One-way synchronization between PolarDB for MySQL clusters

Limits

Billing

Supported SQL operations

Procedure

1. Go to the data synchronization task list page in the destination region. You can do this in one of two ways.

   DTS console

   1. Log on to the DTS console.

   2. In the navigation pane on the left, click Data Synchronization.

   3. In the upper-left corner of the page, select the region where the synchronization instance is located.

   DMS console

   Note

   The actual steps may vary depending on the mode and layout of the DMS console. For more information, see Simple mode console and Customize the layout and style of the DMS console.

   1. Log on to the DMS console.

   2. In the top menu bar, choose Data + AI > DTS (DTS) > Data Synchronization.

   3. To the right of Data Synchronization Tasks, select the region of the synchronization instance.

2. Click Create Task to open the task configuration page.

3. Optional: In the upper-right corner of the page, click New Configuration Page.

   Note

   • If you are already on the new configuration page (the button in the upper-right corner is Back to Previous Version), you can skip this step.

   • Some parameters differ between the new and old configuration pages. We recommend using the new version.

4. Configure the source and destination databases.

   Warning

   After you select the source and destination instances, review the Limits at the top of the page. Otherwise, the task may fail or data inconsistency may occur.

   Section	Parameter	Description
   N/A	Task Name	DTS automatically generates a task name. We recommend that you specify a descriptive name for easy identification. The name does not need to be unique.
   Source Database	Select a DMS database instance.	Choose whether to use an existing instance as needed. If you use an existing instance, the database information is automatically filled in. You do not need to enter it again. If you do not use an existing instance, configure the database information below. Note In the DMS console, click Add DMS Database Instance to add a database instance. For more information, see Add an ApsaraDB database instance and Add a third-party or self-managed database instance. In the DTS console, you can add a database to DTS on the Database Connections page or the new configuration page. For more information, see Manage data connections.
   	Database Type	Select PolarDB for MySQL.
   	Connection Type	Select Alibaba Cloud Instance.
   	Instance Region	Select the region where the source PolarDB for MySQL cluster is located.
   	Replicate Data Across Alibaba Cloud Accounts	In this scenario, data is synchronized within the same Alibaba Cloud account. Select No.
   	PolarDB Cluster ID	Select the ID of the source PolarDB for MySQL cluster. Note The source and destination PolarDB for MySQL clusters can be the same or different. You can use DTS to migrate data between two PolarDB for MySQL clusters or within the same PolarDB for MySQL cluster.
   	Database Account	Enter the database account for the source PolarDB for MySQL cluster. The account must have read permissions on the synchronization objects.
   	Database Password	Enter the password for the specified database account.
   	Encryption	Select an option based on your business requirements. For more information about SSL encryption, see Configure SSL encryption.
   Destination Database	Select a DMS database instance.	Choose whether to use an existing instance as needed. If you use an existing instance, the database information is automatically filled in. You do not need to enter it again. If you do not use an existing instance, configure the database information below. Note In the DMS console, click Add DMS Database Instance to add a database instance. For more information, see Add an ApsaraDB database instance and Add a third-party or self-managed database instance. In the DTS console, you can add a database to DTS on the Database Connections page or the new configuration page. For more information, see Manage data connections.
   	Database Type	Select PolarDB for MySQL.
   	Connection Type	Select Alibaba Cloud Instance.
   	Instance Region	Select the region where the destination PolarDB for MySQL cluster is located.
   	PolarDB Cluster ID	Select the ID of the destination PolarDB for MySQL cluster. Note If the destination cluster is a multi-master cluster (Limitless) and its read/write mode is read-write (automatic read/write splitting), the cluster uses a database and table routing mechanism. You must add the primary node that hosts the destination objects to the read/write endpoint, or select all primary nodes. Before you select a node, we recommend that you fully evaluate the routing impact. For more information, see Configure a database proxy.
   	Database Account	Enter the database account for the destination PolarDB for MySQL cluster. The account must have read permissions on the destination database. Important We recommend using a privileged account.
   	Database Password	Enter the password for the specified database account.
   	Encryption	Select an option based on your business requirements. For more information about SSL encryption, see Configure SSL encryption.

5. After completing the configuration, click Test Connection and Proceed at the bottom of the page.

   If the source or destination database is an Alibaba Cloud database instance, such as an RDS for MySQL instance or an ApsaraDB for MongoDB instance, DTS automatically adds the IP address of the DTS service for the corresponding region to the whitelist of the Alibaba Cloud database instance. If the source or destination database is a self-managed database on an ECS instance, DTS automatically adds the IP address of the DTS service for the corresponding region to the security rules of the ECS instance. You must also ensure that the self-managed database does not restrict access from the ECS instance. If the database is deployed in a cluster on multiple ECS instances, you must manually add the IP address of the DTS service for the corresponding region to the security rules of each of the other ECS instances. If the source or destination database is a self-managed database in an IDC or a database from another cloud provider, you must manually add the IP address of the DTS service for the corresponding region to allow access from the DTS servers. For more information about the IP addresses of the DTS service, see IP address blocks of DTS servers.

