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

This topic describes how to use OceanBase Migration Service (OMS) to migrate data from an Oracle database to a MySQL tenant of OceanBase Database, which can be a physical data source or an ApsaraDB for OceanBase data source.

Background

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

The Oracle 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 the OceanBase database.

• You have enabled archivelog for the source Oracle instance and switched the logfile before OMS starts incremental data replication.

• You have installed LogMiner in the source Oracle instance, and LogMiner runs properly.

  LogMiner enables you to obtain data from the archive logs of the Oracle instance.

• You have created dedicated database users in the source Oracle 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.

• You have made sure that the Oracle instance has enabled the database-level or table-level supplemental logging feature.

• If you enable supplemental logging of the primary key and unique key at the database level, when a large number of unnecessary logs are generated by tables that do not need to be synchronized, the pressure on LogMiner Reader to fetch logs and on the Oracle database increases. Therefore, you can enable only the table-level supplemental_log of the primary key and unique key for Oracle databases in the OMS console. However, if you specify extract-transform-load (ETL) options to filter columns other than the primary key and unique key columns when you create a migration project, enable supplemental logging for the corresponding columns or all columns.

• Clock synchronization (such as the NTP service) is required between an Oracle server and the OMS server to avoid data risks. For an Oracle RAC, clock synchronization is also required between Oracle instances.

Limitations

• Limitations on the source database

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

• At present, Oracle Database 11g, 12c, 18c, and 19c are supported. Oracle Database 12c and later provide container databases (CDBs) and pluggable databases (PDBs).

• When you use OMS to migrate data from an Oracle database to a MySQL tenant of OceanBase Database, DDL synchronization is not supported.

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

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

• OMS supports the migration of only objects whose database name, table name, and column name are ASCII-encoded and do not contain special characters. The special characters are spaces, line breaks, and the following characters: . | " ' ` ( ) = ; / & \.

• In reverse incremental migration from an Oracle database to a MySQL tenant of OceanBase Database, a database name or table name in the source database cannot contain a lowercase letter. Otherwise, the check items of the reverse incremental migration will fail the precheck.

• The data transmission service can parse up to 5 TB of incremental logs of Oracle databases per day.

• You cannot create a database object whose name exceeds 30 bytes in length in an Oracle database of version 11g or earlier. In the reverse incremental migration step, you cannot create database objects with an object name longer than this length limit in the MySQL tenant of OceanBase Database.

• OMS does not support the migration of database objects, such as schemas, tables, and columns, whose name exceeds 30 bytes in length from an Oracle database of version 12c or later.

• OMS does not support some UPDATE statements in the source Oracle database. For example, the following UPDATE statement is not supported:

  UPDATE TABLE_NAME SET KEY=KEY+1;
  

  In the preceding example, TABLE_NAME is the table name, and KEY is a primary key column of the NUMERIC type.

Considerations

• When the Oracle database is in standby database only or primary/standby databases mode, if the number of instances that run on the primary Oracle database differs from that on the standby database, incremental logs of some instances may not be pulled. You need to manually set the parameters of the Store component to specify the instances for which incremental logs are to be pulled from the standby database. The procedure is as follows:

  1. Stop the Store component as soon as it starts.

  2. On the Update Configuration page of the Store component, add the deliver2store.logminer.instance_threads parameter and specify the instances for which logs are to be pulled.

     Separate multiple threads with vertical bars (|), for example, 1|2|3. For more information about how to update a store component, see Update a store component.

  3. Restart the Store component.

  4. Wait five minutes, and then run the grep 'log entries from' connector/connector.log command to check the instances for which logs are pulled. The thread field indicates the instances for which logs are pulled.

• If you need to synchronize incremental data from an Oracle database, we recommend that you restrict the size of a single archive file in the Oracle database to within 2 GB. An excessively large archive file may incur the following risks:

  • The log pulling time increases not in proportion to the size of a single archive file, but much more sharply.

  • When the Oracle database is in standby database only or primary/standby databases mode, the incremental data is pulled from the standby database. In this case, only archive files can be pulled. An archive file is pulled after it is generated. A larger archive file means a longer delay before the archive file is processed, and a longer time for processing the archive file.

