This topic describes how to migrate data from an ApsaraDB RDS for MySQL instance to an AnalyticDB for PostgreSQL instance by using Data Transmission Service (DTS).

Supported source databases

You can migrate data from the following types of MySQL databases to an AnalyticDB for PostgreSQL instance:
  • ApsaraDB RDS for MySQL instance
  • Self-managed MySQL databases:
    • Self-managed database with a public IP address
    • Self-managed database that is hosted on an Elastic Compute Service (ECS) instance
    • Self-managed database that is connected over Database Gateway
    • Self-managed database that is connected over Cloud Enterprise Network (CEN)
    • Self-managed database that is connected over Express Connect, VPN Gateway, or Smart Access Gateway
Note In this topic, an ApsaraDB RDS for MySQL instance is used to describe how to configure a data migration task. You can also follow the procedure to configure data migration tasks for other types of MySQL databases.

Prerequisites

Limits

Category Description
Limits on the source database
  • The tables to be synchronized 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 synchronized and you need to edit the tables, such as renaming tables or columns, in the destination database, you can synchronize up to 1,000 tables in a single data synchronization task. If you run a task to synchronize more than 1,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to synchronize the tables in batches or configure a task to synchronize the entire database.
  • The following requirements for binary logs must be met:
    • The binary logging feature must be enabled. For more information about how to enable binary logging, see Modify the parameters of an ApsaraDB RDS for MySQL instance. In addition, the binlog_row_image parameter must be set to full. Otherwise, error messages are returned during precheck and the data synchronization task cannot be started.
      Important
      • If the source database is a self-managed MySQL database, you must enable binary logging and set binlog_format to row and binlog_row_image to full.
      • If the self-managed MySQL database is deployed in a dual-primary cluster, you must set log_slave_updates to ON. This ensures that DTS can obtain all binary logs. For more information, see Create an account for a user-created MySQL database and configure binary logging.
    • For an incremental data synchronization task, the binary logs of the source database are retained for at least 24 hours. For a full data and incremental data synchronization task, the binary logs of the source database are retained for at least seven days. Otherwise, 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 synchronization 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 SLA of DTS does not ensure service reliability and performance. For more information about binary log files and log backup files of an ApsaraDB RDS for MySQL instance, see View and delete the binary log files of an ApsaraDB RDS for MySQL instance.

  • During data synchronization, do not perform DDL operations to modify the primary key or add comments because the operations cannot take effect. For example, do not execute the ALTER TABLE table_name COMMENT='Table comments'; statement.
Other limits
  • Requirements for the objects to be synchronized:
    • Only tables can be selected as the objects to be synchronized.
    • DTS does not synchronize the following data types: BIT, VARBIT, GEOMETRY, ARRAY, UUID, TSQUERY, TSVECTOR, TXID_SNAPSHOT, and POINT.
    • Prefix indexes cannot be synchronized. If the source database contains prefix indexes, data may fail to be synchronized.
  • Before you synchronize data, evaluate the impact of data synchronization on the performance of the source and destination databases. We recommend that you synchronize data during off-peak hours. During full data synchronization, DTS uses read and write resources of the source and destination databases. This may increase the loads on the database servers.
  • During full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data synchronization is complete, the tablespace of the destination database is larger than that of the source database.
  • If you select one or more tables instead of an entire database as the objects to synchronize, do not use gh-ost or pt-online-schema-change to perform DDL operations on the tables during data synchronization. Otherwise, data may fail to be synchronized.

    If you use only DTS to write data to the destination database, you can use Data Management (DMS) to perform online DDL operations on source tables during data synchronization. For more information, see Perform lock-free DDL operations.

  • During data synchronization, we recommend that you use only DTS to write data to the destination database. This prevents data inconsistency between the source and destination databases. For example, if you use tools other than DTS to write data to the destination database, data loss may occur in the destination database when you use DMS to perform online DDL operations.
Special cases
If the source database is a self-managed MySQL database, take note of the following items:
  • If you perform a primary/secondary switchover on the source database when the data synchronization task is running, the task fails.
  • DTS calculates synchronization latency based on the timestamp of the latest synchronized data in the destination database and the current timestamp in the source database. If no DML operation is performed on the source database for a long time, the synchronization latency may be inaccurate. If the latency of the synchronization task is too high, you can perform a DML operation on the source database to update the latency.
    Note If you select an entire database as the object to be synchronized, you can create a heartbeat table. The heartbeat table is updated or receives data every second.
  • 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 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 Billing overview.
Incremental data migration Charged. For more information, see Billing overview.

Migration types

  • Schema migration

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

    Note In this topic, the source and destination databases 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 required objects from the source database to the destination database.

