Migrate data from a PolarDB for MySQL cluster to an AnalyticDB for MySQL V3.0 cluster - Data Migration (New Console)| Alibaba Cloud Documentation Center

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 data, you can use AnalyticDB for MySQL to build internal business intelligence (BI) systems, interactive query systems, and real-time report systems.

Prerequisites

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	Bandwidth requirements: The server to which the source database belongs must have sufficient egress bandwidth. Otherwise, the data migration speed is affected. 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 rename tables or columns), 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 split the tables to be migrated, configure multiple tasks to migrate the tables, or configure a task to migrate the entire database. If you want to migrate incremental data, you must make sure that the following requirements are met: The binary logging feature must be enabled. The value of the binlog_format parameter must be set to row. Otherwise, error messages are returned during precheck and the data migration task cannot be started. If you perform only incremental data migration, the binary logs of the source database must be stored for more than 24 hours. If you perform both full data migration and incremental data migration, the binary logs of the source database must be stored for at least seven days. After full data migration is completed, you can set the retention period to more than 24 hours. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In extreme cases, data may be inconsistent or lost. 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 and performance. Limits on operations: 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, `ALTER TABLE table_name COMMENT='Table comment';`. 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 will be inconsistent 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.
Precautions	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 that you want 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 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 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 meets 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 instance, stop or release the data migration task. You can also run the `revoke` command to revoke the write permissions from the accounts that are used by DTS to access the destination instance. Otherwise, the data in the source database will overwrite the data in the destination instance after the task is resumed.

Billing


Migration type	Task 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 Pricing.
Incremental data migration	Charged. For more information, see Pricing.

Migration types

Schema migration
DTS migrates the schemas of the required 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 historical data of the required 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 allows you to ensure service continuity when you migrate data between self-managed databases.

SQL operations that can be migrated


Operation type	SQL statements
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 generated and the data migration task is stopped. You can submit a ticket or perform the following steps to troubleshoot the issue.

When DTS migrates data to the destination AnalyticDB for MySQL cluster, the data type of a field named customer in the source table is changed. As a result, the data migration task fails.
In the destination AnalyticDB for MySQL V3.0 cluster, create a table named customer_new. The customer_new table has the same schema as the customer table.
Run the INSERT INTO SELECT command 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 permissions
PolarDB for MySQL	The read permissions on the objects to be migrated
AnalyticDB for MySQL V3.0	The read and write permissions

For more information about how to create and authorize 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 page of the new DTS console.

Note You can also log on to the Data Management (DMS) console. In the top navigation bar, click DTS.
In the upper-left corner of the page, select the region in which the data migration instance resides.

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	DTS automatically generates a task name. We recommend that you specify a descriptive name that makes it easy to identify. You do not need to use a unique task name.
Source Database	Database Type	Select PolarDB for MySQL.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source PolarDB for MySQL cluster resides.
	PolarDB Cluster ID	Select the ID of the source PolarDB for MySQL cluster.
	Database Account	Enter 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	Enter the password of the database account.
Destination Database	Database Type	Select AnalyticDB for MySQL 3.0.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination AnalyticDB for MySQL V3.0 cluster resides.
	Instance ID	Select the ID of the destination AnalyticDB for MySQL V3.0 cluster.
	Database Account	Enter 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	Enter 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 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: enhance the security of your account and password, limit the ports that are exposed, authenticate API calls, regularly check the whitelist or ECS security group rules and forbid unauthorized CIDR blocks, or connect the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
- After the DTS task is completed or released, we recommend that you manually detect and remove the added CIDR blocks from the whitelist of the database instance or ECS security group rules.

Configure objects to migrate and advanced settings.

Basic Settings Basic Settings (Merge Tables + Select SQL Operations)


Parameter	Description
Task Stages	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 Incremental Data Migration is not selected, we recommend that you do not write data to the source instance during data migration. This ensures data consistency between the source and destination instances.
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 identical table names, the precheck is passed. Otherwise, an error is returned during 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 identical table 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 inconsistency may occur 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	Select the SQL operations that you want to migrate 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, perform the following steps: In the Selected Objects section, right-click an object. In the dialog box that appears, select the SQL operations that you want to migrate.
Merge Tables	If you select Yes, DTS adds the `__dts_data_source` column to each table to record data sources. No: the default value. Note If you set this parameter to Yes, all the selected source tables in the task are merged into the destination table. To merge only the data source columns of specific tables, you can create two data migration tasks. 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 migration task fails.
Select Objects	Select one or more objects from the Source Objects section and click the icon to add the objects to the Selected Objects section.
Rename Databases and Tables	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 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.
Filter data	You can specify WHERE conditions to filter data. For more information, see Use SQL conditions to filter data.
	In the Selected Objects section, right-click an object. In the dialog box that appears, select the SQL operations that you want to migrate. For more information, see SQL operations that can be migrated.

Advanced Settings Advanced Settings (Capitalization of Object Names in Destination Instance + Replicate Temporary Tables When DMS Performs DDL Operations + Next: Configure Database and Table Fields)

Advanced Settings (Capitalization of Object Names in Destination Instance + Replicate Temporary Tables When DMS Performs DDL Operations + Next: Configure Database and Table Fields)


Parameter	Description
Set Alerts	Specify 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. Select No if you do not want to set alerts. Select Yes to set alerts. In this case, you must also set the alert threshold and alert contacts.
Capitalization of Object Names in Destination Instance	Specify 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.
Replicate Temporary Tables When DMS Performs DDL Operations	If you use Data Management (DMS) to perform online DDL operations on the source database, you can specify whether to migrate temporary tables generated by online DDL operations. 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 migration task may be delayed. 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	Specify the retry time range for failed connections. Valid values: 10 to 720. Unit: minutes. Default value: 720. We recommend that you set the retry time range to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Note If an instance serves as the source or destination database of multiple data synchronization tasks, the value that is set 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 needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.

Specify the primary key columns and distribution keys of the tables that you want to migrate to the AnalyticDB for MySQL cluster.

Note If you select Schema Migration as the migration type, you must specify the type, primary key column, and distribution key for the tables that you want to migrate to the AnalyticDB for MySQL V3.0 cluster. For more information, see CREATE TABLE.
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, 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 various migration specifications. The migration speed varies based on the migration specifications that you select based on your business requirements. 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.