This topic describes how to synchronize data from an ApsaraDB RDS for MySQL instance to a self-managed MySQL database that is connected over Express Connect, VPN Gateway, or Smart Access Gateway by using Data Transmission Service (DTS) in real time.

Prerequisites

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%.
  • 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.

Billing

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

Limits

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.

  • We recommend that you do not use gh-ost or pt-online-schema-change to perform DDL operations on objects during data synchronization. Otherwise, data synchronization may fail.
  • 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.

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
  • Two-way one-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 synchronize 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 between the source and destination databases. For example, if only Table A is selected as the object to synchronize and 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 to synchronize when you configure the data synchronization task.

Procedure

  1. Purchase a data synchronization instance. For more information, see Purchase a DTS instance.
    Note Select MySQL for both the source instance and the destination instance. Select One-Way Synchronization as the synchronization topology.
  2. Log on to the DTS console.
  3. In the left-side navigation pane, click Data Synchronization.
  4. In the upper part of the Synchronization Tasks page, select the region where the data synchronization instance resides.
  5. Find the data synchronization instance and click Configure Task in the Actions column.
  6. Configure the source and destination instances.
    Section Parameter Description
    N/A Synchronization 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 Instance Details Instance Type Select RDS Instance.
    Instance Region The source region that you selected on the buy page. The value of this parameter cannot be changed.
    Instance ID Select the ID of the source RDS instance.
    Database Account Enter the database account of the source RDS instance.
    Note If the database type of the source RDS instance is MySQL 5.5 or MySQL 5.6, you do not need to configure the database account or database password.
    Database Password Enter the password of the database account.
    Encryption Select Non-encrypted or SSL-encrypted. If you want to select SSL-encrypted, you must enable SSL encryption for the RDS instance before you configure the data synchronization task. For more information, see Configure SSL encryption for an ApsaraDB RDS for MySQL instance.
    Notice The Encryption parameter is available only for regions in the Chinese mainland and the China (Hong Kong) region.
    Destination Instance Details Instance Type Select User-Created Database Connected over Express Connect, VPN Gateway, or Smart Access Gateway.
    Instance Region The destination region that you selected on the buy page. The value of this parameter cannot be changed.
    Peer VPC Select the ID of the VPC that is connected to the self-managed database.
    Database Type Set the value to MySQL. The value of this parameter cannot be changed.
    IP Address Enter the server IP address of the self-managed MySQL database.
    Port Number Enter the service port number of the self-managed MySQL database. The default port number is 3306.
    Database Account Enter the account of the self-managed MySQL database.
    Note The account must have the SELECT permission on the objects to be synchronized, the REPLICATION CLIENT permission, the REPLICATION SLAVE permission, and the SHOW VIEW permission.
    Database Password Enter the password of the database account.
  7. In the lower-right corner of the page, click Set Whitelist and Next.
    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.
  8. Select the synchronization policy and the objects to synchronize.
    Select objects for a one-way data synchronization task
    Setting Description
    Select the objects to be synchronized

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

    You can select tables or databases as the objects to synchronize.

    Note
    • If you select a database as the object to synchronize, all schema changes in the database are synchronized to the destination database.
    • By default, after an object is synchronized to the destination database, the name of the object remains unchanged. You can use the object name mapping feature to rename the objects that are synchronized to the destination instance. For more information, see Rename an object to be synchronized.
    Rename Databases and Tables

    You can use the object name mapping feature to rename the objects that are synchronized to the destination instance. For more information, see Object name mapping.

    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 Connections
    By default, if DTS fails to connect to the source or destination database, DTS retries within the next 720 minutes (12 hours). You can specify the retry time based on your needs. 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 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.
  9. In the lower-right corner of the page, click Next.
  10. Select the initial synchronization types.
    Advanced Settings
    Note
    • During initial synchronization, DTS synchronizes the schemas and data of required objects from the source instance to the destination instance. The schemas and data are the basis for subsequent incremental synchronization.
    • Initial synchronization includes initial schema synchronization and initial full data synchronization. In most cases, you need to select both Initial Schema Synchronization and Initial Full Data Synchronization.
  11. In the lower-right corner of the page, click Precheck.
    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.
  12. Close the Precheck dialog box after the following message is displayed: Precheck Passed. Then, the data synchronization task starts.
  13. Wait until initial synchronization is complete and the data synchronization task enters the Synchronizing state.

    You can view the state of the data synchronization task on the Synchronization Tasks page.

    State of the data synchronization task