Data Transmission Service:Migrate data from an RDS for MySQL instance to a PolarDB for MySQL cluster

Source database requirements

• The server hosting the source database must have enough outbound bandwidth. Insufficient bandwidth reduces migration speed.

• Tables must have PRIMARY KEY or UNIQUE constraints with all unique fields. Tables without these constraints may result in duplicate records in the destination.

• If you select tables as migration objects and need to rename tables or columns in the destination database, a single task supports up to 1,000 tables. For more than 1,000 tables, split them across multiple tasks or migrate the entire database instead.

• Do not perform DDL operations on databases or tables during schema migration or full data migration. The task fails if schemas change mid-migration.

• If you run full data migration only (without incremental), do not write to the source database during migration. To guarantee data consistency, use schema migration, full data migration, and incremental data migration together.

If you include incremental data migration, the source database must also meet these requirements:

• Binary logging is enabled, with binlog_format set to row and binlog_row_image set to full. If these conditions are not met, precheck returns errors and the task cannot start.

  • Important: For self-managed MySQL in a dual-primary cluster, set log_slave_updates to ON so DTS can capture all binary logs.

• Binary log retention period: Insufficient log retention causes DTS to fail to obtain binary logs, which may result in task failure or data loss. Meeting these retention requirements is necessary to achieve the Service Level Agreement (SLA) guarantees.

  • Incremental migration only: retain logs for more than 24 hours.

  • Full + incremental migration: retain logs for at least 7 days. After full migration completes, you can reduce retention to more than 24 hours.

Destination database requirements

• DTS automatically creates the destination database in the PolarDB for MySQL cluster. If the source database name is invalid, create the database manually before configuring the task. See Database Management.

• Throttling is not supported for full data migration.

Other limitations

• Use the same engine version for the source and destination databases to ensure compatibility.

• Full data migration uses read and write resources on both the source and destination databases, which increases load. Schedule migration during off-peak hours.

• Full data migration with concurrent INSERT operations causes table fragmentation in the destination. After migration completes, the destination tablespace is larger than the source.

• DTS uses ROUND(COLUMN, PRECISION) to read FLOAT and DOUBLE columns. If you do not specify a precision, DTS uses 38 digits for FLOAT and 308 digits for DOUBLE. Verify that these precision settings meet your requirements.

• DTS retries failed tasks for up to 7 days. Before switching workloads to the destination, stop or release the migration task — or run REVOKE to remove write permissions from the DTS account. Otherwise, if the task resumes automatically, data from the source may overwrite data in the destination.

Self-managed MySQL sources only

• If a primary/secondary failover occurs while the migration task is running, the task fails.

• DTS calculates migration latency based on the timestamp of the latest migrated data in the destination and the current timestamp in the source. If no DML operations run on the source for an extended period, the reported latency may be inaccurate. Run a DML operation on the source to refresh the latency. If you migrate an entire database, create a heartbeat table that receives an update every second.

• DTS periodically runs CREATE DATABASE IF NOT EXISTS `test` on the source to advance the binary log file position.

Step 1: Go to the Data Migration Tasks page

1. Log on to the Data Management (DMS) console.

2. In the top navigation bar, click DTS.

3. In the left-side navigation pane, choose DTS (DTS) > Data Migration.

Console layout may vary. See Simple mode and Configure the DMS console based on your business requirements. Alternatively, go directly to the Data Migration Tasks page.

Step 2: Select the region

From the drop-down list next to Data Migration Tasks, select the region where the migration instance resides.

In the new DTS console, select the region in the upper-left corner.

Step 3: Configure source and destination databases

Click Create Task and configure the following parameters.

Task settings

Source Database

Destination Database

Step 4: Test connectivity

Click Test Connectivity and Proceed at the bottom of the page.

DTS automatically adds its server CIDR blocks to the whitelist of Alibaba Cloud database instances and to the security group rules of ECS-hosted databases. For self-managed databases in data centers or on third-party cloud providers, manually add the DTS CIDR blocks to the database whitelist. See Add the CIDR blocks of DTS servers to the security settings of on-premises databases.

Step 5: Configure migration objects and advanced settings

Migration type

If you do not select Incremental Data Migration, do not write to the source instance during migration to maintain data consistency.

Processing mode for conflicting tables

Select objects

Select one or more objects from the Source Objects section and click to add them to the Selected Objects section.

You can select columns, tables, or schemas. If you select tables or columns, DTS does not migrate views, triggers, or stored procedures.

To rename a single object, right-click it in Selected Objects. See Map the name of a single object.

To rename multiple objects at once, click in the upper-right corner of Selected Objects. See Map multiple object names at a time.

Renaming an object may cause other objects that depend on it to fail migration.

To filter rows by condition, right-click a table in Selected Objects and specify a WHERE clause. See Use SQL conditions to filter data.

To select specific DML or DDL operations for a table, right-click the table in Selected Objects and select the operations. See SQL operations supported for incremental migration.

Advanced settings

For retry time, if multiple tasks share the same source or destination database, the most recently set value takes precedence. DTS charges for the instance during retry periods — release the instance promptly after migration completes.

Step 6: Run the precheck

Click Next: Save Task Settings and Precheck.

DTS runs a precheck before starting the task. To resolve failures:

• For failed items: click View Details, fix the issue, then click Precheck Again.

• For alert items that can be ignored: click Confirm Alert Details > Ignore > OK, then click Precheck Again.

Ignoring alert items may cause data inconsistency.

Step 7: Purchase the instance

Wait for the Success Rate to reach 100%, then click Next: Purchase Instance.

On the Purchase Instance page, select an Instance Class for the migration instance. Higher instance classes provide faster migration speeds. See Specifications of data migration instances.

Step 8: Start the task

Read and accept the Data Transmission Service (Pay-as-you-go) Service Terms, then click Buy and Start.

Monitor the migration progress in the task list.