Data synchronization between AnalyticDB for MySQL 3.0 clusters - Data Transmission Service

This topic describes how to use Data Transmission Service (DTS) to synchronize data between AnalyticDB for MySQL 3.0 clusters.

Applicability

A destination AnalyticDB for MySQL 3.0 cluster has been created. The storage space of the destination cluster must be larger than the total size of the data in the source AnalyticDB for MySQL 3.0 cluster.
The source AnalyticDB for MySQL 3.0 cluster has the change data capture (CDC) feature enabled, and you have enabled binary logging for the tables that you want to synchronize.
Note
- If the kernel version of an AnalyticDB for MySQL 3.0 cluster is earlier than 3.2.1.0, you must first upgrade the kernel version.
- XUANWU_V2 tables do not support binary logging. Therefore, DTS does not support data synchronization or incremental migration for XUANWU_V2 tables between AnalyticDB for MySQL clusters.

Precautions

Note

During schema synchronization, DTS does not synchronize 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.

Type	Description
Source database limits	Bandwidth requirements: The server that hosts the source database must have sufficient outbound bandwidth. Otherwise, the data synchronization speed is affected. The AnalyticDB for MySQL 3.0 cluster must use kernel version 3.2.1.0 or later. The tables to be synchronized must have custom primary keys, and the fields must be unique. Otherwise, duplicate data may appear in the destination database. Note If the primary key of a table to be synchronized is the auto-generated `__adb_auto_id__`, DTS does not support data synchronization for that table. During schema synchronization and full data synchronization, do not perform DDL operations that change the schema of a database or table. Otherwise, the data synchronization task fails.
Other limits	A data synchronization instance can synchronize only one table. To synchronize multiple tables, create multiple data synchronization instances. The destination database must have a custom primary key, or you must configure a Primary Key Column in the Configurations for Databases, Tables, and Columns step. Otherwise, the data synchronization may fail. Data validation is not supported. You cannot modify synchronization objects after they are configured. If a data synchronization task is paused for more than one day, the binary logs of the source AnalyticDB for MySQL 3.0 cluster may expire. This may prevent the task from being resumed. While the data synchronization task is running, do not disable binary logging for the source AnalyticDB for MySQL 3.0 cluster. Otherwise, the task fails and cannot be recovered. If a task fails because you disabled binary logging, you must create a new task. Due to usage limits in AnalyticDB for MySQL 3.0 clusters, a DTS instance may experience delays if a node's disk space usage exceeds 80%. Therefore, you should estimate the required storage space in advance based on the objects to be synchronized to ensure that the destination cluster has sufficient storage space. If the destination AnalyticDB for MySQL 3.0 cluster is being backed up while the DTS task is running, the task fails. Initial full data synchronization involves concurrent INSERT operations, which cause table fragmentation in the destination database. As a result, the storage space occupied by the tables in the destination database is larger than that in the source database after the initial full synchronization is complete. During initial full data synchronization, DTS consumes read and write resources from both the source and destination databases. This may increase the database load. Before you synchronize data, evaluate the performance of the source and destination databases. Perform data synchronization during off-peak hours. For example, synchronize data when the CPU load of both the source and destination databases is below 30%. If the instance fails, DTS helpdesk will try to recover the instance within 8 hours. During the recovery process, the instance may be restarted and its parameters may be adjusted. Note When parameters are adjusted, only the parameters of the DTS instance are modified, not the parameters of the database. The parameters that can be modified include but are not limited to those described in Modify instance parameters.

Billing

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

Supported SQL operations

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE Note When data is written to an AnalyticDB for MySQL 3.0 cluster, UPDATE statements are automatically converted to REPLACE INTO statements. If the primary key is updated, the statement is converted to a DELETE statement and an INSERT statement.
DDL	ADD COLUMN, DROP COLUMN

Permissions required for database accounts

Database	Required permission	How to create accounts and grant permissions
Source AnalyticDB for MySQL 3.0 cluster	Read permissions on the tables to be synchronized.	Create a database account
Destination AnalyticDB for MySQL 3.0 cluster	Read and write permissions on the destination database.	Create a database account

Procedure

Use one of the following methods to go to the Data Synchronization page and select the region in which the data synchronization instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Synchronization.
3. In the upper-left corner of the page, select the region in which the data synchronization task resides.
DMS console
Note
The actual 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.
1. Log on to the DMS console.
2. In the top navigation bar, move the pointer over Data + AI and choose DTS (DTS) > Data Synchronization.
3. From the drop-down list to the right of Data Synchronization Tasks, select the region in which the data synchronization instance resides.
Click Create Task to go to the task configuration page.

Configure the source and destination databases. The following table describes the parameters.