  • In addition, a larger size of a single archive file means larger memory required by the Store component under the same data pulling concurrency.

• The archive files must be stored for more than two days in the Oracle database. Otherwise, in the case of a sharp increase in the number of archive files or an exception in the Store component, restoration may fail due to the lack of required archive files.

• If the source Oracle database is sensitive to trailing spaces, right-trimming is forcibly performed on data of the CHAR or VARCHAR type in the destination MySQL tenant of OceanBase Database, which results in data inconsistency.

• If a DML operation is performed to exchange primary keys in the source Oracle database, errors occur when OMS parses logs. This causes data loss when data is migrated to the destination database. Here is a sample DML statement that exchanges primary keys:

  UPDATE test SET c1=(CASE WHEN c1=1 THEN 2 WHEN c1=2 THEN 1 END) WHERE c1 IN (1,2);
  

• OMS allows you to migrate data from an Oracle instance whose character set is AL32UTF8, AL16UTF16, ZHS16GBK, or GB18030. 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 you select a migration mode that supports incremental synchronization and reverse incremental migration, and an exception occurs when OMS pulls the incremental data from a standby Oracle database, you can run the ALTER SYSTEM SWITCH LOGFILE command in the primary database to handle the exception.

• 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 a table without a primary key from an Oracle database to an Oracle tenant of OceanBase Database, do not perform any operations on any table that may change the ROWID, such as data import and export, Alter Table, FlashBack Table, and partition splitting or compaction.

• In a project for reverse incremental migration from an Oracle database to a MySQL 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 partitioning key of the table, data may be lost during migration.

• If the primary key or unique key, which serves as a verification field, contains data of the INTERVAL type, you must set filter.verify.inmod.tables to the in mode for the table. Otherwise, the verification result is inaccurate.

  You can set or update the value of the filter.verify.inmod.tables parameter of the Full-Verification component to .*;.*;.*. For more information, see Update the configurations of a Full-Verification component.

• A function similar to update current_timestamp exists in the time type field of a MySQL tenant of OceanBase Database, which will cause data inconsistency between the source and destination databases.

• Check whether the migration precision of OMS for columns of data types such as 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.

• 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, drop the unique indexes and pseudocolumns from the destination. If you do not drop 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 will automatically drop hidden columns and unique indexes based on the type of the migration project. For more information, see Mechanisms for handling hidden columns.

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

• Take note of the following points if you want to perform data merge migration:

  • We recommend that you configure the mappings between the source and destination databases by specifying matching rules.

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

• 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 at the destination, if the data types of any columns are not supported by OMS, implicit data type conversion may occur at the destination, 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.

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

  If you select Full Data Migration and Incremental Synchronization when you create a data migration project, OMS requires that the archive logs in the source database be retained for at least 7 days. Otherwise, the data migration project will fail or the data in the source and destination databases will be inconsistent because OMS cannot obtain incremental logs.

Check and modify the system configurations of the Oracle instance

Perform the following operations:

1. Enable ARCHIVELOG for the source Oracle database.

2. Enable supplemental logging for the source Oracle database.

3. (Optional) Set the system parameters of the Oracle database.

Enable ARCHIVELOG for the source Oracle database.

SELECT log_mode FROM v$database;

The value of the log_mode field must be archivelog. Otherwise, perform the following steps to change it:

1. Run the following commands to enable ARCHIVELOG:

   SHUTDOWN IMMEDIATE;
   STARTUP MOUNT;
   ALTER DATABASE ARCHIVELOG;
   ALTER DATABASE OPEN;
   

2. Run the following command to view the path and quota of archive logs.

   View the path and quota of the recovery file. We recommend that you set the db_recovery_file_dest_size parameter to a relatively large value. After you enable ARCHIVELOG, you need to regularly clear the archive logs by using Recovery Manager (RMAN) or other methods.

   SHOW PARAMETER db_recovery_file_dest;
   

3. Change the quota of archive logs as needed.

   ALTER SYSTEM SET db_recovery_file_dest_size =50G SCOPE = BOTH;
   

Enable supplemental logging for the source Oracle database.

