configure the parameters.

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

   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. In a project that migrates schemas from a MySQL database to OceanBase Database Community Edition, the database that does not exist in the destination can be automatically created.
   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 Data Migration, we recommend that you use the ANALYZE statement to collect the statistics of the MySQL 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 from a MySQL database to OceanBase Database Community Edition and limitations. Incremental Synchronization has the following limitations: 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 at least 24 hours. Otherwise, the migration project may be interrupted and cannot be resumed because of the absence of binlogs. 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 about how to collect statistics of OceanBase Database Community Edition, 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. OMS Community Edition supports full data verification of only tables with a unique key.
   Reverse incremental migration	Data changes made in the destination database after the business database switchover are applied to the source database in real time. You cannot select Reverse Incremental Migration in the following cases: The Active-Active Disaster Recovery scenario is selected. When you create an active-active disaster recovery project to migrate data from a MySQL database to a MySQL tenant of OceanBase Database, you do not need to specify reverse incremental migration. OMS Community Edition automatically starts the reverse incremental migration after the project starts based on the settings of incremental synchronization. Multi-table aggregation and synchronization is enabled. Multiple source schemas map to the same destination schema.

5. (Optional) Click Next. If you have selected Reverse Incremental Migration but the ConfigUrl or RootService, username, or password is not configured for OceanBase Database Community Edition that serves as the destination, 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.

6. Click Next. On the Select Migration Objects page, specify the migration objects for the migration project.

   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.

     • 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.

     • 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	Description
     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 an object	OMS Community Edition allows you to rename migration objects. For more information, see Rename a database table.
     Configure settings	OMS Community Edition allows you to filter rows by using WHERE conditions. 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 one or all objects	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, move 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.

   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 if you have selected Schema Migration on the Select Migration Type page. 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 if 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, when the data to be inserted conflicts with the existing data of a destination table, OMS Community Edition retains the existing data and records the conflict data. Notice If you select Ignore, data is pulled in IN mode for verification. In this case, the scenario where the destination 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 destination table contains records, an error is returned during full migration, indicating that the migration is not allowed. In this case, you must clear the data in the destination table before you can continue with the migration. Notice After an error is returned, if you click Resume in the dialog box, OMS Community Edition ignores this error and continues to migrate data. Proceed with caution.
     Writing Method	Valid values: SQL (specifies to write data to tables by using INSERT or REPLACE) and Direct Load (specifies to write data through bypass import). The limitations on the Direct Load are as follows: This write mode is supported for full migration only when the destination is an instance of OceanBase Database Community Edition of a version later than V4.2.1. The size of data in a single row cannot exceed 2 MB. Only data duplication caused by primary key constraints can be handled, and that caused by unique key constraints cannot be handled. Generated columns, triggers, and user-defined types (UDTs) are not supported. Bypass import applies to empty tables and cannot be interrupted. In other words, resumable transmission is not supported. Therefore, if bypass import is used for full migration and is interrupted, the data in the source is read again even after the project resumes normal. If an imported table contains large object (LOB) fields, execute the following statement to disable the enable_rebalance parameter for OceanBase Database Community Edition: SHOW PARAMETERS LIKE 'enable_rebalance'; ALTER SYSTEM SET enable_rebalance = false; Requests in a queue may time out if data is concurrently written in bypass mode. We recommend that you set soure.sliceWorkerNum to 1. The number and order of fields in the source table must be the same as those in the destination table. In a multi-table aggregation scenario, data writing through bypass import is not supported.
     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 if 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.

       • Modify 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; 
         

       • Modify the parameters of a user 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 if 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 Data Migration, this parameter is not displayed. If you have selected Incremental Synchronization but not Full Data 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.

9. 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 perform the following operations:

   • Identify and troubleshoot the error and then perform the precheck again.

   • Click Skip in the Actions column of the failed precheck item. In the dialog box that prompts the consequences of the operation, click OK.

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 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.