Migrate data from a PolarDB for MySQL cluster to a self-managed Oracle database - Data Transmission Service

This topic describes how to use Data Transmission Service (DTS) to migrate data from a PolarDB for MySQL cluster to a self-managed Oracle database.

Prerequisites

The destination self-managed Oracle database is created and the available storage space of the destination Oracle database is larger than the total size of the data in the source PolarDB for MySQL cluster.
The self-managed Oracle database is connected to Alibaba Cloud by using a virtual private cloud (VPC) if the database is an Oracle Real Application Cluster (RAC) database. Each Single Client Access Name (SCAN) IP of the Oracle RAC database and the virtual IP address (VIP) of each node are connected to the VPC, and routing rules are configured. This ensures that DTS tasks can run as expected. For more information, see Connect an on-premises database to Alibaba Cloud and Connect a data center to DTS by using VPN Gateway.

Limits

Note

During schema migration, DTS migrates foreign keys from the source database to the destination database.
During full data migration and incremental data migration, DTS temporarily disables the constraint check and cascade operations on foreign keys at the session level. If you perform the cascade and delete operations on the source database during data migration, data inconsistency may occur.

Category	Description
Limits on the source database	The server to which the source database belongs must have sufficient outbound bandwidth. Otherwise, the data migration speed decreases. The tables to be migrated must have PRIMARY KEY or UNIQUE constraints, and all fields must be unique. Otherwise, the destination database may contain duplicate data records. If you select tables as the objects to be migrated and you need to edit tables, such as renaming tables or columns in the destination database, up to 1,000 tables can be migrated in a single data migration task. If you run a task to migrate more than 1,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to migrate the tables or configure a task to migrate the entire database. If you need to migrate incremental data, the binary logging feature must be enabled and the loose_polar_log_bin parameter must be set to on. Otherwise, error messages are returned during precheck and the data migration task cannot be started. For more information about how to enable the binary logging feature and set the loose_polar_log_bin parameter, see Enable binary logging and Modify parameters. Note If you enable the binary logging feature for a PolarDB for MySQL cluster, you are charged for the storage space that is occupied by binary logs. For an incremental data migration task, the binary logs of the source database must be retained for more than 24 hours. For a full data and incremental data migration task, the binary logs of the source database must be retained for at least seven days. Otherwise, Data Transmission Service (DTS) may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. After full data migration is complete, you can set the retention period to more than 24 hours. Make sure that you set the retention period of binary logs based on the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not guarantee service reliability or performance. Limits on operations to be performed on the source database: During schema migration and full data migration, do not perform DDL operations to change the schemas of databases or tables. Otherwise, the data migration task fails. If you perform only full data migration, do not write data to the source database during data migration. Otherwise, data inconsistency may occur between the source and destination databases. To ensure data consistency, we recommend that you select schema migration, full data migration, and incremental data migration as the migration types.
Other limits	Read-only nodes of the source PolarDB for MySQL cluster cannot be migrated. If the database is an Oracle RAC database connected over Express Connect, VPN Gateway, Smart Access Gateway, Database Gateway, or Cloud Enterprise Network (CEN), or hosted on an Elastic Compute Service (ECS) instance, you can use a single VIP rather than a SCAN IP when you configure the database. After you specify the VIP, node failover is not supported for the Oracle RAC database. Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. During full data migration, DTS uses read and write resources of the source and destination databases. This may increase the loads on the database servers. During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data migration is complete, the tablespace of the destination database is larger than that of the source database. You must make sure that the precision settings for columns of the FLOAT or DOUBLE data type meet your business requirements. DTS uses the `ROUND(COLUMN,PRECISION)` function to retrieve values from columns of the FLOAT or DOUBLE data type. If you do not specify a precision, DTS sets the precision for the FLOAT data type to 38 digits and the precision for the DOUBLE data type to 308 digits. DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch workloads to the destination database, stop or release the data migration task. You can also execute the `REVOKE` statement to revoke the write permissions from the accounts used by DTS to access the destination database. Otherwise, the data in the source database overwrites the data in the destination database after a failed task is resumed.
Special cases	DTS executes the CREATE DATABASE IF NOT EXISTS `test` statement in the source database as scheduled to move forward the binary log file position.