LogMiner Reader allows you to enable only table-level supplemental logging for an Oracle database. If you create a table in the source Oracle database during the migration and the table needs to be migrated, you must enable supplemental logging for the primary key and unique key before you perform DML operations. Otherwise, OMS returns an exception indicating incomplete logs.

If the indexes are inconsistent between the source and target databases, the extract-transform-load (ETL) results are not as expected, or the migration performance of partitioned tables deteriorates, you need to perform the following operations:

• Add the database-level or table-level supplemental_log_data_pk and supplemental_log_data_ui parameters.

• Enable supplemental logging for columns.

  • Add all columns involved by the primary keys or unique keys in the source and target databases to resolve the problem of index inconsistency between the source and target databases.

  • If an ETL exists, add the ETL column to resolve the problem that the ETL does not meet the expectation.

  • If the target table is a partitioned table, add a partitioning column to resolve the problem that the write performance deteriorates because partition pruning cannot be performed.

  You can execute the following statement to check the addition result:

  SELECT log_group_type FROM all_log_groups WHERE OWNER = '<schema_name>' AND table_name = '<table_name>';
  

  If the check result includes ALL COLUMN LOGGING, the check is passed. Otherwise, check whether the ALL_LOG_GROUP_COLUMNS table contains all preceding columns.

  Here is a sample statement for enabling supplemental logging for columns:

  ALTER TABLE <table_name> ADD SUPPLEMENTAL LOG GROUP <table_name_group> (c1, c2) ALWAYS;
  

The following table describes the possible risks and solutions when you perform DDL operations in a running data migration project.

LogMiner Reader uses one of the following two methods to check whether supplemental logging is enabled. If not, LogMiner Reader exits.

• Enable supplemental_log_data_pk and supplemental_log_data_ui at the database level.

  Run the following commands to check whether the supplemental logging feature is enabled. If the returned values are both YES, supplemental logging is enabled.

  SELECT supplemental_log_data_pk, supplemental_log_data_ui FROM v$database;
  

  Otherwise, perform the following steps:

  1. Execute the following statement to enable the supplemental logging feature.

     ALTER DATABASE ADD supplemental log DATA(PRIMARY KEY, UNIQUE) columns;
     

  2. After you enable supplemental logging, perform a switchover to the ARCHIVELOG mode twice and wait at least 5 minutes before you start a project. For an Oracle RAC, perform a switchover for the instances alternately.

     ALTER SYSTEM SWITCH LOGFILE;
     

     The reason for performing a switchover to the ARCHIVELOG mode twice is as follows:

     When the Store component locates the start time for pulling log files, the database is rolled back by zero to two archive logs based on the specified timestamp. Therefore, after you enable the supplemental log feature, you need to perform a switchover to the ARCHIVELOG mode twice to prevent the Store component from pulling the logs that are generated before the specified timestamp. Otherwise, the Store component exits unexpectedly.

     The reason for alternately performing the ARCHIVELOG switchover among multiple instances in a RAC system:

     In an Oracle RAC system, if you perform the ARCHIVELOG switchover multiple times on one instance, when you perform the ARCHIVELOG switchover on the next instance, the latter instance may pull the logs that are generated before supplemental logging is enabled.

• Enable supplemental_log_data_pk and supplemental_log_data_ui at the table level.

  1. Execute the following statement to confirm whether supplemental_log_data_min is enabled at the database level:

     SELECT supplemental_log_data_min FROM v$database;
     

     If the returned value is YES or IMPLICIT, supplemental logging is enabled.

  2. Execute the following statement to check whether the table-level supplemental logging is enabled for the tables to be synchronized.

     SELECT log_group_type FROM all_log_groups WHERE OWNER = '<schema_name>' AND table_name = '<table_name>';
     

     Each type of supplemental logging returns one row. The results must contain ALL COLUMN LOGGING or both PRIMARY KEY LOGGING and UNIQUE KEY LOGGING.

     If the table-level supplemental logging is not enabled, execute the following statement.