   Warning

   Adding the public IP address blocks of the DTS service, either automatically or manually, may pose security risks. Using this product, you acknowledge that you understand and accept the potential security risks and that you must implement basic security measures. These measures include, but are not limited to, strengthening password security, limiting the ports open to each CIDR block, using authentication for internal API calls, and regularly checking and restricting unnecessary CIDR blocks. Alternatively, you can connect through a private network using a leased line, VPN Gateway, or Smart Access Gateway.

6. Configure the task objects.

   1. On the Configure Objects page, specify the objects to synchronize.

      Parameter	Description
      Synchronization Types	DTS always selects Incremental Data Synchronization. By default, you must also select Schema Synchronization and Full Data Synchronization. After the precheck, DTS initializes the destination cluster with the full data of the selected source objects, which serves as the baseline for subsequent incremental synchronization.
      Method to Migrate Triggers in Source Database	Select a method to synchronize triggers based on your business requirements. If the synchronization objects do not involve triggers, you do not need to configure this parameter. For more information, see Configure a method to synchronize or migrate triggers. Note This parameter is available only if you select Schema Synchronization for Synchronization Types.
      Synchronization Topology	In this example, One-way Synchronization is selected.
      Processing Mode of Conflicting Tables	Precheck and Report Errors: Checks for tables with the same names in the destination database. If any tables with the same names are found, an error is reported during the precheck and the data synchronization task does not start. Otherwise, the precheck is successful. Note If you cannot delete or rename the table with the same name in the destination database, you can map it to a different name in the destination. For more information, see Database Table Column Name Mapping. Ignore Errors and Proceed: Skips the check for tables with the same name in the destination database. Warning Selecting Ignore Errors and Proceed may cause data inconsistency and put your business at risk. For example: If the table schemas are consistent and a record in the destination database has the same primary key or unique key value as a record in the source database: During full data synchronization, DTS retains the destination record and skips the source record. During incremental synchronization, DTS overwrites the destination record with the source record. If the table schemas are inconsistent, data initialization may fail. This can result in only partial data synchronization or a complete synchronization failure. Use with caution.
      Whether to migrate Event	Specify whether to synchronize events from the source database as required. If you select Yes, you must also meet the relevant requirements and perform subsequent operations. For more information, see Synchronize or migrate events.
      Source Objects	In the Source Objects box, click the objects, and then click to move them to the Selected Objects box. Note You can select objects at the database, table, or column level. If you select only tables or columns, DTS does not synchronize other object types (such as views, triggers, and stored procedures).
      Selected Objects	To rename a single object in the destination instance, right-click the object in the Selected Objects box. For more information, see Map a single object name. To rename multiple objects in bulk, click Batch Edit in the upper-right corner of the Selected Objects box. For more information, see Map multiple object names in bulk. Note To select SQL operations for a specific database or table, right-click the object in the Selected Objects pane and select the desired SQL operations in the dialog box that appears. For a list of supported operations, see Supported SQL operations. To set a WHERE clause to filter data, right-click the table you want to filter in the Selected Objects pane and set the filter condition in the dialog box that appears. For more information, see Configure filter conditions.

