Synchronize data from a PolarDB-X 1.0 instance to a PolarDB-X 2.0 instance - Data Transmission Service

This topic describes how to use Data Transmission Service (DTS) to synchronize data from a PolarDB-X 1.0 instance to a PolarDB-X 2.0 instance.

Prerequisites

The source PolarDB-X 1.0 instance must use RDS for MySQL as its storage class. This includes private custom RDS and separately purchased RDS instances. PolarDB for MySQL is not currently supported.
A destination PolarDB-X 2.0 instance and a database to receive the data are created. For more information, see Create an instance (Starter Edition) and Create a database.
The storage space of the destination instance must be larger than the storage space used by the source instance.

Notes

Note

During schema synchronization, DTS synchronizes foreign keys from the source database to the destination database.
During full data synchronization and incremental data synchronization, DTS temporarily disables constraint checks and foreign key cascade operations at the session level. Data inconsistency may occur if cascade update or delete operations are performed on the source database while the task is running.

Type	Description
Source database limitations	Tables to be synchronized must have a PRIMARY KEY constraint or a UNIQUE constraint. Schema synchronization is not supported for tables that have only a UNIQUE constraint. Use a PRIMARY KEY constraint. The fields in the key must be unique. Otherwise, duplicate data may appear in the destination database. If you synchronize data at the table level and need to edit the objects, such as mapping table or column names, a single synchronization task supports up to 1,000 tables. If you exceed this limit, an error is reported after you submit the task. In this case, split the tables into multiple tasks or configure a task to synchronize the entire database. Binary logs of the RDS for MySQL instances attached to the PolarDB-X 1.0 instance: Binary logging is enabled by default. For more information, see View instance parameters to confirm that binlog_row_image is set to full. Otherwise, an error is reported during the precheck, and the data synchronization task cannot start. For an incremental data synchronization task, DTS requires that the local binary logs of the source database are retained for more than 24 hours. For a task that includes both full and incremental data synchronization, DTS requires that the local binary logs of the source database are retained for at least 7 days. You can change the retention period to more than 24 hours after the full synchronization is complete. Otherwise, the task may fail because DTS cannot obtain the binary logs. In extreme cases, this may cause data inconsistency or data loss. Issues caused by a binary log retention period that is shorter than the required period are not covered by the DTS Service-Level Agreement (SLA). Source database operation limitations: To switch the network type of the PolarDB-X 1.0 instance during synchronization, update the network connection information of the synchronization link after the switch is successful. During synchronization, do not perform operations on the source instance such as scaling (for example, scaling its attached ApsaraDB RDS for MySQL instance, or changing the distribution of physical tables that correspond to logical tables in ApsaraDB RDS for MySQL even if the ApsaraDB RDS for MySQL instance is not scaled), migrating hot tables, changing the shard key, or making DDL changes. Otherwise, the data synchronization task will fail or data inconsistencies will occur. If you change the partition key of a source table, and the primary key of the corresponding destination table does not include the partition key, data loss may occur in the destination database. Reason: A PolarDB-X 1.0 instance has multiple ApsaraDB RDS for MySQL instances attached to it. DTS maintains independent synchronization links for each ApsaraDB RDS for MySQL instance. Changing a partition key causes data to be deleted from one ApsaraDB RDS for MySQL instance and inserted into another. Because these links execute independently, the order of the DELETE and INSERT operations can be disrupted. If the primary key of the destination database does not include the partition key, a DELETE operation that is executed later can incorrectly delete the newly inserted data. Recommendation: To prevent data loss from out-of-order operations, ensure the primary key of the destination table includes the partition key columns of the source table. If you perform only full data synchronization, do not write new data to the source instance. Otherwise, data inconsistency occurs between the source and destination. To maintain real-time data consistency, select schema synchronization, full data synchronization, and incremental data synchronization. Do not run DDL operations that change database or table schemas during schema synchronization or full synchronization. Otherwise, the synchronization task fails. Note During full synchronization, DTS queries the source database. This creates metadata locks that may block DDL operations on the source database. The source PolarDB-X 1.0 instance must be version 5.2 or later.
Other limitations	The storage type of the PolarDB-X 1.0 instance must be RDS for MySQL. This includes private custom RDS and separately purchased RDS. PolarDB for MySQL is not supported. Synchronization tasks for PolarDB-X 1.0 are distributed. Each attached RDS for MySQL instance corresponds to a synchronization subtask. You can view the status of subtasks on the Task Topology page. Incremental data synchronization relies on continuous XA transactions in the source PolarDB-X 1.0 instance to ensure data consistency. If this continuity is disrupted, for example when modifying synchronization objects or during disaster recovery of the incremental data capture module, uncommitted XA transactions may be lost. Before you synchronize data, evaluate the performance of the source and destination databases. Synchronize data during off-peak hours. Otherwise, DTS consumes read and write resources on the source and destination databases during full data synchronization, which may increase the database load. Because full data synchronization runs INSERT operations concurrently, fragmentation occurs in the destination tables. After full synchronization is complete, the storage space used by the destination tables is larger than that of the source tables. Verify that the synchronization precision that DTS uses for columns of the FLOAT or DOUBLE data type meets your business requirements. DTS reads the values of columns of these two data types using `ROUND(COLUMN,PRECISION)`. If you do not specify a precision, DTS sets the precision for columns of the FLOAT data type to 38 digits and the precision for columns of the DOUBLE data type to 308 digits. DTS attempts to resume failed synchronization tasks within seven days. Therefore, before you switch your services to the destination instance, you must end or release the task, or use the `revoke` command to revoke the write permissions of the account that DTS uses to access the destination instance. Otherwise, the data in the source instance overwrites the data in the destination instance after the task is automatically resumed. If a task fails, DTS support staff will attempt to restore it within eight hours. During restoration, they may restart the task or adjust its parameters. Note Only DTS task parameters are modified—not database parameters. Parameters that may be adjusted include those listed in Modify instance parameters.

