This topic provides answers to some frequently asked questions (FAQ) about Data Transmission Service (DTS).

What types of databases does DTS support?

DTS supports data transmission between various data sources, such as relational database management systems (RDBMS), NoSQL databases, and online analytical processing (OLAP) databases. For more information, see Supported databases.

Note DTS also supports data migration and synchronization from databases that are provided by third-party cloud vendors to Alibaba Cloud. For more information, see Overview of data migration scenarios.

How do data migration, data synchronization, and data change tracking work?

For more information, see Architecture.

What are the differences between data migration and data synchronization?

Item Data migration Data synchronization
Scenarios The data migration feature is used to migrate data from on-premises databases, self-managed databases hosted on Elastic Compute Service (ECS), and databases on third-party cloud vendors to Alibaba Cloud.

You can release a data migration task immediately after it is complete.

The data synchronization feature is used to synchronize data between two data sources in real time. It is suitable for scenarios such as active geo-redundancy, disaster recovery, cross-border data synchronization, query load balancing, cloud BI systems, and real-time data warehousing.

After you create a data synchronization task, it continuously synchronizes data between the specified data sources to ensure data consistency.

Supported database services For more information, see Overview of data migration scenarios. For more information, see Overview of data synchronization scenarios.
Supported deployment environments of databases
  • Self-managed database with a public IP address
  • Self-managed database without a public IP address or port number (connected over Database Gateway)
  • Self-managed database connected over Cloud Enterprise Network (CEN)
  • Self-managed database hosted on ECS
  • Self-managed database connected over Express Connect, VPN Gateway, or Smart Access Gateway
  • Self-managed database hosted on ECS
  • Self-managed database connected over Express Connect, VPN Gateway, or Smart Access Gateway
  • Self-managed database without a public IP address or port number (connected over Database Gateway)
  • Self-managed database connected over CEN
Note The data synchronization feature ensures low network latency through data transmission over an internal network.
Features
  • You can enable object name mapping for columns, tables, and databases.
  • You can filter the data to be migrated.
  • You can select the types of SQL operations to be synchronized. For example, you can synchronize only INSERT operations.
  • You can read and migrate data across self-managed databases that are deployed in virtual private clouds (VPCs) owned by different Alibaba Cloud accounts.
  • You can enable object name mapping for columns, tables, and databases.
  • You can filter the data to be synchronized.
  • You can modify the objects to be synchronized.
  • You can configure two-way data synchronization between MySQL databases.
  • You can select the types of SQL operations to be synchronized. For example, you can synchronize only INSERT operations.
Billing methods Only the pay-as-you-go billing method is supported. The pay-as-you-go and subscription billing methods are supported.
Billing rules You are billed only when incremental data migration is in progress, including the period when incremental data migration is paused. You are not billed for schema migration and full data migration.
  • If you use the pay-as-you-go billing method, billing starts after the task is configured and started. You are also billed when the task is paused.
  • If you use the subscription billing method, the fee is deducted at the time of purchase based on the selected quantity and configurations.
Note For databases that are not supported by the data synchronization feature (such as databases on ApsaraDB for MongoDB instances), you can perform incremental data migration. Incremental data migration can ensure that data is synchronized between the source and destination database.

How is the synchronization latency measured?

The synchronization latency is the difference between the timestamp of the latest synchronized data in the destination database and the current timestamp. The latency is measured in milliseconds.

Note A normal latency is less than 1,000 milliseconds.

What can I do if DTS cannot connect to the source or destination database?

For more information, see Source database connectivity and Destination database connectivity.

What is the billing method of DTS?

For more information about, see Pricing.

What are the differences between data migration instances and data synchronization instances?

For more information, see Specifications of data migration instances and Specifications of data synchronization instances.

Can I downgrade the specifications of a data synchronization instance or data migration instance?

No, this feature is not supported now.

Why is the price of data synchronization higher than that of data migration?

Data synchronization comes with more advanced features. For example, you can modify the objects to be synchronized. You can configure two-way data synchronization between MySQL databases. In addition, the data synchronization feature ensures low network latency through data transmission over an internal network.

