This topic describes how to migrate incremental data from a self-managed TiDB database to an ApsaraDB RDS for MySQL instance by using Data Transmission Service (DTS). Incremental data migration allows you to ensure service continuity when you migrate data to Alibaba Cloud. In this example, Pump, Drainer, and a Kafka cluster are deployed.
Prerequisites
- The destination ApsaraDB RDS for MySQL instance must reside in the China (Hangzhou), China (Shanghai), China (Qingdao), China (Beijing), China (Shenzhen), China (Zhangjiakou), China (Hong Kong), Singapore (Singapore), US (Silicon Valley), or US (Virginia) region.
- The available storage space of the destination ApsaraDB RDS for MySQL instance must be larger than the total size of the data in the self-managed TiDB database.
Background information

The binary log format and implementation mechanism of a TiDB database are different from those of a MySQL database. To migrate incremental data and minimize modifications to the source TiDB database, you must deploy Pump, Drainer, and a Kafka cluster.
Pump records the binary log files that are generated in TiDB in real time, and sends the binary log files to Drainer. Drainer writes the binary log files to the downstream Kafka cluster. During incremental data migration, DTS retrieves data from the Kafka cluster and migrates the data to the destination database in real time. For example, DTS can migrate incremental data to an ApsaraDB RDS for MySQL instance.
Precautions
- DTS uses read and write resources of the source and destination databases during full data migration. 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 migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. For example, you can migrate 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.
- DTS uses the
ROUND(COLUMN,PRECISION)
function to retrieve values from columns of the FLOAT or DOUBLE data type. If you do not specify a precision, DTS sets the precision for the FLOAT data type to 38 digits and the precision for the DOUBLE data type to 308 digits. You must check whether the precision settings meet your business requirements. - DTS automatically creates a destination database in the ApsaraDB RDS for MySQL instance.
However, if the name of the source database is invalid, you must manually create a
database in the ApsaraDB RDS for MySQL instance before you configure the data migration
task.
Note For more information about the naming conventions of ApsaraDB RDS for MySQL databases and how to create a database, see Create a database on an ApsaraDB RDS for MySQL instance.
- If a data migration task fails, DTS automatically resumes the task. Before you switch your workloads to the destination instance, stop or release the data migration task. Otherwise, the data in the source database will overwrite the data in the destination instance after the task is resumed.
Billing
Migration type | Task configuration fee | Internet traffic fee |
---|---|---|
Schema migration and full data migration | Free of charge. | Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Pricing. |
Incremental data migration | Charged. For more information, see Pricing. |
Migration types
Migration type | Description |
---|---|
Schema migration | DTS migrates the schemas of required objects to the destination database. DTS supports
schema migration for views, tables, and databases.
Warning TiDB and MySQL are heterogeneous databases. DTS does not ensure that the schemas of
the source and destination databases are consistent after schema migration. We recommend
that you evaluate the impact of data type conversion on your business. For more information,
see Data type mappings between heterogeneous databases.
|
Full data migration | DTS migrates the historical data of required objects to the destination database.
Note During full data migration, concurrent INSERT operations cause fragmentation in the
tables of the destination database. After full data migration is complete, the size
of used tablespace of the destination database is larger than that of the source database.
|
Incremental data migration | DTS retrieves binary log files that are generated in TiDB from the Kafka cluster,
and migrates incremental data to the destination database in real time. During incremental
data migration, the following SQL operations can be synchronized:
Incremental data migration allows you to ensure service continuity when you migrate data from a self-managed TiDB database to Alibaba Cloud. |