Billing

Synchronization type	Pricing
Schema synchronization and full data synchronization	Free of charge.
Incremental data synchronization	Charged. For more information, see Billing overview.

SQL operations supported for incremental synchronization

Operation type	SQL operations
DML	INSERT, UPDATE, DELETE

Permissions required for database accounts

Database	Required permissions	Method to create an account and grant permissions
Source PolarDB-X 1.0 instance	Read permission on the synchronization objects.	Account Management
Destination PolarDB-X 2.0 instance	Read and write permissions on the destination database that contains the synchronization objects.	Manage database accounts

Procedure

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 DMS console layout and style.
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.
Click Create Task to open the task configuration page.

Configure the source and destination databases.

Category	Configuration	Description
None	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 Existing Connection	Select the registered database instance with DTS from the drop-down list. The database information below is automatically configured. Note In the DMS console, this configuration item is Select a DMS database instance. If you have not registered the database instance or do not need to use a registered instance, manually configure the database information below.
	Database Type	Select PolarDB-X 1.0.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source PolarDB-X 1.0 instance resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, data is synchronized between instances under the same Alibaba Cloud account. Select No.
	Instance ID	Select the ID of the source PolarDB-X 1.0 instance.
	Database Account	Enter the database account of the source PolarDB-X 1.0 instance.
	Database Password	Enter the password for the specified database account.
Destination Database	Select Existing Connection	Select the registered database instance with DTS from the drop-down list. The database information below is automatically configured. Note In the DMS console, this configuration item is Select a DMS database instance. If you have not registered the database instance or do not need to use a registered instance, manually configure the database information below.
	Database Type	Select PolarDB-X 2.0.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination PolarDB-X 2.0 instance resides.
	Instance ID	Select the ID of the destination PolarDB-X 2.0 instance.
	Database Account	Enter the database account of the destination PolarDB-X 2.0 instance.
	Database Password	Enter the password for the specified database account.

After you complete the configuration, click Test Connectivity and Proceed at the bottom of the page.
Note
Ensure that the IP address blocks of the DTS service are added to the security settings of the source and destination databases, either automatically or manually, to allow access from DTS servers. For more information, see Add the IP address whitelist of DTS servers.

Configure the task objects.

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

Configuration	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.
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.
Capitalization of Object Names in Destination Instance	Configure the case-sensitivity policy for database, table, and column names in the destination instance. By default, the DTS default policy is selected. You can also choose to use the default policy of the source or destination database. For more information, see Case policy for destination object names.
Source Objects	In the Source Objects box, select the object that you want to synchronize, and then click the icon to move it to the Selected Objects box. Note We recommend that you select objects at the table level. If you select an entire database as a synchronization object, changes to add or delete tables in the source database are not synchronized to the destination database.
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 set a WHERE clause to filter data, right-click the table in the Selected Objects box and set the filter condition in the dialog box that appears. For more information about how to set the condition, see Set filter conditions. If you use the object name mapping feature, the synchronization of other objects that depend on the mapped object may fail.

Click Next: Advanced Settings.

Configuration	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?.
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).
Environment Tag	If required, you can select an environment tag to identify the instance.
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 notifications. For more information, see Configure monitoring and alerting during task configuration.

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.

Purchase the instance.

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

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.

Read and select the checkbox for Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start, and then click OK in the OK dialog box.
You can monitor the task progress on the data synchronization page.