   2. Click Next: Advanced Settings.

      Parameter	Description
      Dedicated Cluster for Task Scheduling	By default, DTS uses a shared cluster for tasks, so you do not need to make a selection. For greater task stability, you can purchase a dedicated cluster to run the DTS synchronization task. For more information, see What is a DTS dedicated cluster?.
      Select the engine type of the destination database	Select the engine type of the destination database based on your business requirements. InnoDB: The default storage engine. X-Engine: An online transaction processing (OLTP) database storage engine.
      Copy the temporary table of the Online DDL tool that is generated in the source table to the destination database.	If the source database uses Data Management (DMS) or gh-ost for online DDL changes, choose whether to synchronize the temporary tables generated during these operations. Important DTS tasks do not currently support online DDL changes performed by tools like pt-online-schema-change. Using such tools will cause the DTS task to fail. Yes: Synchronizes the temporary tables generated by online DDL changes. Note If the data of temporary tables generated by online DDL changes is too large, it may cause synchronization latency. No, Adapt to DMS Online DDL: Does not synchronize temporary tables generated by online DDL changes. Instead, it synchronizes only the original DDL statements executed in Data Management (DMS). Note This approach will cause table locks on the destination database. No, Adapt to gh-ost: Does not the synchronize temporary tables generated by online DDL changes. Instead, it synchronizes only the original DDL statements executed by gh-ost. You can use default or custom regular expressions for gh-ost shadow and trash tables. Note This approach will cause table locks on the destination database.
      Whether to Migrate Accounts	Select whether to synchronize the account information of the source database based on your business requirements. If you select Yes, you must also select the accounts to be synchronized and confirm their permissions. For more information about authorization, see Migrate database accounts.
      Retry Time for Failed Connections	If the connection to the source or destination database fails after the synchronization task starts, DTS reports an error and immediately begins to retry the connection. The default retry duration is 720 minutes. You can customize the retry time to a value from 10 to 1,440 minutes. We recommend a duration of 30 minutes or more. If the connection is restored within this period, the task resumes automatically. Otherwise, the task fails. Note If multiple DTS instances (e.g., Instance A and B) share a source or destination, DTS uses the shortest configured retry duration (e.g., 30 minutes for A, 60 for B, so 30 minutes is used) for all instances. DTS charges for task runtime during connection retries. Set a custom duration based on your business needs, or release the DTS instance promptly after you release the source/destination instances.
      Retry Time for Other Issues	If a non-connection issue (e.g., a DDL or DML execution error) occurs, DTS reports an error and immediately retries the operation. The default retry duration is 10 minutes. You can also customize the retry time to a value from 1 to 1,440 minutes. We recommend a duration of 10 minutes or more. If the related operations succeed within the set retry time, the synchronization task automatically resumes. Otherwise, the task fails. Important The value of Retry Time for Other Issues must be less than that of Retry Time for Failed Connections.
      Enable Throttling for Full Data Synchronization	During full data synchronization, DTS consumes read and write resources from the source and destination databases, which can increase their load. To mitigate pressure on the destination database, you can limit the migration rate by setting Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s). Note This parameter is available only if Synchronization Types is set to Full Data Synchronization. You can also adjust the rate of full data synchronization when the synchronization instance is running.
      Enable Throttling for Incremental Data Synchronization	You can also limit the incremental synchronization rate to reduce pressure on the destination database by setting RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s).
      Whether to delete SQL operations on heartbeat tables of forward and reverse tasks	Choose whether DTS writes heartbeat SQL information to the source database while the instance is running. Yes: Does not write heartbeat SQL information to the source database. The DTS instance may display latency. No: Writes heartbeat SQL information to the source database. This may interfere with source database operations like physical backups and cloning.
      Environment Tag	You can select an environment tag to identify the instance based on your business requirements. No selection is needed in this example.
      Configure ETL	Choose whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: Enables the ETL feature. Enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: Disables the ETL feature.
      Monitoring and Alerting	Choose whether to set up alerts. If the synchronization fails or the latency exceeds the specified threshold, DTS sends a notification to the alert contacts. No: No alerts are configured. Yes: Configures alerts. You must also set the alert threshold and alert contact. For more information, see Configure monitoring and alerting during task configuration.

   3. Click Data Verification to configure a data verification task.

      To use the data verification feature, see Configure data verification.

7. Save the task and perform a precheck.

   • To view the parameters for configuring this instance via an API operation, hover over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the tooltip.

   • If you have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.

   Note

   • Before a synchronization task starts, DTS performs a precheck. You can start the task only if the precheck passes.

   • If the precheck fails, click View Details next to the failed item, fix the issue as prompted, and then rerun the precheck.

   • If the precheck generates warnings:

     • For non-ignorable warning, click View Details next to the item, fix the issue as prompted, and run the precheck again.

     • For ignorable warnings, you can bypass them by clicking Confirm Alert Details, then Ignore, and then OK. Finally, click Precheck Again to skip the warning and run the precheck again. Ignoring precheck warnings may lead to data inconsistencies and other business risks. Proceed with caution.

8. When the Success Rate reaches 100%, click Next: Purchase Instance.

9. Purchase the instance.

   1. On the Purchase page, select the billing method and link specifications for the data synchronization instance. For more information, see the following table.

      Category	Parameter	Description
      New Instance Class	Billing Method	Subscription: You pay upfront for a specific duration. This is cost-effective for long-term, continuous tasks. Pay-as-you-go: You are billed hourly for actual usage. This is ideal for short-term or test tasks, as you can release the instance at any time to save costs.
      	Resource Group Settings	The resource group to which the instance belongs. The default is default resource group. For more information, see What is Resource Management?.
      	Instance Class	DTS offers synchronization specifications at different performance levels that affect the synchronization rate. Select a specification based on your business requirements. For more information, see Data synchronization link specifications.
      	Subscription Duration	In subscription mode, select the duration and quantity of the instance. Monthly options range from 1 to 9 months. Yearly options include 1, 2, 3, or 5 years. Note This option appears only when the billing method is Subscription.

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

   3. Click Buy and Start, and then click OK in the OK dialog box.

      You can monitor the task progress on the data synchronization page.