Migrate data from a PolarDB for MySQL cluster to an AnalyticDB for MySQL V3.0 cluster - Data Transmission Service

This topic describes how to migrate data from a PolarDB for MySQL cluster to an AnalyticDB for MySQL V3.0 cluster by using Data Transmission Service (DTS). After you migrate the data, you can use AnalyticDB for MySQL to build systems such as internal business intelligence (BI) systems, interactive query systems, and real-time report systems.

Prerequisites

The source PolarDB for MySQL cluster is created. For more information, see Purchase a pay-as-you-go cluster and Purchase a subscription cluster.
The destination AnalyticDB for MySQL V3.0 cluster is created. For more information, see Create a cluster.
The available storage space of the destination AnalyticDB for MySQL cluster is larger than the total size of the data in the source PolarDB for MySQL cluster.

Limits


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 migrate 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 in batches, or configure a task to migrate the entire database. The binary logging feature must be enabled. 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. Note For an incremental data migration task, binary logs of the source database must be stored for more than 24 hours. For a full data and incremental data migration task, binary logs of the source database must be stored for at least seven days. After full data migration is complete, you can set the retention period to more than 24 hours. 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. Make sure that you set the retention period of binary logs based on the preceding requirements. Otherwise, the service reliability and performance stated in the Service Level Agreement (SLA) of DTS cannot be achieved. Limits on operations that are 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. During data migration, do not perform DDL operations to add comments. For example, do not execute the `ALTER TABLE table_name COMMENT='Table comment';` statement. 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 between the source and destination databases occurs. To ensure data consistency, we recommend that you select schema migration, full data migration, and incremental data migration as the migration types.
Usage notes	Prefix indexes cannot be migrated. If the source database contains prefix indexes, data may fail to be migrated. Read-only nodes of the source PolarDB for MySQL cluster cannot be migrated. Due to the limits of AnalyticDB for MySQL,if the disk space usage of the nodes in an AnalyticDB for MySQL cluster reaches 80%, the task is delayed and error messages are returned. We recommend that you estimate the required disk space based on the objects to migrate. You must make sure that the destination cluster has sufficient storage space. 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 the read and write resources of the source and destination databases. This may increase the loads of 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 size of used 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 will overwrite the data in the destination database after the task is resumed. 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.

Migration types

Schema migration
DTS migrates the schemas of objects from the source database to the destination database.

Note ApsaraDB RDS for MySQL and AnalyticDB for MySQL are heterogeneous databases. DTS does not ensure that the schemas of the source and destination databases are consistent after schema migration. We recommend that you evaluate the impact of data type conversion on your business. For more information, see Data type mappings between heterogeneous databases.
Full data migration
DTS migrates the historical data of objects from the source database to the destination database.
Incremental data migration
After full data migration is complete, DTS synchronizes incremental data from the source database to the destination database. Incremental data migration ensures the service continuity of self-managed applications during data migration.

SQL operations that can be migrated


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

Warning If the data type of a field in the source table is changed during data migration, an error message is returned and the data migration task is stopped. You can perform the following steps to troubleshoot the issue:

Check whether the data migration task fails because the data type of a field in the source table, such as the customer field, is changed when DTS migrates data to the destination AnalyticDB for MySQL V3.0 cluster.
In the destination AnalyticDB for MySQL V3.0 cluster, create a table named customer_new that has the same schema as the customer table.
Execute the INSERT INTO SELECT statement to copy the data of the customer table and insert the data into the customer_new table. This ensures that the data of the two tables is consistent.
Rename or delete the customer table. Then, change the name of the customer_new table to customer.
Restart the data migration task in the DTS console.

Permissions required for database accounts


Database	Required permission
PolarDB for MySQL	Read permissions on the objects to be migrated
AnalyticDB for MySQL 3.0	Read and write permissions

For more information about how to create and grant permissions to a database account, see the following topics:

PolarDB for MySQL cluster: Create a database account
AnalyticDB for MySQL V3.0 cluster: Create a database account

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 You can also configure the settings by using the new DTS console.
From the drop-down list to the right of Data Migration Tasks, select the region in which your data migration instance resides.

Note If you use the new DTS console, select the region in which your data migration instance resides in the upper-left corner.

Click Create Task. On the page that appears, configure the source and destination databases.

Warning After you select the source and destination instances, we recommend that you read the limits displayed at the top of the page. This helps you create and run the data migration task.


Section	Parameter	Description
N/A	Task Name	The name of the task. DTS automatically generates a task name. We recommend that you specify an informative name to identify the task. You do not need to specify a unique task name.
Source Database	Select Instance	The instance that you want to use. You can choose whether to use an existing instance based on your business requirements. If you use an existing instance, DTS automatically applies the parameter settings of the instance. If you do not use an existing instance, you must set parameters for the source 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.
	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 information about the permissions that are required for the account, see Permissions required for database accounts.
	Database Password	The password of the database account.
Destination Database	Select Instance	The instance that you want to use. You can choose whether to use an existing instance based on your business requirements. If you use an existing instance, DTS automatically applies the parameter settings of the instance. If you do not use an existing instance, you must set parameters for the destination database.
	Database Type	The type of the destination database. Select AnalyticDB for MySQL V3.0.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination AnalyticDB for MySQL V3.0 cluster resides.
	Instance ID	The ID of the destination AnalyticDB for MySQL V3.0 cluster.
	Database Account	The database account of the destination AnalyticDB for MySQL V3.0 cluster. For information about the permissions that are required for the account, see Permissions required for database accounts.
	Database Password	The password of the database account.

