This topic describes how to synchronize data from an ApsaraDB RDS for MySQL instance to a PolarDB-X V2.0 instance by using Data Transmission Service (DTS).

Supported source databases

You can use DTS to synchronize data from the following types of MySQL databases to a PolarDB-X V2.0 instance. In this topic, an ApsaraDB RDS for MySQL instance is used to describe how to configure a data synchronization task. You can also follow the procedure to configure data synchronization tasks for other types of MySQL databases.
  • ApsaraDB RDS for MySQL instance
  • Self-managed database that is hosted on Elastic Compute Service (ECS)
  • Self-managed database that is connected over Express Connect, VPN Gateway, or Smart Access Gateway
  • Self-managed database that is connected over Database Gateway
  • Self-managed database that is connected over Cloud Enterprise Network (CEN)

Prerequisites

  • A PolarDB-X V2.0 instance is created and its storage type is MySQL 5.x.
  • The available storage space of the PolarDB-X V2.0 instance is larger than the total size of the data in the ApsaraDB RDS for MySQL instance.

Limits

Note By default, DTS disables FOREIGN KEY constraints for the destination database in a data synchronization task. Therefore, the cascade and delete operations of the source database are not synchronized to the destination database.
Category Description
Limits on the source database
  • The tables to synchronize 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 synchronize and you want to edit tables (such as renaming tables or columns) in the destination database, up to 1,000 tables can be synchronized 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 split the tables and configure multiple tasks to synchronize the tables, or configure a task to synchronize the entire database.
  • The following requirements for binary logs must be met:
    • The binary logging feature is 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.
      Notice
      • 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. After full data synchronization is complete, 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 exceptional circumstances, data inconsistency or loss may occur. Make sure that you set the retention period of binary logs in accordance with the preceding requirements. Otherwise, the Service Level Agreement (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.

Precautions
  • Schema synchronization is not supported in this scenario. Before you configure a data synchronization task, you must create databases and tables in the destination instance.
  • Requirements for the objects to synchronize:
    • DTS does not synchronize the following data types: BIT, VARBIT, GEOMETRY, ARRAY, UUID, TSQUERY, TSVECTOR, and TXID_SNAPSHOT.
    • 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 size of the used 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 Change schemas without locking tables.

  • 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. 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 synchronization latency 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 synchronize, you can create a heartbeat table. The heartbeat table is updated or receives data every second.

Billing

Synchronization type Task configuration fee
Schema synchronization and full data synchronization Free of charge.
Incremental data synchronization Charged. For more information, see Pricing.

Supported synchronization topologies

  • One-way one-to-one synchronization
  • One-way many-to-one synchronization

SQL operations that can be synchronized

Operation type SQL statement
DML INSERT, UPDATE, and DELETE
DDL
  • ALTER TABLE and ALTER VIEW
  • CREATE FUNCTION, CREATE INDEX, CREATE PROCEDURE, CREATE TABLE, and CREATE VIEW
  • DROP INDEX and DROP TABLE
  • RENAME TABLE
  • TRUNCATE TABLE

Procedure

  1. Go to the Data Synchronization page of the new DTS console.
    Note You can also log on to the Data Management console. In the top navigation bar, click DTS. Then, in the left-side navigation pane, choose DTS (DTS) > Data Synchronization.
  2. In the upper-left corner of the page, select the region where the data synchronization instance resides.
    Region
  3. 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 in the upper part of the page. This ensures that you create and run the data synchronization task.
    Configure the source and destination databases
    Section Parameter Description
    N/A Task Name

    The task name that DTS automatically generates. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to use a unique task name.

    Source Database Database Type Select MySQL.
    Access Method Select Cloud Instance.
    Instance Region The region where the source ApsaraDB RDS for MySQL instance resides.
    Replicate Data Across Alibaba Cloud Accounts Specifies whether data is synchronized across Alibaba Cloud accounts. In this example, No is selected.
    RDS Instance ID The ID of the source ApsaraDB RDS for MySQL instance.
    Database Account The database account of the source ApsaraDB RDS for MySQL instance. The account must have the REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions.
    Database Password

    The password of the database account.

    Encryption

    Select Non-encrypted or SSL-encrypted based on your requirements. If you want to select SSL-encrypted, you must enable SSL encryption for the source 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 PolarDB-X 2.0.
    Access Method Select Cloud Instance.
    Instance Region The region where the destination PolarDB-X V2.0 instance resides.
    Instance ID The ID of the destination PolarDB-X V2.0 cluster.
    Database Account The database account of the destination PolarDB-X V2.0 instance. The account must have read and write permissions.
    Database Password

    The password of the database account.

