PolarDB:Synchronize data from PolarDB for MySQL to RDS for MySQL

Source database limitations

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

• When you select tables as the synchronization objects and need to edit them (such as renaming tables or columns), a single task supports up to 1,000 tables. For more than 1,000 tables, configure multiple tasks or synchronize at the database level.

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

DDL operations during synchronization

• Do not use pt-online-schema-change for DDL operations on source tables during synchronization. This may cause the task to fail.

• If DTS is the only writer to the destination database, you can use Data Management (DMS) to perform online DDL operations on source tables. See Perform lock-free operations.

• If tools other than DTS also write to the destination, DMS online DDL operations may cause data loss in the destination.

RENAME TABLE risk

If you select a table (not a database) as the synchronization object and rename it during synchronization, data for that table stops being synchronized. To avoid this, select the entire database as the synchronization object and ensure that both the pre-rename and post-rename database names are included in the selected objects.

Full data synchronization performance

DTS uses read and write resources on both the source and destination during initial full data synchronization. Schedule synchronization during off-peak hours to minimize load. Concurrent INSERT operations during full synchronization cause table fragmentation in the destination, so the destination tablespace will be larger than the source after full synchronization completes.

Foreign key behavior

• During schema synchronization, DTS synchronizes foreign keys from the source to the destination.

• During full and incremental data synchronization, DTS temporarily disables constraint checks and cascade operations on foreign keys at the session level. Cascade update or delete operations on the source during synchronization may cause data inconsistency.

Step 1: Open the Data Synchronization Tasks page

1. Log in 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 Synchronization.

Navigation options vary based on your DMS console mode. See Simple mode or Customize the layout and style of the DMS console. You can also go directly to the Data Synchronization Tasks page.

Step 2: Create a task

1. Select the region where the synchronization instance will reside.

   In the new DTS console, select the region in the top navigation bar.

2. Click Create Task.

3. (Optional) If the Back to Previous Version button is not displayed, click New Configuration Page in the upper-right corner. Use the new configuration page when available — some parameters differ between versions.

Step 3: Configure source and destination databases

Source database parameters:

Destination database parameters:

Step 4: Test connectivity

Click Test Connectivity and Proceed.

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

Step 5: Select objects to synchronize

On the Select Objects page, configure the following parameters:

Step 6: Configure advanced settings

Click Next: Advanced Settings and configure the following:

Step 7: Configure data verification (optional)

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

Step 8: Run the precheck

Click Next: Save Task Settings and Precheck.

To preview the OpenAPI parameters for this task, hover over the button and click Preview OpenAPI parameters.

Before the precheck runs, verify the following to reduce the risk of failure:

• Binary logging is enabled and loose_polar_log_bin is set to on

• The source account has read permissions; the destination account has read and write permissions

• Binary log retention meets the minimums listed in the Prerequisites section

• Source tables have PRIMARY KEY or UNIQUE constraints

The task starts only after the precheck passes.

• If an item fails, click View Details to review the cause, fix the issue, then click Precheck Again.

• If an alert can be safely ignored, click Confirm Alert Details > Ignore > OK, then click Precheck Again. Ignoring alerts may result in data inconsistency.

Step 9: Purchase a synchronization instance

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

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

The synchronization task appears in the task list. Monitor its progress from there.

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