Migrate data from a DB2 LUW database to an Oracle-compatible tenant of OceanBase Database

This topic describes how to use OceanBase Migration Service (OMS) to migrate data from a DB2 LUW database to an Oracle-compatible tenant of OceanBase Database, which can be a physical data source, a public cloud OceanBase data source, or a standalone data source.

Prerequisites

• You have created a corresponding schema in the target Oracle-compatible tenant of OceanBase Database.

  You must create a corresponding schema in the target database before migration. OMS will migrate the tables and views to the schema.

• You have created dedicated database users in the source DB2 LUW database and the target Oracle-compatible tenant of OceanBase Database for data migration and granted the required privileges to the users. For more information, see Create a database user.

• You have enabled ARCHIVELOG for the DB2 LUW database.

  If ARCHIVELOG is not enabled, perform the following steps:

  1. Connect to the database.

     db2 connect to ${db_name}
     

  2. Modify the directory of archive logs.

     db2 update db cfg for ${db_name} using LOGARCHMETH1 logpath(${your_logpath})
     

  3. Back up the database.

     db2 backup database ${db_name} to dbbackuppath(${your_logpath})
     

  4. Stop the database.

     db2stop
     

  5. Start the database.

     db2start
     

  6. Connect to the database.

     db2 connect to ${db_name}
     

  7. Manually archive logs.

     db2 archive log for db ${db_name}
     

  8. View archive logs.

     db2 get db cfg|grep LOG
     

• You have enabled DATA CAPTURE CHANGES for the table in the store of the DB2 LUW database.

  You can execute the following statement to enable DATA CAPTURE CHANGES:

  alter table ${table_name} data capture changes
  

• You have enabled LOG_DDL_STMTS for the DB2 LUW database.

  You can execute the following statement to enable LOG_DDL_STMTS:

  db2 update db cfg using LOG_DDL_STMTS YES
  

Limitations

• Limitations on the source database

  Do not perform DDL operations that modify database or table schemas during schema migration or full migration. Otherwise, the data migration task may be interrupted.

• DB2 LUW 9.7, 10.1, 10.5, 11.1, and 11.5 for Linux and AIX are supported.

• When DB2 LUW 9.7.x serves as the source, DDL synchronization is not supported.

• In an ARM CPU architecture, OMS does not support incremental synchronization from a DB2 LUW database to an Oracle-compatible tenant of OceanBase Database.

• The DB2 LUW database can only parse an object whose name consists of letters, underscores (), and digits, begins with a letter or underscore (), and does not contain a DB2 LUW keyword.

• When you migrate data from a DB2 LUW database to an Oracle-compatible tenant of OceanBase Database, tables with a UNIQUE constraint in the DB2 LUW database can be migrated during full migration and incremental synchronization.

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

• A column with a UNIQUE constraint cannot be null. Otherwise, data inconsistency may occur. Multiple null values are allowed in the same column with a UNIQUE constraint in OceanBase Database: null!=null. However, a column with a UNIQUE constraint in the DB2 LUW database cannot be null. A unique index allows null values, but null=null.

  For example, the unique (c1, c2) (null, null) index of OceanBase Database can be inserted multiple times, while a UNIQUE constraint of the DB2 LUW database does not allow null values. If a unique index is used, (null, null) can be inserted only once.

  Therefore, incompatibility occurs due to null values when OceanBase Database uses unique indexes. Do not use unique keys that allow null columns. Otherwise, errors can occur during schema migration. During incremental synchronization, a NOT NULL constraint is added to the corresponding column, and an error occurs when a null value is written to the column.

  In addition, if you create a unique index in OceanBase Database during DDL synchronization, make sure that all columns with unique indexes are not null. Otherwise, the DB2 LUW database returns an error.

• The user for parsing DB2 LUW database logs must have the sysadm privilege on the corresponding schema. Otherwise, the user cannot obtain logs.

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

Considerations

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

• When LOB-type data in the DB2 LUW database is updated, a large number of row migrations for logs are performed compared with common scenarios. If an unknown combination of row migrations causes an unexpected exit of the store, retain the logs for OceanBase Technical Support.

• Do not use the UPDATE operation to change the primary key. Otherwise, data inconsistency may occur during row migration.

• The DB2 LUW database is mainly used to pull uncompressed logs for testing. The stability of pulling compressed logs has not been verified. Therefore, pull compressed logs with caution.

• Retain logs of the DB2 LUW database and OceanBase Database for at least three days to prepare for a possible pullback in case of exceptions.

• 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 increment.

  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 a NOT NULL constraint is added to the schema of the target Oracle-compatible tenant of OceanBase Database, null strings generated by the source DB2 LUW database cannot be written to the target.

• In a task for reverse increment from a DB2 LUW database to an Oracle-compatible tenant of OceanBase Database of a version earlier than V3.2.x, if the source table is a multi-partition table with a global unique index and you update the values of the partition key of the table, data may be lost during migration.

