Synchronization between ApsaraDB RDS for MariaDB instances-Data Transmission Service(DTS)-阿里云帮助中心

Prerequisites

Create a destination ApsaraDB RDS for MariaDB instance. For more information, see Create an ApsaraDB RDS for MariaDB instance.
The destination ApsaraDB RDS for MariaDB instance must have more available storage space than the source ApsaraDB RDS for MariaDB instance uses.

Usage 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 limits	Synchronized tables must have a `PRIMARY KEY` or a unique constraint with unique fields. Otherwise, the destination database may contain duplicate data. If you select specific tables and edit their mappings (such as for table or column names), a single data synchronization task supports a maximum of 1,000 tables. Exceeding this limit causes an error upon submission. To resolve this, split the tables into multiple tasks or configure the task to synchronize the entire database. Binary log requirements: Binlog is enabled by default in ApsaraDB RDS for MariaDB. You must ensure that the value of the `binlog_row_image` parameter is set to `full`. Otherwise, an error is reported during the precheck, and the data synchronization task cannot be started successfully. For an incremental data synchronization task, the binary log of the source database must be retained for at least 24 hours. For a task that includes both full data synchronization and incremental data synchronization, the binary log must be retained for at least 7 days. You can change the retention period back to 24 hours after the full data synchronization is complete. If the binary log retention period is insufficient, DTS may fail to obtain the logs, causing the task to fail. In extreme cases, this can lead to data inconsistency or loss. Issues caused by an insufficient binary log retention period are not covered by the DTS Service Level Agreement (SLA). 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.
Other limits	Ensure that both the source columns to be synchronized and the destination columns do not contain invisible columns. Otherwise, the DTS instance may fail to run or data may be lost. For compatibility, we recommend that the source and destination databases have the same version, or that you synchronize from an earlier version to a later one. Synchronizing from a later to an earlier version may cause compatibility issues. Before synchronizing, evaluate the performance of the source and destination databases. We recommend performing data synchronization during off-peak hours because full data initialization consumes read and write resources on both databases, increasing their workloads. Full data initialization uses concurrent INSERT operations, which can fragment tables in the destination database. Consequently, the destination instance's tablespace will be larger than the source's after initialization. When synchronizing specific tables instead of an entire database, do not use tools like `pt-online-schema-change` for online DDL changes on those tables in the source database, as this will cause the task to fail. You can use Data Management Service (DMS) to perform online DDL changes. For more information, see Perform lock-free DDL operations. During DTS synchronization, do not use other tools to write data to the destination database, as this will cause data inconsistency. For example, writing data with other tools while using DMS for online DDL changes can lead to data loss in the destination database. If a DDL operation fails to write to the destination database, the DTS task continues to run. You must check the task logs for the failed DDL statement. For more information about how to view task logs, see View task logs. 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.

Supported synchronization topologies

One-way one-to-one synchronization
One-way one-to-many synchronization
One-way cascade synchronization
One-way many-to-one synchronization
Two-way one-to-one synchronization

For more information about the synchronization topologies and their usage notes, see Data synchronization topologies.

Supported SQL operations

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE
DDL	ALTER TABLE, ALTER VIEW CREATE FUNCTION, CREATE INDEX, CREATE PROCEDURE, CREATE TABLE, CREATE VIEW DROP INDEX, DROP TABLE RENAME TABLE Important The RENAME TABLE operation may cause data inconsistency. For example, if the synchronization object is only a specific table and you rename the table in the source instance during synchronization, the data of the table is not synchronized to the destination database. To prevent this issue, select the entire database to which the table belongs as the synchronization object when you configure the data synchronization task. Make sure that the databases to which the table belongs before and after the RENAME TABLE operation are both included in the synchronization object. TRUNCATE TABLE

Database account permissions

Database	Permissions	Account setup
Source ApsaraDB RDS for MariaDB	Read and write permissions	Create an account and Modify the permissions of an account or reset the password.
Destination ApsaraDB RDS for MariaDB	Read and write permissions

Note

If the source database account was not created in the ApsaraDB RDS for MariaDB console, you must manually grant it the REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions.

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

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 Existing Connection	In this example, no database instance is selected. Configure the following database information.
	Database Type	Select MariaDB.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source ApsaraDB RDS for MariaDB instance resides.
	Cross-account	In this example, data is synchronized within the same Alibaba Cloud account. Select No.
	Instance ID	Select the instance ID of the source ApsaraDB RDS for MariaDB instance.
	Database Account	Enter the database account for the source ApsaraDB RDS for MariaDB instance. This account must have read permissions on the objects to be synchronized.
	Database Password	Enter the password for the specified database account.
	Connection method	Select Non-encrypted.
Destination Database	Select Existing Connection	In this example, no database instance is selected. Configure the following database information.
	Database Type	Select MariaDB.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination ApsaraDB RDS for MariaDB instance resides.
	RDS Instance ID	Select the instance ID of the destination ApsaraDB RDS for MariaDB instance.
	Database Account	Enter the database account for the destination ApsaraDB RDS for MariaDB instance. This account must have read and write permissions on the destination database.
	Database Password	Enter the password for the specified database account.
	Connection method	Select Non-encrypted.

After completing the configuration, click Test Connectivity and Proceed at the bottom of the page.
Note
- Ensure that you add the CIDR blocks of the DTS servers (either automatically or manually) to the security settings of both the source and destination databases to allow access. For more information, see Add the IP address whitelist of DTS servers.
- If the source or destination is a self-managed database (i.e., the Access Method is not Alibaba Cloud Instance), you must also click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

Configure the task objects.

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

Parameter	Description
Synchronization Type	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 objects to be synchronized do not involve triggers, you do not need to configure this setting. For more information, see Configure how to synchronize or migrate triggers. Note This setting is available only if Synchronization Types includes Schema Synchronization.
Processing Mode for Existing Destination 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.
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 to synchronize at the database or table level, right-click the object in the Selected Objects box and select the desired SQL operations from the dialog box that appears. To filter data by using WHERE conditions, right-click the table in the Selected Objects box and set the filter conditions in the dialog box that appears. For instructions, see Set filter conditions. If you use the object name mapping feature, other objects that depend on the renamed object may fail to synchronize.

Click Next: Advanced Settings.

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules tasks on a shared cluster. You do not need to select one. If you want more stable tasks, you can purchase a dedicated cluster to run DTS migration tasks.
Retry Interval After Source or Destination Database Connection Failure	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 Migration	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	You can select an environment tag to identify the instance based on your business requirements. In this example, you do not need to configure this setting.
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.

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.