  • Incremental data migration

    After full data migration is complete, DTS migrates incremental data from the source database to the destination database. Incremental data migration ensures 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 occurs and the data migration task is stopped. You can perform the following steps to troubleshoot the issue:
  1. 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 PostgreSQL instance.
  2. Create a table named customer_new in the destination AnalyticDB for PostgreSQL instance. The customer_new table has the same schema as the customer table.
  3. 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.
  4. Rename or delete the customer table. Then, change the name of the customer_new table to customer.
  5. Restart the data migration task in the DTS console.

Permissions required for database accounts

Instance type Schema migration Full data migration Incremental data migration
ApsaraDB RDS for MySQL The SELECT permission The SELECT permission The SELECT permission on the objects to be migrated, the REPLICATION SLAVE permission, and the REPLICATION CLIENT permission. DTS automatically grants these permissions to the database account.
AnalyticDB for PostgreSQL Read and write permissions
For more information about how to create and authorize a database account, see the following topics:

Procedure

  1. Go to the Data Migration page.
    1. Log on to the DMS console.
    2. In the top navigation bar, click DTS. In the left-side navigation pane, choose DTS (DTS) > Data Synchronization.
  2. From the drop-down list next to 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.
  3. Click Create Task. On the page that appears, configure the source and destination databases.
    Section Parameter Description
    N/A Task Name

    DTS automatically generates a task name. We recommend that you specify an informative name to identify the task. You do not need to use a unique task name.

    Source Database Database Type Select MySQL.
    Access Method Select Alibaba Cloud Instance.
    Instance Region The region in which the source ApsaraDB RDS for MySQL instance resides.
    Replicate Data Across Alibaba Cloud Accounts Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
    RDS Instance ID Select the ID of the source ApsaraDB RDS for MySQL instance.
    Database Account The database account of the source ApsaraDB RDS for MySQL instance. 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.

    Encryption

    Select Non-encrypted or SSL-encrypted based on your business requirements. If you want to select SSL-encrypted, you must enable SSL encryption for the ApsaraDB RDS for MySQL instance before you configure the data migration task. For more information, see Configure SSL encryption for an ApsaraDB RDS for MySQL instance.

    Destination Database Database Type Select AnalyticDB for PostgreSQL.
    Access Method Select Alibaba Cloud Instance.
    Instance Region The region in which the destination AnalyticDB for PostgreSQL instance resides.
    Instance ID The ID of the destination AnalyticDB for PostgreSQL instance.
    Database Name The name of the destination database in the AnalyticDB for PostgreSQL instance.
    Database Account The initial account of the destination AnalyticDB for PostgreSQL instance.
    Note You can also enter an account that has the RDS_SUPERUSER permission. For more information, see Manage users and permissions.
    Database Password

    Enter the password of the database account.

  4. 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.
  5. Select objects for the task and configure advanced settings.
    • Basic Settings
      Parameter or setting 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 tables that have the same names, the precheck is passed. Otherwise, an error is returned during precheck and the data migration task cannot be started.

        Note If the source and destination databases contain tables that have the same 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 .
      • Clear Destination Table: skips the precheck for empty destination tables and clears the data in destination tables before the full data migration task is initialized.

      • 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 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.
      Select Objects

      Select one or more objects from the Source Objects section and click the Rightwards arrow icon to add the objects to the Selected Objects section.

      Note You can select columns, tables, or schemas 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, and stored procedures to the destination database.
      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 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.
      Filter the data to be migrated

      You can specify WHERE conditions to filter data. For more information, see Use SQL conditions to filter data.

      Select SQL operations for incremental data synchronization 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
      Parameter or setting 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.
      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 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 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 requirements. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
      Enclose Object Names in Quotation Marks Specify whether to enclose object names in quotation marks.
      • If you select Yes, DTS automatically encloses the names of schemas, tables, and columns that meet specific requirements in single quotation marks (') or double quotation marks (") during schema migration and incremental data migration in the following scenarios
        • The business environment of the source database is case-sensitive but the database name contains both uppercase and lowercase letters.
        • A source table name does not start with a letter and contains characters other than letters, digits, and special characters.
          Note A source table name can contain only the following special characters: underscores (_), number signs (#), and dollar signs ($).
        • The names of the schemas, tables, or columns that you want to migrate are keywords, reserved keywords, or invalid characters in the destination database.
      • If you select No, DTS does not enclose object names in quotation marks.
      Configure ETL Specify whether to configure the extract, transform, and load (ETL) feature. If you select Yes, you must enter domain-specific language (DSL) statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task.
  6. Optional:Configure fields in the tables that you want to migrate. Specify the primary keys and distribution keys of the tables that you want to migrate to the AnalyticDB for PostgreSQL instance. For more information, see CREATE TABLE.
    Note You can perform this operation only if you select Schema Migration in the previous step.
  7. 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 Info icon 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.
  8. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.
  9. 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.

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