This topic describes how to configure two-way synchronization between PolarDB-X 2.0 instances by using Data Transmission Service (DTS).
Prerequisites
The source and destination PolarDB-X 2.0 Enterprise Edition instances that are compatible with MySQL 5.7 are created. The source and destination PolarDB-X 2.0 Enterprise Edition instances are not log engine instances that store multiple streams of binary logs.
The available storage space of the destination PolarDB-X 2.0 instance is larger than the total size of the data in the source PolarDB-X 2.0 instance.
Limits
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 the constraint check and cascade operations on foreign keys at the session level. If you perform the cascade update and delete operations on the source database during data synchronization, data inconsistency may occur.
Category | Description |
Category | Description |
Limits on the source database |
|
Other limits |
|
Usage notes | DTS updates the |
Billing
| Synchronization type | Task configuration fee |
| Synchronization type | Task configuration fee |
| Schema synchronization and full data synchronization | Free of charge. |
| Incremental data synchronization | Charged. For more information, see Billing overview. |
SQL operations that can be synchronized
Operation type | SQL statement |
Operation type | SQL statement |
DML | INSERT, UPDATE, and DELETE |
Permissions required for database accounts
The database accounts of the source and destination PolarDB-X 2.0 instances must be privileged accounts. For more information about how to create a database account and grant permissions to the database account, see Manage database accounts.
Procedure
Go to the Data Synchronization Tasks page.
Log on to the Data Management (DMS) console.
In the top navigation bar, click DTS.
In the left-side navigation pane, choose .
Operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Customize the layout and style of the DMS console.
You can also go to the Data Synchronization Tasks page of the new DTS console.
On the right side of Data Synchronization Tasks, select the region in which the data synchronization instance resides.
If you use the new DTS console, you must select the region in which the data synchronization instance resides in the top navigation bar.
Click Create Task. Configure the source and destination databases.
After you configure the source and destination databases, we recommend that you read the limits that are displayed on the page. Otherwise, the task may fail or data inconsistency may occur.
Section
Parameter
Description
Section
Parameter
Description
N/A
Task Name
The name of the DTS task. DTS automatically generates a task name. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to specify a unique task name.
Source Database
Select a DMS database instance
Select whether to use an existing instance.
If you select an existing instance, DTS automatically populates the parameters for the database.
If you do not select an existing instance, you must manually configure parameters for the database.
Database Type
The type of the source database. Select PolarDB-X 2.0.
Access Method
The access method of the source database. Select Alibaba Cloud Instance.
Instance Region
The region in which the source PolarDB-X 2.0 instance resides.
Replicate Data Across Alibaba Cloud Accounts
Specifies whether to synchronize data across Alibaba Cloud accounts. In this example, No is selected.
Instance ID
The ID of the source PolarDB-X 2.0 instance.
Database Account
The privileged account of the source PolarDB-X 2.0 instance.
Database Password
The password of the database account.
Destination Database
Select a DMS database instance
Select whether to use an existing instance.
If you select an existing instance, DTS automatically populates the parameters for the database.
If you do not select an existing instance, you must manually configure parameters for the database.
Database Type
The type of the destination database. Select PolarDB-X 2.0.
Access Method
The access method of the destination database. Select Alibaba Cloud Instance.
Instance Region
The region in which the destination PolarDB-X 2.0 instance resides.
Instance ID
The ID of the destination PolarDB-X 2.0 instance.
Database Account
The privileged account of the destination PolarDB-X 2.0 instance.
Database Password
The password of the database account.
In the lower part of the page, click Test Connectivity and Proceed.
If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance, and you must make sure that the ECS instance can access the database. If the database is deployed on multiple ECS instances, you must manually add the CIDR blocks of DTS servers to the security group rules of each ECS instance. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the whitelist of the database to allow DTS to access the database. For more information, see Add the CIDR blocks of DTS servers.
If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database or instance, or to the ECS security group rules, security risks may arise. Therefore, before you use DTS to synchronize data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
Configure the objects to be synchronized and the advanced settings.
Parameter
Description
Parameter
Description
Synchronization Types
The synchronization types. By default, Incremental Data Synchronization is selected. You must also select Schema Synchronization and Full Data Synchronization. After the precheck is complete, DTS synchronizes the historical data of the selected objects from the source database to the destination database. The historical data is the basis for subsequent incremental synchronization.
Processing Mode of Conflicting Tables
Precheck and Report Errors: checks whether the destination database contains tables that have the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck and the data synchronization task cannot be started.
If the source and destination databases contain identical table names and the tables in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the tables that are synchronized to the destination database. For more information, see Map object names.
Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases.
If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to the following potential risks:
If the source and destination databases have the same schema and a data record in the destination database has the same primary key value or unique key value as a data record in the source database:
During full data synchronization, DTS does not synchronize the data record to the destination database. The existing data record in the destination database is retained.
During incremental data synchronization, DTS synchronizes the data record to the destination database. The existing data record in the destination database is overwritten.
If the source and destination databases have different schemas, data may fail to be initialized. In this case, only some columns are synchronized, or the data synchronization task fails. Proceed with caution.
Synchronization Topology
The synchronization topology of the data synchronization task. Select Two-way Synchronization.
