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

Which databases do DTS tasks support in data migration, data synchronization, and change tracking mode?

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 sources and targets.

Note DTS also supports data migration and synchronization between databases that are provided by third-party cloud vendors. For more information, see Data migration procedure list.

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

The data synchronization mode and the incremental data migration phase of the data migration mode offer seemingly similar functionality. They both perform continuous replications. However, they have different focuses.

The incremental data migration phase of the data migration mode is intended for minimized-downtime migrations. While DTS loads the existing data of the source database, updates are still being made to the source database. The incremental data migration is to ensure the updates occurring during this period are eventually applied to the target database.

The data synchronization mode is intended for continuous replications. It is usually used for data replication between databases in a distributed system, for example, for redundancy and high availability. Compared with the incremental data migration phase of data migration, the data synchronization mode delivers higher performance and lower lag.

How is the synchronization delay measured?

The synchronization delay is the difference between the timestamp of the latest synchronized data in the target database and the current timestamp in the source database. The unit is milliseconds.

How do I consume tracked data by using a task in change tracking mode?

You can use a Kafka client to consume tracked data. For more information, see Use a Kafka client to consume tracked data

How is DTS billed?

DTS provides two billing methods: subscription and pay-as-you-go. Change tracking and data synchronization instances support both billing methods. Data migration mode instances only support pay-as-you-go.

The subscription billing method allows you to pay for your subscription when creating an instance. Subscription lengths are monthly or yearly, and you can renew the subscription either manually or automatically. We recommend that you select subscription billing if you plan to use DTS for a period lasting a month or longer.

The pay-as-you-go billing method allows you to pay for your DTS instance based on the time your tasks are running. A pay-as-you-go instance is billed on an hourly basis, and you can release a pay-as-you-go instance at any time. We recommend that you select this billing method for short term use.

For more information about billing methods, see Billing methods. For details about how DTS is priced, see the Pricing page.

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

Data synchronization mode 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 mode ensures low network latency through data transmission over the internal network.

What are the differences in performance between different instance sizes?

The maximum performance of data migration and data synchronization tasks depends on the instance size.

For information about how different instance sizes perform in different scenarios, see Data migration mode test data and Data synchronization mode test data.

Can instance sizes be downgraded and upgraded?

You can upgrade the instance size of instances in data migration or data synchronization mode. You can upgrade an instance size by finding it in the instance list, and then clicking Upgrade in the Actions column. Instance sizes cannot be downgraded.

Can I migrate or synchronize data between Alibaba Cloud accounts?

Can I migrate data within a single instance?

Yes, you can migrate data within a single 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 AnalyticDB for MySQL 2.0, only the following DDL operations are supported: CREATE TABLE, ALTER TABLE, and DROP TABLE. Only the following DML operations are supported: INSERT, UPDATE, and DELETE.

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 and Apsara PolarDB for MySQL cluster to AnalyticDB for MySQL. 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 name of objects that are migrated or synchronized to the target database?

Yes, you can change the name of columns, tables, and databases by using the object name mapping feature. For more information, see Object name mapping.

Can I filter columns and rows?

Yes, you can filter columns and rows in a table. For more information, see Data filtering.

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.

How do I view the performance metrics of data migration and synchronization tasks?

You can view performance metrics of data migration and data synchronization tasks in the DTS console. For information about how to view the metrics, see View performance metrics of incremental data migration and Check the synchronization performance.