This topic describes how to synchronize data between ApsaraDB RDS for MySQL instances that belong to different Alibaba Cloud accounts by using Data Transmission Service (DTS).

Prerequisites

  • The source and destination ApsaraDB RDS for MySQL instances are created. For more information, see Create an ApsaraDB RDS for MySQL instance.
  • The database type of the source and destination ApsaraDB RDS instances is MySQL.

Precautions

  • DTS uses read and write resources of the source and destination databases during initial full data synchronization. This may increase the loads of the database servers. If the database performance is unfavorable, the specification is low, or the data volume is large, database services may become unavailable. For example, DTS occupies a large amount of read and write resources in the following cases: a large number of slow SQL queries are performed on the source database, the tables have no primary keys, or a deadlock occurs in the destination database. 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. For example, you can synchronize data when the CPU utilization of the source and destination databases is less than 30%.
  • The tables to be migrated in the source database must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records.
  • During initial full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination instance. After initial full data synchronization is complete, the size of used tablespace of the destination instance is larger than that of the source instance.

Supported synchronization topologies

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

For more information about synchronization topologies, see Synchronization topologies.

SQL operations that can be synchronized

Operation type SQL statement
DML INSERT, UPDATE, DELETE, and REPLACE
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

Limits

  • Incompatibility with triggers

    If you select a database as the object to be synchronized and the database contains a trigger that updates a table, data inconsistency may occur. For more information about how to solve this issue, see Configure a data synchronization task for a source database that contains a trigger.

  • Limits on RENAME TABLE operations

    RENAME TABLE operations may cause data inconsistency during synchronization. For example, if only Table A needs to be synchronized and it is renamed Table B, Table B cannot be synchronized to the destination database. To prevent this situation, you can select the entire database where Table A is located as the object when you configure the data synchronization task.

Preparations

Set the Alibaba Cloud account that owns the destination ApsaraDB RDS for MySQL instance as a trusted account. This allows DTS to access the cloud resources of the Alibaba Cloud account that owns the source ApsaraDB RDS for MySQL instance. For more information, see Configure RAM authorization for cross-account data migration and synchronization.

Note To authorize the Alibaba Cloud account that owns the destination instance, you must log on to the Resource Access Management (RAM) console with the Alibaba Cloud account that owns the source instance. Then, you can create a data migration task or data synchronization task by using the Alibaba Cloud account that owns the destination instance.

Procedure

  1. Go to the Data Synchronization page of the new DTS console.
    Note You can also log on to the Data Management (DMS) console. In the top navigation bar, choose DTS > Data Synchronization.
  2. In the upper-left corner of the page, select the region where the data synchronization instance resides.
    Select a 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 at the top of the page. This helps you create and run the data synchronization 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 Select Instance
    You have the option to select an existing instance based on your 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 configure the following parameters.
    Database Type Select MySQL.
    Access Method Select Cloud Instance.
    Instance Region The region where the source ApsaraDB RDS for MySQL instance resides.
    Note You can select different regions for the source and destination ApsaraDB RDS for MySQL instances.
    Replicate Data Across Alibaba Cloud Accounts Select Yes.
    Alibaba Cloud Account The Alibaba Cloud account that owns the source ApsaraDB RDS for MySQL instance.
    Note To obtain the ID of the Alibaba Cloud account that owns the source instance, you must log on to the Account Management console by using this account. The account ID is displayed on the Security Settings page.
    RAM Role Name The role name configured for the Alibaba Cloud account that owns the source instance. For more information, see Configure RAM authorization for cross-account data migration and synchronization.
    RDS Instance ID The ID of the source ApsaraDB RDS for MySQL instance.
    Note If an alert message appears when you select an ApsaraDB RDS instance ID, modify the parameter values as prompted. For more information, see the "FAQ" section of this topic.
    Database Account The database account of the source ApsaraDB RDS for MySQL instance.
    Database Password

    Enter the password of the database account.

    Encryption Select Non-encrypted or SSL-encrypted based on your requirements. In this example, Non-encrypted is selected.
    Note If you want to select SSL-encrypted, you must enable SSL encryption for the ApsaraDB RDS for MySQL instance before you configure the data synchronization task. For more information, see Configure SSL encryption for an ApsaraDB RDS for MySQL instance.
    Destination Database Select Instance
    You have the option to select an existing instance based on your 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 configure the following parameters.
    Database Type Select MySQL.
    Access Method Select Cloud Instance.
    Instance Region The region where the destination ApsaraDB RDS for MySQL instance resides.
    Note You can select different regions for the source and destination RDS instances.
    RDS Instance ID The instance ID of the destination ApsaraDB RDS for MySQL instance.
    Database Account The database account of the destination database.
    Database Password

    Enter the password of the database account.

    Encryption Select Non-encrypted or SSL-encrypted based on your requirements. In this example, Non-encrypted is selected.
    Note If you want to select SSL-encrypted, you must enable SSL encryption for the ApsaraDB RDS instance before you configure the data migration task. For more information, see Configure SSL encryption for an ApsaraDB RDS for MySQL instance.
  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 Elastic Compute Service (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 objects for the task and configure advanced settings.
    • Basic SettingsBasic Settings
      Setting Description
      Task Stages

      Incremental Data Synchronization is selected by default. You must also select Schema Synchronization and Full Data Synchronization. After the precheck, DTS synchronizes the historical data of the 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 precheck and the data synchronization task cannot be started.

        Note You can use the object name mapping feature to rename the tables that are synchronized 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 consistency is not guaranteed 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, data may fail to be initialized. In this case, only some 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 move the objects to the Selected Objects section.

      Note You can select columns, tables, or databases as the objects to be synchronized.
      Rename Databases and Tables
      • To rename an object that you want to synchronize 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.
      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 and DDL operations that you want to synchronize. For more information, see SQL operations that can be synchronized.
    • Advanced SettingsAdvanced Settings
      Parameter Description
      Set Alerts
      Specify whether to set alerts for the data synchronization task. If the task fails or the synchronization 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 synchronize temporary tables generated by online DDL 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, the data synchronization task may be delayed.
      • 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
      Specify the retry time for failed connections. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the retry time to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified time, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails.
      Note
      • If multiple DTS instances have the same source or destination database, the lowest value takes effect. For example, the retry time is set to 30 minutes for Instance A and 60 minutes for Instance B, DTS retries failed connections at an interval of 30 minutes.
      • When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time 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.
      • 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.
  7. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.
  8. On the Purchase Instance page, specify the Billing Method and Instance Class parameters for the data synchronization instance. The following table describes the parameters.
    Section Parameter Description
    Parameters Billing Method
    • Subscription: You can pay for your subscription when you create an instance. We recommend that you select the subscription billing method for long-term use because it is more cost-effective than the pay-as-you-go billing method. You can save more costs with longer subscription periods.
    • Pay-as-you-go: A pay-as-you-go instance is billed on an hourly basis. We recommend that you select the pay-as-you-go billing method for short-term use. If you no longer require your pay-as-you-go instance, you can release it 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 Length If you select the subscription billing method, set the subscription length and the number of instances that you want to create. The subscription length 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.

FAQ

The following table describes the common alert messages and the corresponding solutions when you configure the source database.

Alert message Solution
UID Check whether you specify a valid value for the Cloud Account or RAM Role Name parameter when you configure the source instance.
Note To obtain the ID of the Alibaba Cloud account that owns the source instance, you can log on to the Account Management console by using this account. The account ID is displayed on the Security Settings page.
ROLE