Category	Configuration	Description
None	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 Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	Select AnalyticDB for MySQL 3.0.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source AnalyticDB for MySQL 3.0 cluster resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database of the current Alibaba Cloud account is used. Select No.
	Instance ID	Select the ID of the source AnalyticDB for MySQL 3.0 cluster.
	Database Account	The database account of the source AnalyticDB for MySQL 3.0 cluster. For permission requirements, see Permissions required for database accounts.
	Database Password	The password that is used to access the database.
Destination Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	Select AnalyticDB for MySQL 3.0.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination AnalyticDB for MySQL 3.0 cluster resides.
	Instance ID	Select the ID of the destination AnalyticDB for MySQL 3.0 cluster.
	Database Account	Enter the database account for the destination AnalyticDB for MySQL 3.0 cluster. For permission requirements, see Permissions required for database accounts.
	Database Password	The password that is used to access the database.

In the lower part of the page, click Test Connectivity and Proceed.
Note
Make sure that the CIDR blocks of DTS servers can be automatically or manually added to the security settings of the source and destination databases to allow access from DTS servers. For more information, see Add DTS server IP addresses to a whitelist.

Configure the objects to be synchronized.

In the Configure Objects step, configure the objects that you want to synchronize.

Configuration	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 cluster. The historical data is the basis for subsequent incremental synchronization.
DDL and DML Operations to Be Synchronized	Select the instance-level operations that you want to synchronize incrementally. Note To select operations for incremental synchronization on a per-table basis, right-click a table in the Selected Objects section and select the desired operations in the dialog box that appears.
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. Note If the source and destination databases contain tables with identical 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. Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to 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 instance fails. Proceed with caution.
Source Objects	In the Source Objects box, click the table that you want to sync, and then click to move the table to the Selected Objects box. Important You can select only one table to synchronize.
Selected Objects	To configure the name of an object to be synchronized in the destination database or specify an object that receives data in the destination database, right-click the object in the Selected Objects section. For more information, see Map object names. To remove a selected object, click the object in the Selected Objects section and then click the icon to move the object to the Source Objects section. Note 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. To specify WHERE conditions to filter data, right-click a table in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Specify filter conditions. To select SQL operations for incremental synchronization, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to synchronize.

Click Next: Advanced Settings to configure advanced settings.

Configuration	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data synchronization instances, purchase a dedicated cluster. For more information, see What is a DTS dedicated cluster.
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. Note 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.
Retry Time for Other Issues	The retry time range for other issues. For example, if the DDL or DML operations fail to be performed after the data synchronization task is started, DTS immediately retries the operations within the time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set this parameter to a value greater than 10. If the failed operations are successfully performed within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Important The value of the Retry Time for Other Issues parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Full Data Synchronization	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. Note You can configure this parameter 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.
Environment Tag	You can select an environment tag to identify the instance according to your business needs. In this example, you do not need to select a tag.
Configure ETL	Specifies whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.
Monitoring and Alerting	Specifies whether to configure alerting for the data synchronization instance. If the task fails or the synchronization latency exceeds the specified threshold, alert contacts will receive notifications. Valid values: No: does not enable alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see the "Configure monitoring and alerting when you create a DTS task" section of the Configure monitoring and alerting topic.

Click Next Step: Data Verification to configure data verification.
For more information about how to use the data verification feature, see Configure a data verification task.
Optional: After you complete the preceding configurations, click Next: Configure Database and Table Fields. Then, configure the Type, Primary Key Column, Distribution Key, and partition key information (Partition Key, Partitioning Rules, and Partition Lifecycle) for the tables to be synchronized in the destination database.
Note
- This step is available only if you select Schema Synchronization for Synchronization Types when you configure the task object. You can set Definition Status to All and make changes.
- For the Primary Key Column, you can select multiple columns to create a composite primary key. If you create a composite primary key, you must also select one or more columns from the Primary Key Column to act as the Distribution Key and Partition Key. For more information, see CREATE TABLE.

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.
Note
- 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 data synchronization task fails the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, rerun the precheck.
- 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.

Purchase the instance.

Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.

On the buy page, configure the Billing Method and Instance Class parameters for the data synchronization task. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Billing Method	Subscription: You pay for a subscription when you create a data synchronization 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. The pay-as-you-go billing method is suitable for short-term use. If you no longer require a pay-as-you-go data synchronization instance, you can release the instance to reduce costs.
	Resource Group Settings	The resource group to which the data synchronization instance belongs. Default value: default resource group. For more information, see What is Resource Management?
	Instance Class	DTS provides instance classes that vary in synchronization speed. You can select an instance class based on your business requirements. For more information, see Instance classes of data synchronization instances.
	Subscription Duration	If you select the subscription billing method, specify the subscription duration and the number of data synchronization instances that you want to create. The subscription duration can be one to nine months, one year, two years, three years, or five years. Note This parameter is available only if you select the Subscription billing method.

Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start. In the dialog box that appears, click OK.
You can view the progress of the task in the task list.