Billing

Migration type	Instance configuration fee	Internet traffic fee
Schema migration and full data migration	Free of charge.	Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

SQL operations that can be incrementally migrated

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE
DDL	CREATE TABLE, ALTER TABLE, DROP TABLE, RENAME TABLE, and TRUNCATE TABLE ADD COLUMN, DROP COLUMN, MODIFY COLUMN, and RENAME COLUMN CREATE INDEX and DROP INDEX

Permissions required for database accounts

Database	Required permission	References
Source PolarDB for MySQL cluster	Read permissions on the objects to be migrated	Create and manage a database account
Destination Oracle database	Permissions of the schema owner	CREATE USER and GRANT

Procedure

Go to the Data Migration Tasks page.
1. Log on to the Data Management (DMS) console.
2. In the top navigation bar, click DTS.
3. In the left-side navigation pane, choose DTS (DTS) > Data Migration.
Note
- Operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Customize the layout and style of the DMS console.
- You can also go to the Data Migration Tasks page of the new DTS console.
From the drop-down list next to Data Migration Tasks, select the region in which the data migration instance resides.
Note
If you use the new DTS console, you must select the region in which the data migration instance resides in the upper-left corner.

Click Create Task. In the Create Task wizard, configure the source and destination databases.

Section	Parameter	Description
N/A	Task Name	The name of the DTS task. DTS automatically generates a task name. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to specify a unique task name.
Source Database	Select an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	Select whether to use an existing instance. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the database.
	Database Type	The type of the source database. Select PolarDB for MySQL.
	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source PolarDB for MySQL cluster resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
	PolarDB Cluster ID	The ID of the source PolarDB for MySQL cluster.
	Database Account	The database account of the source PolarDB for MySQL cluster. For more information about the permissions that are required for the database account, see the Permissions required for database accounts section of this topic.
	Database Password	The password of the database account.
	Encryption	Specifies whether to encrypt the connection to the source database. You can set this parameter based on your business requirements. For more information about the SSL encryption feature, see Configure SSL encryption.
Destination Database	Select an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	Select whether to use an existing instance. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the database.
	Database Type	The type of the destination database. Select Oracle.
	Access Method	The access method of the destination database. In this example, Self-managed Database on ECS is selected. Note If you select another access method, you must set up the environment that is required for the self-managed Oracle database. For more information, see Preparation overview.
	Instance Region	The region in which the destination Oracle database resides.
	ECS Instance ID	The ID of the ECS instance that hosts the destination Oracle database.
	Port Number	The service port number of the destination Oracle database. Default value: 1521.
	Oracle Type	The architecture of the destination Oracle database. Valid values: Non-RAC Instance: If you select this value, you must configure the SID parameter. RAC or PDB Instance: If you select this value, you must configure the Service Name parameter. In this example, RAC or PDB Instance is selected and the Service Name parameter is configured.
	Database Account	The database account of the destination Oracle database. For more information about the permissions that are required for the database account, see the Permissions required for database accounts section of this topic.
	Database Password	The password of the database account.

In the lower part of the page, click Test Connectivity and Proceed.
If the source or destination database instance is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the IP address whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Computing Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance. If the source or destination database is a self-managed database that is deployed on a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the IP address whitelist of the database to allow DTS to access the database. For more information, see the "CIDR blocks of DTS servers" section of the Add the CIDR blocks of DTS servers topic.
Warning
If the public CIDR blocks of DTS servers are automatically or manually added to the whitelist of a database instance or to the security group rules of an ECS instance, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or security group rules and forbidding unauthorized CIDR blocks, or connecting the database instance to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

Configure the objects to be migrated and the advanced settings.

