Synchronize data from a self-managed MySQL database to an Alibaba Cloud RDS for MySQL instance - Data Transmission Service

Prerequisites

You must connect the self-managed MySQL database to Alibaba Cloud. Add the CIDR blocks of DTS servers to the security settings of your database, such as security group rules, firewall rules, and whitelists, to grant access to DTS servers. For more information, see Preparations Overview.
Note
For more information about supported database versions, see Synchronization solution overview.
Create an account for the self-managed MySQL database and configure binary logging. For more information, see Create an account for a self-managed MySQL database and configure binary logging.
Create a destination RDS for MySQL instance. Ensure that the available storage space of the destination instance is larger than the storage space used by the self-managed MySQL database. For more information, see Create an RDS for MySQL instance.

Precautions

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	The tables to synchronize must have a primary key or a unique constraint, and the fields must be unique. Otherwise, duplicate data may appear in the destination database. If you synchronize at the table level and need to edit mappings (such as column name mapping), each synchronization task supports up to 1,000 tables. If you exceed this limit, the task fails with an error. To fix this, split the tables across multiple tasks or configure a full-database synchronization task. Binary logs: ApsaraDB RDS for MySQL enables binary logging by default. Ensure that the binlog_row_image parameter is set to full. Otherwise, the precheck fails and the synchronization task cannot start. For instructions, see Configure instance parameters. Important If your source instance is a self-managed MySQL database, enable binary logging and set binlog_format to row and binlog_row_image to full. If your self-managed MySQL database is a dual-primary cluster (where both nodes act as primary and secondary), enable the log_slave_updates parameter so DTS can capture all binary log events. For instructions, see Create an account and configure binary logging for a self-managed MySQL database. The local binary logs for an ApsaraDB RDS for MySQL instance must be retained for at least three days (seven days is recommended). For a self-managed MySQL database, retain local binary logs for at least seven days. Otherwise, DTS may fail to retrieve binary logs, causing the task to fail. In extreme cases, this may cause data inconsistency or data loss. Issues caused by binary log retention periods shorter than DTS requires are not covered under the DTS SLA. Note To configure the retention period for local binary logs on an ApsaraDB RDS for MySQL instance, see Automatically delete local logs. 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. Data generated by changes that do not write to binary logs—such as data restored from physical backups or created by cascade operations—is not synchronized to the destination database. Note If this occurs, remove the affected database or table from the synchronization objects. Then add it back. You can do this only if your business allows it. For more information, see Modify synchronization objects. If your source database is MySQL 8.0.23 or later and contains invisible hidden columns, DTS may not read those columns. This may cause data loss. Note Run the `ALTER TABLE <table_name> ALTER COLUMN <column_name> SET VISIBLE;` command to make the hidden column visible. For more information, see Invisible Columns. MySQL compatibility: When DTS synchronizes data from a MySQL-family source database, it relies on the standard MySQL protocol and Binlog format, and behaviors incompatible with standard MySQL are not supported. If your source database claims MySQL compatibility but behaves differently from MySQL (for example, when OceanBase is connected as a source in MySQL mode, the timestamp of the trailing rotate event in the Binlog is 0, which differs from MySQL), the DTS synchronization task may fail.
Other limits	Use the same version for the source and destination databases, or upgrade from a lower version to a higher version to ensure compatibility. Synchronizing from a higher version to a lower version may cause compatibility issues. If your source database uses online DDL operations in temporary table mode—including but not limited to multi-table merge scenarios—or adds function-based indexes to unique key columns, data loss or task failure may occur in the destination database. Resolvers defined by comment syntax do not support synchronous use. If a primary key or unique key conflict occurs while the task is running: 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. If your destination database is MySQL 8.0.23 or later and contains invisible hidden columns in the receiving columns, DTS may fail to locate the target column. This may cause task failure or data loss. Note Run the `ALTER TABLE <table_name> ALTER COLUMN <column_name> SET VISIBLE;` command to make the hidden column visible. For more information, see Invisible Columns. If you do not use DTS to synchronize table schemas, ensure field compatibility yourself. Otherwise, the task may fail or data may be lost. For example, if the source table uses the `text` data type and the destination column uses `varchar(255)`, large fields in the source table may be truncated. If your data includes four-byte characters—such as rare Chinese characters or emojis—the destination database and table must use the utf8mb4 charset. Note If you use DTS to synchronize table schemas, set the `character_set_server` parameter at the instance level in the destination database to utf8mb4. Assess the performance of both the source and destination databases before starting synchronization. Run synchronization during off-peak hours. Otherwise, full initialization consumes read and write resources on both databases and may increase database load. Full initialization runs INSERT operations concurrently. This fragments destination tables. After full initialization, the tablespace of the destination instance is larger than that of the source instance. If you synchronize one or more tables—not a full database—do not use tools like pt-online-schema-change to perform online DDL operations on the source tables. Otherwise, synchronization fails. You can use Data Management (DMS) to perform online DDL operations. For more information, see Online DDL without locking tables. Do not write data to the destination database except through DTS while synchronization is running. Otherwise, data inconsistency may occur between the source and destination databases. For example, if you use DMS to perform online DDL operations while other data is written to the destination database, data loss may occur. If a DDL operation fails in the destination database, the DTS task continues to run. Check the failed DDL in the task logs. For instructions, see View task logs. If you write columns with names that differ only in case to the same table in the destination MySQL database, unexpected results may occur because MySQL column names are case-insensitive. After data synchronization completes (the instance's Status is Completed), you should use the `ANALYZE TABLE <table_name>` command to confirm that all data is written to the target table. For example, after the HA failover mechanism is triggered in the target MySQL database, data might be written only to memory, which can cause data loss. If your ApsaraDB RDS for MySQL instance has Always-Encrypted enabled, full data synchronization is not supported. Note ApsaraDB RDS for MySQL instances with Transparent Data Encryption (TDE) enabled support schema synchronization, full data synchronization, and incremental data synchronization. To synchronize accounts from the source database, meet the prerequisites and review related considerations. For more information, see Migrate database accounts. 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.
Other considerations	For a self-managed MySQL source database: If a primary/secondary switchover occurs in the source database during synchronization, the task fails. DTS calculates latency by comparing the timestamp of the last synchronized record with the current time. If no DML operations run for a long time in the source database, latency reporting may become inaccurate. If latency appears too high, run a DML operation in the source database to update the latency. Note If you select a full database for synchronization, create a heartbeat table. Update or write to this table every second. DTS periodically runs the CREATE DATABASE IF NOT EXISTS `test` command in the source database to advance the binary log offset. If your source database is Amazon Aurora MySQL or another clustered MySQL instance, ensure the domain name or IP address used in the task configuration—and its DNS resolution—always points to a read/write (RW) node. Otherwise, synchronization may fail. For an ApsaraDB RDS for MySQL source database: Read-only instances—such as ApsaraDB RDS for MySQL 5.6 read-only instances—that do not record transaction logs cannot serve as source databases. DTS periodically runs the CREATE DATABASE IF NOT EXISTS `test` command in the source database to advance the binary log offset.

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 many-to-one synchronization
One-way cascade synchronization

SQL operations that can be synchronized

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 a single table and you rename it on the source instance during synchronization, the data of that table is not synchronized to the destination database. To avoid this issue, you can configure the task to synchronize the entire database that contains the table. Make sure that the database to which the table belongs both before and after the RENAME TABLE operation is included in the synchronization objects. TRUNCATE TABLE

Permissions required for database accounts

Database

Schema synchronization

Full synchronization

Incremental synchronization

Self-managed MySQL database

SELECT permission

Permission	Purpose
SELECT	Read data from objects to migrate, synchronize, or track
REPLICATION CLIENT	Read the binary log position
REPLICATION SLAVE	Read binary log events
SHOW VIEW	Read view definitions
CREATE on `.`	Create a database named `test` to advance the binary log position

RDS for MySQL instance

Read and write permissions

To create a database account and grant permissions:

Note

To synchronize the account information of the source database, the database account used to configure the task requires additional permissions. For more information, see Migrate database accounts.