     ALTER TABLE table_name ADD SUPPLEMENTAL LOG DATA (PRIMARY KEY, UNIQUE) COLUMNS;
     

  3. After you enable supplemental logging, perform a switchover to the ARCHIVELOG mode twice and wait at least 5 minutes before you start a project. For an Oracle RAC, perform a switchover for the instances alternately.

     ALTER SYSTEM SWITCH LOGFILE;
     

(Optional) Set the system parameters of the Oracle database

We recommend that you set the _log_parallelism_max parameter of the Oracle database to 1. The default value is 2.

1. Query the value of the _log_parallelism_max parameter by using either of the following methods:

   • Method 1

     SELECT NAM.KSPPINM,VAL.KSPPSTVL,NAM.KSPPDESC FROM SYS.X$KSPPI NAM,SYS.X$KSPPSV VAL WHERE NAM.INDX= VAL.INDX AND NAM.KSPPINM LIKE '_%' AND UPPER(NAM.KSPPINM) LIKE '%LOG_PARALLEL%';
     

   • Method 2

     SELECT VALUE FROM v$parameter WHERE name = '_log_parallelism_max';
     

2. Modify the value of _log_parallelism_max. You can execute either of the following statements as needed:

   • Oracle RAC

     ALTER SYSTEM SET "_log_parallelism_max" = 1 SID = '*' SCOPE = spfile;
     

   • Non-Oracle RAC

     ALTER SYSTEM SET "_log_parallelism_max" = 1 SCOPE = spfile;
     

   When you modify the value of _log_parallelism_max in Oracle 10g, if the error message write to SPFILE requested but no SPFILE specified at startup is returned, execute the following statements:

   CREATE SPFILE FROM PFILE;
   SHUTDOWN IMMEDIATE;
   STARTUP;
   SHOW PARAMETER SPFILE;
   

3. After you modify the value of _log_parallelism_max, restart the instance, perform a switchover to the ARCHIVELOG mode twice, and wait more than five minutes before you start a project.

Data type mappings

Procedure

1. Create a data 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, 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 (Optional)	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 an Oracle 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 an Oracle data source.
   Destination	If you have created a MySQL tenant of OceanBase Database data source, which can be a physical data source or an ApsaraDB for OceanBase 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 or Create a public cloud OceanBase data source.

3. Click Next. On the Select Migration Type page, configure the following parameters.

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

   Migration type	Description
   Schema migration	When a schema migration task starts, OMS migrates the definitions of data objects, such as tables, indexes, constraints, comments, and views, from the source database to the destination database. Temporary tables are automatically filtered out. The limitations on using schema migration are as follows: The data of the NUMERIC type in the MySQL tenant of OceanBase Database cannot serve as a partitioning key. During schema migration of a partitioned table without a primary key, the data of the NUMBER or INT type in the partitioning column of the Oracle database is converted to data of the NUMERIC type, resulting in an error. During schema migration, the data of the TIMESTAMP type (with a precision of 9) in the Oracle database is converted to data of the DATETIME type (with a precision of 6) in the MySQL tenant of OceanBase Database. Precision loss occurs. During schema migration, the data of the BINARY_FLOAT type in the Oracle database is converted to data of the DOUBLE type in the MySQL tenant of OceanBase Database. Precision loss may occur during reverse incremental migration.
   Full migration	When a full migration task starts, OMS migrates the existing data from tables in the source database to the corresponding tables in the destination database. If you select Full Migration, we recommend that you use the GATHER_SCHEMA_STATS or GATHER_TABLE_STATS statement to collect the statistics of the Oracle database before data migration.
   Incremental synchronization	When an incremental synchronization task starts, OMS synchronizes changed data in the source database to the corresponding tables in the destination database. Data changes are data addition, modification, and deletion. Incremental Synchronization supports the following DML operations: Insert, Delete, and Update. You can select the operations based on your business needs. For more information, see DML filtering. If the data in all columns in the tables of the Oracle database to be migrated are of an LOB type (BLOB, CLOB, or NCLOB), Incremental Synchronization is not supported.
   Full verification	After the full data migration and incremental data synchronization are completed, OMS 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 the Oracle 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.
   Reverse incremental migration	When a reverse incremental migration task starts, OMS migrates the data changed in the destination database after the business switchover back to the source database in real time. You cannot select Reverse Increment in the following cases: Data merge migration that involves multiple tables is enabled. Multiple source schemas map to the same destination schema.