Can I migrate or synchronize data across Alibaba Cloud accounts?

How do I migrate or synchronize data from or to database instances that reside in regions not supported by DTS?

  • For a data migration task, you can apply for a public endpoint for a database instance, such as an ApsaraDB RDS for MySQL instance. This way, the database instance can be connected to as a self-managed database with a public IP address. Then, add the CIDR blocks of DTS servers that reside in a region supported by DTS, such as China (Hangzhou), to the whitelist of the database instance. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.
  • For a data synchronization task, you cannot synchronize data from or to database instances in regions that are not supported by DTS because database instances cannot be connected to as self-managed databases with public IP addresses during data synchronization.

Can I migrate, synchronize, or track the changes of data in read-only database instances?

Only full data migration and schema migration support read-only database instances, such as ApsaraDB for RDS instances and PolarDB clusters, as sources. Incremental data migration, data synchronization, and data change tracking do not support read-only database instances as sources. This is because incremental data migration, data synchronization, and data change tracking require the system to read incremental logs such as binary logs. However, the system does not generate transaction logs for read-only database instances.

Can I migrate data within a single database instance?

Yes, you can migrate data within a single database instance. For more information, see Migrate data between databases with different names.

Can I migrate or synchronize DML and DDL operations?

Yes, you can migrate or synchronize DML and DDL operations between relational databases. The supported DML operations are INSERT, UPDATE, and DELETE. The supported DDL operations are CREATE, DROP, ALTER, RENAME, and TRUNCATE.

Note The supported DML and DDL operations are different in different scenarios. For example, if you synchronize data from a MySQL database to an AnalyticDB for MySQL 2.0 database, only the following DDL operations are supported: CREATE TABLE, ALTER TABLE, and DROP TABLE. In addition, only the following DML operations are supported: INSERT, UPDATE, and DELETE. For more information about the scenarios and the supported DML and DDL operations, see Overview of data migration scenarios and Overview of data synchronization scenarios.

Can I migrate or synchronize database shards and table shards?

Yes, you can migrate or synchronize database shards and table shards. For example, you can migrate or synchronize database shards and table shards from a MySQL database or a PolarDB for MySQL cluster to an AnalyticDB for MySQL database. This allows you to merge multiple tables.

Can I migrate or synchronize data across time zones and character sets?

Yes, you can migrate or synchronize data across time zones and character sets.

Can I change the names of objects that are migrated or synchronized to the destination database?

Yes, you can change the names of columns, tables, and databases by using the object name mapping feature. For more information, see Object name mapping and Rename an object to be synchronized.

Can I filter fields or data?

Yes, you can filter fields or data in a table. For more information, see Filter the data to be migrated and Use SQL conditions to filter data.

Can I add or remove objects to be synchronized?

Yes, you can add or remove objects to be synchronized. For more information, see Add an object to a data synchronization task and Remove an object from a data synchronization task.

What will happen if I modify data in the destination database during data synchronization or migration? Will the modification take effect?

  • The data synchronization or migration task may fail. If you perform operations on the destination objects in the destination database during data synchronization or migration, exceptions may occur. For example, a primary key conflict may happen or data records are not updated. In this case, the data synchronization or migration task may fail. If you perform operations that do not interrupt data synchronization or migration, the task is not affected. For example, if you create a table in the destination database and write data to the table, the task is not affected because the table is not a destination object.
  • DTS reads the information about the source database and migrates or synchronizes full data, schema data, and incremental data to the destination database. Therefore, modifications of data in the destination may be overwritten by migrated or synchronized data.

Why is the size of data in the destination database smaller than that in the source database after data migration is complete?

If the data to be migrated is filtered or the source database has many table shards, the size of data in the destination database may be smaller than that in the source database after data migration is complete.

How do I view the performance of data migration or synchronization?

For more information, see View the connection status and performance of incremental data migration or View the connection status and performance of data synchronization.

How do I consume tracked data?