Exclude DDL Operations
DDL operations cannot be synchronized in this scenario. Select Yes.
Conflict Resolution Policy
Select a conflict resolution policy based on your business requirements.
TaskFailed
If a conflict occurs during data synchronization, the data synchronization task reports an error and exits the process. The task enters a failed state, and you must manually resolve the conflict.
Ignore
If a conflict occurs during data synchronization, the data synchronization task ignores the current statement and continues the process. The conflicting records in the destination database are used.
Overwrite
If a conflict occurs during data synchronization, the conflicting records in the destination database are overwritten.
Source Objects
Select one or more objects from the Source Objects section and click the
icon to move the objects to the Selected Objects section. You can select columns, tables, or databases as the objects to be synchronized. If you select tables or columns as the objects to be synchronized, DTS does not synchronize other objects such as views, triggers, and stored procedures to the destination database.
Selected Objects
To rename an object that you want to synchronize to the destination instance, right-click the object in the Selected Objects section. For more information, see the Map the name of a single object section of the "Map object names" topic.
To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see the Map multiple object names at a time section of the "Map object names" topic.
To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to synchronize. For more information about the SQL operations that can be synchronized, see the SQL operations that can be synchronized section of this topic.
To specify WHERE conditions to filter data, right-click an object in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Set filter conditions.
If you use the object name mapping feature to rename an object, other objects that are dependent on the object may fail to be synchronized.
Click Next: Advanced Settings to configure advanced settings.
Parameter
Description
Parameter
Description
Select the dedicated cluster used to schedule the task
By default, DTS schedules tasks to shared clusters. You do not need to configure this parameter. You can purchase a dedicated cluster of specific specifications to run DTS data synchronization tasks. For more information, see What is a DTS dedicated cluster.
Set Alerts
Specifies whether to configure alerting for the data synchronization task. If the task fails or the synchronization latency exceeds the specified threshold, alert contacts will receive notifications. Valid values:
No: does not configure alerting.
Yes: configures alerting. In this case, you must also configure the alert threshold and alert contacts. For more information, see Configure monitoring and alerting.
Retry Time for Failed Connections
The retry time range for failed connections. If the source or destination database fails to be connected after the data synchronization task is started, DTS immediately retries a connection within the time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set this parameter to a value greater than 30. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails.
If you specify different retry time ranges for multiple data synchronization tasks that have the same source or destination database, the shortest retry time range takes precedence.
When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
The wait time before a retry when other issues occur in the source and destination databases.
The retry time range for other issues. For example, if DDL or DML operations fail to be performed after the data migration task is started, DTS immediately retries the operations within the retry time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set the parameter to a value greater than 10. If the failed operations are successfully performed within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails.
The value of the The wait time before a retry when other issues occur in the source and destination databases parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Full Data Migration
During full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the load on the database servers. You can configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters for full data synchronization tasks to reduce the load on the destination database server.
This parameter is displayed only if Full Data Synchronization is selected for the Synchronization Types parameter.
Enable Throttling for Incremental Data Synchronization
Specifies whether to enable throttling for incremental data synchronization. You can enable throttling for incremental data synchronization based on your business requirements. To configure throttling, you must configure the RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s) parameters. This reduces the load on the destination database server.
Whether to delete SQL operations on heartbeat tables of forward and reverse tasks
Specifies whether to write SQL operations on heartbeat tables to the source database while the DTS instance is running.
Yes: does not write SQL operations on heartbeat tables. In this case, a latency of the DTS instance may be displayed.
No: writes SQL operations on heartbeat tables. In this case, specific features such as physical backup and cloning of the source database may be affected.
Save the task settings and run a precheck.
To view the parameters to be specified when you call the relevant API operation to configure the DTS task, move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters.
If you do not need to view or have viewed the parameters, click Next: Save Task Settings and Precheck in the lower part of the page.
Before you can start the data synchronization task, DTS performs a precheck. You can start the data synchronization task only after the task passes the precheck.
If the task fails to pass the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, run a precheck again.
If an alert is triggered for an item during the precheck:
If an alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issue. Then, run a precheck again.
If an alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur and your business may be exposed to potential risks.
Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.
On the Purchase Instance page, configure the Billing Method and Instance Class parameters for the data synchronization instance. The following table describes the parameters.
Section
Parameter
Description
Section
Parameter
Description
New Instance Class
Billing Method
Subscription: You pay for your subscription when you create an instance. The subscription billing method is more cost-effective than the pay-as-you-go billing method for long-term use.
Pay-as-you-go: A pay-as-you-go instance is billed on an hourly basis. We recommend that you select the pay-as-you-go billing method for short-term use. If you no longer require a pay-as-you-go instance, you can release the instance to reduce costs.
Resource Group
The resource group to which the instance belongs. Default value: default resource group. For more information, see What is Resource Management?
Instance Class
DTS provides various synchronization specifications that provide different performance. The synchronization speed varies based on the synchronization specifications that you select. You can select a synchronization specification based on your business requirements. For more information, see Specifications of data synchronization instances.
Duration
If you select the subscription billing method, set the subscription duration and the number of instances that you want to create. The subscription duration can be one to nine months, one year, two years, three years, or five years.
This parameter is displayed only if you select the subscription billing method.Subscription
Read and select the Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.