In the lower part of the page, click Test Connectivity and Proceed.
Warning
- 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, or is a self-managed database hosted on Elastic Compute Service (ECS), DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the database instance or ECS security group rules. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases. If the source or destination database is a self-managed database on data centers or is from other cloud service providers, you must manually add the CIDR blocks of DTS servers to allow DTS to access the database.
- If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database, Alibaba Cloud database instance, or ECS security group rules, 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 ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
- After the DTS task is complete or released, we recommend that you manually detect and remove the added CIDR blocks from the whitelist of the database, Alibaba Cloud database instance, or ECS security group rules.

Select objects for the task and configure advanced settings.


Parameter	Description
Task Stages	If you want to perform only full data migration, select Schema Migration and Full Data Migration. If you want to ensure service continuity during data migration, select Schema Migration, Full Data Migration, and Incremental Data Migration. Note If Full Data Migration is selected, you can migrate the schema and data of the table that is created by executing the CREATE TABLE statement to the destination database. If Incremental Data Migration is not selected, 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 have the same names as tables in the source database. If the source and destination databases do not contain tables that have the same names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started. Note You can use the object name mapping feature to rename the tables that are migrated to the destination database. You can use this feature if the source and destination databases contain tables that have identical names and the tables in the destination database cannot be deleted or renamed. 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 consistency is not ensured, and your business may be exposed to 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.
DDL and DML Operations to Be Synchronized	The SQL operations to be migrated at the instance level. For more information, see SQL operations that can be migrated. Note To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to synchronize.
Merge Tables	Yes: If you select this value, DTS adds the `__dts_data_source` column to each table to record data sources. For more information, see Enable the multi-table merging feature. No: This value is selected by default. Note If you set this parameter to Yes, all the selected source tables in the task are merged into a single destination table. If you do not need to merge specific source tables, you can create a separate data migration task for these tables. Warning We recommend that you do not perform DDL operations to change the schemas of source databases or tables. Otherwise, data inconsistency may occur or the data migration task fails.
Source Objects	Select one or more objects from the Source Objects section. Click the icon and 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 as the objects to be migrated, DTS does not migrate other objects such as views, triggers, or stored procedures to the destination database. If you select a database as the object to be migrated, DTS migrates data based on the following default rules: If the table to be migrated in the source database has a primary key, such as a single-column primary key or a composite primary key, the primary key columns are specified as the distribution keys. If the table to be migrated in the source database does not have a primary key, an auto-increment primary key column is automatically generated in the destination table. This may cause data inconsistency between the source and destination databases.
Selected Objects	To rename an object that you want to migrate to the destination instance, right-click the object in the Selected Objects section. For more information, see Map the name of a single object. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time. Note If you use the object name mapping feature to rename an object, other objects that are dependent on the object may fail to be migrated. To specify WHERE conditions to filter data, right-click an object in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Use SQL conditions to filter data. To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to migrate. For more information about the SQL operations that can be migrated, see SQL operations that can be migrated.

Click Next: Advanced Settings to configure advanced settings.


Parameter	Description
Set Alerts	Specifies whether to set alerts for the data migration task. If the task fails or the migration latency exceeds the threshold, the alert contacts will receive notifications. Valid values: No: does not set alerts. Yes: sets alerts. If you select Yes, you must also set the alert threshold and alert contacts.
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 ensure that the capitalization of object names is consistent with that in the source or destination database. For more information,see Specify the capitalization of object names in the destination instance.
Replicate Temporary Tables When DMS Performs DDL Operations	If you use DMS to perform online DDL operations on the source database, you can specify whether to migrate temporary tables generated by online DDL operations. Valid values: Yes: DTS migrates the data of temporary tables generated by online DDL operations. Note If online DDL operations generate a large amount of data, the data migration task may take an extended period of time to complete. No: DTS does not migrate the data of temporary tables generated by online DDL operations. Only the original DDL data of the source database is migrated. Note If you select No, the tables in the destination database may be locked.
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 time range. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the parameter to a value greater than 30. If DTS reconnects 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 set different retry time ranges for multiple data migration tasks that have the same source or destination database, the shortest retry time range that is set 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 your earliest opportunity after the source and destination instances are released.
Configure ETL	Specify whether to configure the extract, transform, and load (ETL) feature. For more information, see What is ETL?. 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.
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, latency of the DTS instance may be displayed. No: writes SQL operations on heartbeat tables. In this case, features such as physical backup and cloning of the source database may be affected.

Specify the primary key columns and distribution key columns of the tables that you want to migrate to the AnalyticDB for MySQL cluster.
Note
- If you select Schema Migration as Task Stages, you must specify the Type, Primary Key Column, and Distribution Key parameters for the tables that you want to migrate to the AnalyticDB for MySQL V3.0 cluster. For more information, see CREATE TABLE.
- If you select Full Data Synchronization as Task Stages, the Primary Key Column and Distribution Key parameters are set based on the following rules by default:
  
  If the table to be migrated in the source database has a primary key, such as a single-column primary key or a composite primary key, the primary key columns are specified as the distribution keys.
  
  If the table to be migrated in the source database does not have a primary key, and you do not specify a primary key for the table in the destination database, an auto-increment primary key column is automatically generated. This may cause data inconsistency between the source and destination databases.
In the lower part of the page, click Next: Save Task Settings and Precheck.
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, you can click the icon next to each failed item to view details.
  
  You can troubleshoot the issues based on the causes and run a precheck again.
  
  If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.
Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.

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


Section	Parameter	Description
Parameters	Instance Class	DTS provides several instance classes that have different performance in migration speed. You can select an instance class based on your business scenario. For more information, see Specifications of data migration instances.

Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start to start the data migration task. You can view the progress of the task in the task list.