  4. In the lower part of the page, click Test Connectivity and Proceed.
    Note
    • You do not need to modify the security settings for ApsaraDB instances (such as ApsaraDB RDS for MySQL and ApsaraDB for MongoDB) and ECS-hosted databases. DTS automatically adds the CIDR blocks of DTS servers to the whitelists of ApsaraDB instances or the security group rules of ECS instances. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.
    • After data synchronization is complete, we recommend that you remove the CIDR blocks of DTS servers from the whitelists or security groups.
  5. Select the objects to migrate.
    • Basic SettingsBasic Settings
      Parameter Description
      Task Stages

      By default, Incremental Data Synchronization is selected. You can select only Full Data Synchronization. Schema Synchronization cannot be selected. After the precheck is complete, DTS synchronizes the historical data of selected objects from the source instance to the destination cluster. The historical data is the basis for subsequent incremental synchronization.

      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 the precheck and the data synchronization 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, and a data record has the same primary key as an existing data record in the destination database:
          • During full data synchronization, DTS does not synchronize the data record to the destination database. The existing data record in the destination database is retained.
          • During incremental data synchronization, DTS synchronizes the data record to the destination database. The existing data record in the destination database is overwritten.
        • If the source and destination databases have different schemas, initial data synchronization may fail. In this case, only part of the columns are synchronized, or the data synchronization task fails.
      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 databases as objects to synchronize. If you select tables or columns as the objects to synchronize, DTS does not synchronize other objects such as views, triggers, and stored procedures to the destination database.
      Rename Databases and Tables
      • To rename an object in 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 in the destination instance, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time.
      Filter data

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

      Select the SQL operations to be synchronized In the Selected Objects section, right-click an object. In the dialog box that appears, select the DML operations that you want to synchronize. For more information, see SQL operations that can be synchronized.
    • Advanced SettingsAdvanced Settings
      Parameter Description
      Set Alerts
      Specifies whether to set alerts for the data synchronization task. If you select yes, DTS sends notifications to contacts if the task fails or the synchronization latency exceeds the upper limit.
      • No: does not set alerts.
      • Yes: sets alerts. In this case, you must also set the alert threshold and alert contacts.
      Capitalization of Object Names in Destination Instance

      Specifies 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
      In this scenario, DTS cannot synchronize DDL operations. You must set this parameter to No. However, DTS may support DDL operations for this scenario in the future. In this case, if you use DMS to perform online DDL operations on the source database, you can specify whether to synchronize temporary tables generated by the operations.
      • Yes: DTS synchronizes the data of temporary tables generated by online DDL operations.
        Note If online DDL operations generate a large amount of data, latency may occur in the data synchronization task.
      • No: DTS does not synchronize the data of temporary tables generated by online DDL operations. Only the original DDL data of the source database is synchronized.
        Note If you select No, the tables in the destination database may be locked.
      Retry Time for Failed Connection
      Specifies the retry time range for failed connections. Valid values: 10 to 1440. Unit: minutes. Default value: 120. 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 less value that is specified for the instance 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.
  6. Click Next: Save Task Settings and Precheck in the lower part of the page.
    Note
    • Before you can start the data synchronization task, DTS performs a precheck. You can start the data synchronization 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.
      • After you troubleshoot the issues based on the causes, you can run a precheck again.
      • If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.
  7. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.
  8. On the Purchase Instance page, specify the billing method and specifications for the data synchronization instance. The following table describes related parameters.
    Section Parameter Description
    Parameters Billing method
    • Subscription: You pay for your subscription when you create an instance. The subscription billing method is more cost-effective than the pay-as-you-go billing method for long-term use.
    • Pay-as-you-go: A pay-as-you-go instance is billed on an hourly basis. For short-term use, we recommend that you select the pay-as-you-go billing method. If you no longer need a pay-as-you-go instance, you can release the instance to reduce costs.
    Instance Class DTS provides several instance classes that have different performance in synchronization speed. You can select an instance class based on your business scenario. For more information, see Specifications of data synchronization instances.
    Subscription Duration If you select the subscription billing method, set the subscription duration and the number of instances that you want to create. The subscription duration can be one to nine months or one to three years.
    Note This parameter is available only if you select the subscription billing method.
  9. Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
  10. Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.