PolarDB:Migrate data from a PolarDB for MySQL cluster to an ApsaraDB RDS for MySQL instance

Source database requirements

• Tables to be migrated must have a PRIMARY KEY or UNIQUE constraint with all fields unique. Without this, the destination may contain duplicate records.

• The source database server must have sufficient outbound bandwidth. Low bandwidth reduces migration speed.

• When migrating with object renaming (renaming tables or columns in the destination), a single task supports up to 1,000 tables. For more than 1,000 tables, either split into multiple tasks or migrate the entire database.

• Read-only nodes of the source PolarDB for MySQL cluster cannot be migrated.

Binary log requirements (incremental migration only)

• Binary logging must be enabled and loose_polar_log_bin must be set to on. If not configured, the precheck fails and the task cannot start.

• Binary logs incur storage charges when enabled on a PolarDB for MySQL cluster.

• Retain binary logs for the following minimum periods: If binary logs are purged before DTS reads them, the task fails. After full migration completes, you can reduce the retention period to more than 24 hours.

  • Incremental-only migration: more than 24 hours

  • Full data + incremental migration: at least 7 days

Operational restrictions during migration

• During schema migration and full data migration, do not perform DDL operations on the source database. DDL changes during this phase cause the task to fail.

• During full-only migration (no incremental), do not write to the source database. Writes cause data inconsistency between source and destination.

• DTS temporarily disables foreign key constraint checks and cascade operations at the session level during full and incremental migration. If you perform cascade or delete operations on the source during this time, data inconsistency may occur.

Other usage notes

• Full data migration uses concurrent INSERT operations, which creates table fragmentation in the destination. After migration, the destination tablespace is larger than the source tablespace.

• DTS uses ROUND(COLUMN, PRECISION) to read FLOAT and DOUBLE columns. Default precision is 38 digits for FLOAT and 308 digits for DOUBLE. Verify that these precision settings meet your requirements before migration.

• DTS retries failed tasks for up to 7 days. Before switching workloads to the destination, stop or release the migration task. Alternatively, run REVOKE to remove write permissions from the DTS accounts on the destination. Otherwise, a resumed failed task overwrites destination data with source data.

• DTS executes CREATE DATABASE IF NOT EXISTS \test\`` on the source database periodically to advance the binary log position.

• During schema migration, DTS migrates foreign keys from the source database to the destination database. DTS also changes the SECURITY attribute from DEFINER to INVOKER for views, stored procedures, and stored functions. DTS does not migrate user information. To call these objects in the destination, grant the required read and write permissions to the INVOKER.

• If the source database name is invalid, DTS cannot automatically create the destination database. Manually create it in the ApsaraDB RDS for MySQL instance before configuring the task. See Manage databases.

• Migrate data during off-peak hours to reduce the impact on source and destination database performance.

Step 1: Go to the Data Migration Tasks page

1. Log on to the Data Management (DMS) console.Data Migration Tasks page of the new DTS console

2. In the top navigation bar, click DTS.

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

The navigation may vary depending on the DMS console mode and layout. See Simple mode and Customize the layout and style of the DMS console for details. You can also go directly to the Data Migration Tasks page in the DTS console.

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 instead.

Step 3: Create the task

Click Create Task to open the task configuration page.

Optional: If the Back to Previous Version button is not visible in the upper-right corner, click New Configuration Page to switch to the latest configuration UI. The new page is recommended because some parameters differ between versions.

Step 4: Configure source and destination databases

Configure the following parameters:

Source database (PolarDB for MySQL)

Destination database (ApsaraDB RDS for MySQL)

To register a database with DMS, click Create Template in the DMS console. To register with DTS, go to the Database Connections page. For registration instructions, see Register an Alibaba Cloud database instance. For self-managed or third-party cloud databases, see Register a database hosted on a third-party cloud service or a self-managed database. To manage DTS database connections, see Manage database connections.

Step 5: Test connectivity

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

DTS automatically adds its server CIDR blocks to the IP address 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 server CIDR blocks to the database whitelist. See Add the CIDR blocks of DTS servers.

Step 6: Select objects to migrate

On the Select Objects page, configure the migration scope.

Migration types

If you do not select Incremental Data Migration, do not write to the source database during migration to keep data consistent.

Other parameters

Step 7: Configure advanced settings

Click Next: Advanced Settings and configure as needed.

Step 8: Configure data verification (optional)

Click Next Step: Verification Configurations to set up data verification. See Configure data verification.

Step 9: Run the precheck

Click Next: Save Task Settings and Precheck.

To preview the API parameters for this task configuration, hover over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters.

DTS runs a precheck before the task starts. The task only starts after the precheck passes.

• If an item fails: click View Details next to the failed item, fix the issue, then click Precheck Again.

• If an alert is generated: if the alert cannot be ignored, fix the issue and rerun the precheck. If it can be ignored, click Confirm Alert Details > Ignore > OK > Precheck Again. Ignoring alerts may result in data inconsistency.

Step 10: Purchase the migration instance and start

Wait until the precheck success rate reaches 100%, then click Next: Purchase Instance.

1. On the Purchase Instance page, configure the instance class:

   Parameter	Description
   Resource Group Settings	Select the resource group for the migration instance. Default: default resource group. See What is Resource Management?.
   Instance Class	Select a class based on your required migration speed. See Specifications of data migration instances.

2. Read and accept the Data Transmission Service (Pay-as-you-go) Service Terms.

3. Click Buy and Start. Monitor task progress in the task list.