• If the RENAME operation is performed during DDL synchronization and the source or target table is not in the synchronization list, the RENAME operation is ignored. After the RENAME operation is completed, restart full verification. The full verification will fail because the renamed table is not synchronized to the target database.

• When DDL synchronization is disabled, if you change the unique index in the target database, you must restart the Incr-Sync component. Otherwise, the data in the source and target databases may be inconsistent.

• In multi-table aggregation scenarios:

  • We recommend that you configure the mappings between the source and target databases by specifying 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 you select only Incremental Synchronization when you create the data migration task, OMS requires that the archive logs in the source database be retained for more than 48 hours.

  ​If you select Full Migration and Incremental Synchronization when you create the 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 the source and target table objects differ only in capitalization of their names, the data migration result may not be as expected because the object names in the source or target database are case-insensitive.

• At present, the data migration task does not support tables without a non-null unique key. To avoid duplicate data in case of task restart and other exceptions, we recommend that you configure a non-null unique key for each table.

Data type mappings

Conversion rules for schema migration

Limitations

• The maximum timestamp precision of a DB2 LUW database is 12, while that of an Oracle-compatible tenant of OceanBase Database is 9. Therefore, the data is truncated when it is migrated from a DB2 LUW database to an Oracle-compatible tenant of OceanBase Database. The data that will be truncated cannot be used as the primary key or unique key.

• Length limits

  • The data of the CHAR or BINARY type cannot exceed 255 bytes in length in a DB2 LUW database. If the data written to the Oracle-compatible tenant of OceanBase Database during reverse synchronization exceeds 255 bytes in length, an error is returned for the data migration task.

  • The data of the VARCHAR or BINARY type cannot exceed 32 KB in length in a DB2 LUW database. If the data of the VARCHAR or BINARY type written to an Oracle-compatible tenant of OceanBase Database exceeds 32 KB, OMS returns an error for the data migration task.

  • The Decimal(dp, ds) type in a DB2 LUW database is equivalent to the NUMBER type in an Oracle-compatible tenant of OceanBase Database. The length of dp cannot exceed 31 and must be greater than or equal to that of ds.

    The number written to an Oracle-compatible tenant of OceanBase Database cannot exceed the maximum allowed number. By default, the data of the NUMBER, INT, SMALLINT, and NUMBER(*, s) types is 38 bytes in length in an Oracle-compatible tenant of OceanBase Database. You need to explicitly define NUMBER(p,s) to a length that is compatible with the business application and the source and target databases.

• Data type limitations

  • When a data type in a DB2 LUW database is converted to a LOB type in an Oracle-compatible tenant of OceanBase Database, the LOB-type data cannot exceed 48 MB in size.

  • The data of the TIME type in a DB2 LUW database cannot be migrated as the partition key.

  • The data of the XML type is not supported.

  • We recommend that you do not use CODEUNITS16 or CODEUNITS32 to define or store multi-byte data of the NCHAR, GRAPHIC, or other types.

  • The default value of the BLOB-type data cannot be modified.

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 name of the migration task.

   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 task name must be a unique identifier in the OMS system.

3. In the Select Source and Target step, configure the parameters.

   

   Parameter	Description
   Source	If you have created a DB2 LUW 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, see Create a DB2 LUW data source. Notice The column specified as the unique key in a DB2 LUW database must have the NOT NULL constraint.
   Target	If you have created a data source for the Oracle-compatible tenant of OceanBase Database, which can be a physical data source, a public cloud OceanBase data source, or a standalone 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 the parameters, see Create a physical OceanBase data source, Create a public cloud OceanBase data source, or Create a standalone OceanBase data source.
   Tag (Optional)	Click the text box and select a 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 tasks.

4. Click Next. In the Select Migration Type step, specify the migration types for the migration task.

   

   Options for Migration Type are Schema Migration, Full Migration, Incremental Synchronization, 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 target database. Temporary tables are automatically filtered out.
   Full migration	After a full migration task is started, OMS migrates existing data of tables in the source database to corresponding tables in the target database. If you select Full Migration, we recommend that you use the RUNSTATS statement to collect the statistics of the DB2 LUW database before data migration.
   Incremental synchronization	Changed data in the source database is synchronized to the corresponding tables in the target database after an incremental synchronization task starts. Supported data changes are data addition, modification, and deletion. Options for Incremental Synchronization are DML synchronization and DDL synchronization. Select the options as needed. For more information, see Configure DDL/DML synchronization. Incremental Synchronization has the following limitations: If OMS for ARM is used, incremental synchronization is not supported. If you select DDL synchronization, when you perform a DDL operation that cannot be synchronized by OMS in the source database, data migration may be interrupted. If the DDL operation creates a new column, we recommend that you set the column to NULL. Otherwise, data migration may be interrupted.
   Reverse increment	When a reverse increment task starts, OMS migrates the data changed in the target database after the business switchover back to the source database in real time. Generally, incremental synchronization configurations are reused for reverse increment. You can also customize the configurations for reverse increment as needed. You cannot select Reverse Increment in the following cases: Multi-table aggregation is involved. Multiple source schemas map to the same target schema.