Parameter	Description
Migration Types	To perform only full data migration, select Schema Migration and Full Data Migration. To ensure service continuity during data migration, select Schema Migration, Full Data Migration, and Incremental Data Migration. Note If you do not select Incremental Data Migration, we recommend that you do not write data to the source database during data migration. This ensures data consistency between the source and destination databases.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that use the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started. Note If the source and destination databases contain identical table names and the tables in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the tables that are migrated to the destination database. For more information, see Map object names. Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to the following potential risks: If the source and destination databases have the same schema, DTS does not migrate data records that have the same primary keys as data records in the destination database. If the source and destination databases have different schemas, only specific columns are migrated or the data migration task fails. Proceed with caution.
Capitalization of Object Names in Destination Instance	The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to make sure that the capitalization of object names is consistent with that of the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.
Source Objects	Select one or more objects from the Source Objects section and click the icon to add the objects to the Selected Objects section. Note You can select columns, tables, or databases as the objects to be migrated. If you select tables or columns as the objects to be migrated, DTS does not migrate other objects, such as views, triggers, or stored procedures, to the destination database.
Selected Objects	To rename a database, right-click the database in the Selected Objects section. In the Edit Schema dialog box, set the Schema Name parameter to the database name that you want to use in the destination Oracle database. For more information, see Map object names. Note To select the SQL operations that are performed on a specific database or table, right-click the object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to incrementally migrate. For more information, see the SQL operations that can be incrementally migrated section of this topic. To specify WHERE conditions to filter data, right-click a table in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Set filter conditions. If you use the object name mapping feature to rename an object, other objects that depend on the object may fail to be migrated.

Click Next: Advanced Settings to configure advanced settings.

Data Verification Settings
For more information about how to use the data verification feature, see Configure data verification.

Advanced Settings

Parameter	Description
Select the dedicated cluster used to schedule the task	By default, DTS schedules the task to a shared cluster. You do not need to configure this parameter. You can also purchase a dedicated cluster of the specified specifications to run data migration tasks. For more information, see What is a DTS dedicated cluster?
Retry Time for Failed Connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data migration task is started, DTS immediately retries a connection within the retry time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS is reconnected to the source and destination databases within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you specify different retry time ranges for multiple data migration tasks that share the same source or destination database, the value that is specified later takes precedence. When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at the earliest opportunity after the source database and destination instance are released.
The wait time before a retry when other issues occur in the source and destination databases.	The retry time range for other issues. For example, if DDL or DML operations fail to be performed after the data migration task is started, DTS immediately retries the operations within the retry time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set the parameter to a value greater than 10. If the failed operations are successfully performed within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Important The value of the The wait time before a retry when other issues occur in the source and destination databases parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Full Data Migration	Specifies whether to enable throttling for full data migration. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. You can enable throttling for full data migration based on your business requirements. To configure throttling, you must configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only when you select Full Data Migration for the Migration Types parameter.
Enable Throttling for Incremental Data Migration	Specifies whether to enable throttling for incremental data migration. To configure throttling, you must configure the RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only when you select Incremental Data Migration for the Migration Types parameter.
Environment Tag	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements. In this example, no environment tag is selected.
Whether to delete SQL operations on heartbeat tables of forward and reverse tasks	Specifies whether to write SQL operations on heartbeat tables to the source database while the DTS instance is running. Yes: does not write SQL operations on heartbeat tables. In this case, a latency of the DTS instance may be displayed. No: writes SQL operations on heartbeat tables. In this case, specific features such as physical backup and cloning of the source database may be affected.
Configure ETL	Specifies whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.
Monitoring and Alerting	Specifies whether to configure alerting for the data migration task. If the task fails or the migration latency exceeds the specified threshold, the alert contacts receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. If you select Yes, you must also specify the alert threshold and alert contacts. For more information, see the Configure monitoring and alerting for a new DTS task section of the "Configure monitoring and alerting" topic.

Save the task settings and run a precheck.
- To view the parameters to be specified when you call the relevant API operation to configure the DTS task, move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters.
- If you do not need to view or have viewed the parameters, click Next: Save Task Settings and Precheck in the lower part of the page.
Note
- Before you can start the data migration task, DTS performs a precheck. You can start the data migration task only after the task passes the precheck.
- If the task fails to pass the precheck, click View Details next to each failed item. After you troubleshoot the issues based on the error message, you can run a precheck again.
- If an alert is triggered for an item during the precheck:
  If the alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issues. Then, run a precheck again.
  If the alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur and your business may be exposed to potential risks.
Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.

On the Purchase Instance page, configure the Instance Class parameter for the data migration instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Resource Group	The resource group to which the data migration instance belongs. Default value: default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Specifications of data migration instances.

Read and agree to Data Transmission Service (Pay-as-you-go) Service Terms by selecting the check box.
Click Buy and Start to start the data migration task. You can view the progress of the task on the Task Management page of the data migration task.