For a self-managed MySQL database, see Create an account for a self-managed MySQL database and configure binary logging.
For an RDS for MySQL instance, see Create an account and Modify the permissions of an account.

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.

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.

Category	Configuration	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	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 MySQL.
	Access Method	Select a connection type based on the deployment location of the source database. In this example, Self-managed Database on ECS is selected. Note If the source is a self-managed database, you also need to complete the corresponding preparations.
	Instance Region	Select the region where the source MySQL database resides.
	Replicate Data Across Alibaba Cloud Accounts	This example involves synchronization within the same Alibaba Cloud account. Select No.
	ECS Instance ID	Select the ID of the ECS instance where the source MySQL database is located.
	Port	Enter the service port of the source MySQL database, which must be accessible over the public network. The default value is 3306.
	Database Account	Enter the account for the source MySQL database. For more information about the required permissions, see Permissions required for database accounts.
	Database Password	Enter the password for the specified database account.
	Encryption	Select Non-encrypted or SSL-encrypted as needed. If SSL encryption is not enabled for the self-managed MySQL database, select Non-encrypted. If SSL encryption is enabled for the self-managed MySQL database, select SSL-encrypted. You also need to upload a CA Certificate and enter the CA Certificate Password.
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 MySQL.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination RDS for MySQL instance resides.
	Replicate Data Across Alibaba Cloud Accounts	This example involves synchronization within the same Alibaba Cloud account. Select No.
	RDS Instance ID	Select the ID of the destination RDS for MySQL instance.
	Database Account	Enter the database account of the destination RDS for MySQL instance. For more information about the required permissions, see Permissions required for database accounts.
	Database Password	Enter the password for the specified database account.
	Encryption	Select Non-encrypted or SSL-encrypted as needed. If you set this to SSL-encrypted, you must enable SSL encryption for the RDS for MySQL instance beforehand. For more information, see Use a cloud certificate to quickly enable SSL link encryption.

After the configuration is complete, click Test Connectivity and Proceed at the bottom of the page. In the CIDR Blocks of DTS Servers dialog box, click Test Connectivity.
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.
Method to Migrate Triggers in Source Database	Select a method to synchronize triggers as required. You do not need to configure this parameter if the objects to be synchronized do not involve triggers. For more information, see Configure how to synchronize or migrate triggers. Note This parameter is available only if you select Schema Synchronization for Synchronization Types.
Enable Migration Assessment	This parameter assesses whether the schemas of the source and destination databases meet the requirements. This includes checks for index length, stored procedures, and dependent tables. You can select Yes or No as required. Note This parameter is available only if you select Schema Synchronization for Synchronization Types. If you select Yes, the precheck may take longer. You can view the Assessment Result during the precheck phase. The assessment result does not affect the precheck result.
Synchronization Topology	Select One-way 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 Object 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.
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, 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 If you use the object name mapping feature, other objects that depend on the renamed object may fail to synchronize. To select the SQL operations to be synchronized at the database or table level, right-click the object in the Selected Objects box and select the desired SQL operations in the dialog box that appears. 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 Filter task data with an SQL condition.

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?.
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	Specify whether to synchronize the account information of the source database as required. If you select Yes, you must also select the accounts to be synchronized and confirm their permissions.
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	You can select an environment tag to identify the instance as required. In this example, no selection is necessary.
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.
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.

Click Data Verification to configure a data verification task.
To use the data verification feature, see Configure data verification.

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 an 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.

FAQ

Q: After an instance starts running, can I change Whether to delete SQL operations on heartbeat tables of forward and reverse tasks?

A: No.