4. Click Next. On the Select Migration Objects page, specify 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.

     • OMS automatically filters out unsupported tables.

     OMS also allows you to import objects from text, rename objects, set row filters, view column information, and remove a single object or all objects to be migrated.

     

     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 objects	OMS allows you to rename the migration objects. For more information, see Rename a migration or synchronization object.
     Configure 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 one or all objects	During data mapping, OMS allows you to remove one or more selected objects to be migrated or synchronized to the destination. 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.

     When the source database is an Oracle database, if row filtering is enabled for columns other than the primary key and unique key columns, enable supplemental_log for the corresponding columns or all columns.

     Execute the following statement to enable supplemental_log for the corresponding columns:

     ALTER TABLE table_name ADD SUPPLEMENTAL LOG GROUP log_group_name (column1, column2, column3) ALWAYS;
     

     Execute the following statement to enable supplemental_log for all columns:

     -- Enable database-level supplemental_log:
     ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS;
     -- Enable table-level supplemental_log:
     ALTER TABLE table_name ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS;
     

   • Select Match Rules. For more information, see Configure matching rules for migration objects.

5. Click Next. On the Migration Options page, configure the following parameters.

   • Full migration

     The following parameters are displayed only if you have selected Full Data Migration on the Select Migration Type page.

     

     Parameter	Description
     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. Through resource configuration for the Full-Import component, you can limit the resource consumption of a project in the full migration phase. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.
     Processing Strategy When Destination Table Has Records	Valid values: Ignore and Stop Migration. If you select Ignore, when the data to be written conflicts with the existing data of a destination table, OMS logs the conflicting data while retaining the existing data. Notice If you select Ignore, data is pulled in IN mode for full verification. In this case, the scenario where the destination contains more data than the source 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 ignores this error and continues to migrate data. Proceed with caution.
     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 Data Migration on the Select Migration Type page. Only non-unique key indexes can be created after the migration is completed. OceanBase Database V1.x does not support the post-indexing feature.

     If post-indexing is allowed, we recommend that you adjust the parameters based on the hardware conditions of your OceanBase database and the current business traffic.

     • If you use OceanBase Database V4.x, adjust the following parameters of the sys tenant and business tenants by using a 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 V2.x or 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 parameters are displayed only if you have selected Incremental Synchronization on the Select Migration Type page.

     

     Parameter	Description
     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. Through resource configuration for the Store component, you can limit the resource consumption of a project in log pull in the incremental synchronization phase. 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 write. Through resource configuration for the Incr-Sync component, you can limit the resource consumption of a project in data writes in the incremental synchronization phase. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.
     Incremental Record Retention Time	The duration that incremental parsed files are cached in OMS. A longer retention period results in more disk space occupied by the Store component.
     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.

   • Reverse incremental migration

     The following parameters are displayed only if you have selected Reverse Increment on the Select Migration Type page. The parameters for reverse incremental migration are consistent with those for incremental synchronization. You can select Reuse Incremental Synchronization Configuration in the upper-right corner.

     

   • Full verification

     The following parameters are displayed only if you have selected Full Verification on the Select Migration Type page.

     

     Parameter

     Description

     Full Verification Resource Configuration

     You can select Small, Medium, or Large to use the corresponding default values of Read Concurrency and Memory. You can also customize the resource configurations for full verification. Through resource configuration for the Full-Verification component, you can limit the resource consumption of a project in the full verification phase. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.

   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 project or component template.

   

6. Click Precheck to start a precheck on the data migration project.

   During the precheck, 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.

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

   • Click Skip in the Actions column of a failed precheck item. In the dialog box that appears, you can view the prompt for the consequences of the operation and click OK.

7. 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 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.