5. (Optional) Click Next.

   If you have selected Reverse Increment without configuring the related parameters for the target Oracle-compatible tenant of OceanBase Database, the Add Data Source Information dialog box appears, prompting you to configure related parameters. For more information about the parameters, see Create a physical OceanBase data source, Create a public cloud OceanBase data source, or Create a standalone OceanBase data source.

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

6. Click Next. In the Select Migration Objects step, specify the migration objects for the migration task.

   You can select Specify Objects or Match by Rule to specify the migration objects. The following procedure describes how to specify migration objects by using the Specify Objects option. For information about the procedure for specifying migration objects by using the Match by Rule option, see Configure matching rules.

   Notice

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

   • If you have selected DDL Synchronization in the Select Migration Type step, we recommend that you select Match by Rule to specify migration objects. This way, all new objects that meet the specified rules will be synchronized. If you select Specify Objects to specify migration objects, new or renamed objects will not be synchronized.

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

   

   1. In the Select Migration Objects section, select Specify Objects.

   2. In the Source Object(s) list, select the objects to be migrated. You can select tables and views of one or more databases as the migration objects.

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

   OMS also allows you to import objects by using text, rename objects, configure row filters, select columns, and remove one or all objects to be migrated.

   Note

   When you select Match by Rule to specify migration objects, object renaming is implemented based on the syntax of the specified matching rules. In the operation area, you can only set filter conditions. For more information, see Configure matching rules.

   Operation	Steps
   Import objects	In the Target Object(s) list, 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 objects	OMS allows you to rename migration objects. For more information, see Rename a migration or synchronization object.
   Configure settings	OMS allows you to configure row filters 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 Use SQL conditions to filter data. 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 objects to be migrated to the target database during data mapping. To remove one migration object: In the Target Object(s) list, move the pointer over the target object and click Remove. To remove all migration objects: In the Target Object(s) list, click Remove All in the upper-right corner. In the dialog box that appears, click OK.

7. Click Next. In the Migration Options step, configure the parameters.

   • Schema migration

     The following parameters are displayed only if you have selected 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 it in the Schema Migration tab on 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 option becomes available only after full migration is selected).

   • Full migration

     The following parameters are displayed only if you have selected 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 values specified here are only for throttling. The actual full migration performance is subject to factors such as the settings of the source and target databases and the instance specifications.
     Full Migration Resource Configuration	You can select Small, Medium, or Large to use the corresponding default values of Read Concurrency, Write Concurrency, and Memory. You can also customize the resource configurations for full migration. By setting the resource configuration for the Full-Import component, you can limit the resource consumption of a task in the full migration phase. Notice In the case of custom configurations, 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. 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 following parameters are displayed only if you have selected 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 values specified here are only for throttling. The actual incremental synchronization performance is subject to factors such as the settings of 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. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.
     Incremental Data Write Resource Configuration	You can select Small, Medium, or Large to use the corresponding default values of Write Concurrency and Memory. You can also customize the resource configurations for incremental data writes. By setting the resource configuration for the Incr-Sync component, you can limit the resource consumption of a task in data writes in the incremental synchronization stage. Notice In the case of custom configurations, 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 following parameters are displayed only if you have selected Reverse Increment in the Select Migration Type step. The parameters for reverse increment are consistent with those for incremental synchronization. You can select Reuse Incremental Synchronization Configuration in the upper-right corner.

     

   • Advanced options

     The following parameters are displayed only if the target is an Oracle-compatible tenant of OceanBase Database V4.3.0 or later and you have selected Schema Migration or DDL synchronization for Incremental Synchronization in the Select Migration Type step.

     

     This parameter specifies the storage type for target table objects during schema migration or incremental synchronization. The storage types supported for target table objects are Default, Row Storage, Column Storage, and Hybrid Row-Column Storage. 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.

   If the parameter settings on the page cannot meet your requirements, you can click Parameter Configuration in the lower part of the page to configure more specific settings. You can also reference an existing task or component template.

   

8. Click Precheck to start a precheck on the data migration task.

   During the precheck, OMS checks the read and write privileges of the database users and the network connectivity of the databases. A data migration task 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 issue and then perform the precheck again.

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

9. Click Start Task. If you do not need to start the task now, click Save to go to the details page of the task. You can start the task later as needed.

   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.

   OMS allows you to modify the migration objects when the data migration task is running. For more information, see View and modify migration objects. After the data migration task is started, it is executed based on the selected migration types. For more information, see the View migration details section in View details of a data migration task.