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    PolarDB:Synchronize data from a PolarDB for MySQL cluster to an ApsaraDB RDS for MySQL instance

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    PolarDB:Synchronize data from a PolarDB for MySQL cluster to an ApsaraDB RDS for MySQL instance

    Last Updated:Aug 31, 2026

    Data Transmission Service (DTS) allows you to synchronize data from a PolarDB for MySQL cluster to a MySQL database, including self-managed MySQL databases and ApsaraDB RDS for MySQL instances.

    Supported destination databases

    PolarDB for MySQL cluster to MySQL. The following types of destination databases are supported. This topic uses an ApsaraDB RDS for MySQL instance as an example to describe the configuration procedure. The configuration procedures for other types of destination databases are similar.

    • ApsaraDB RDS for MySQL instance

    • Self-managed database that is hosted on Elastic Compute Service (ECS)

    • Self-managed database that is connected over Express Connect, VPN Gateway, or Smart Access Gateway

    • Self-managed database that is connected over Database Gateway

    • Self-managed database that is connected over Cloud Enterprise Network (CEN)

    Prerequisites

    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 be synchronized must have a primary key or a UNIQUE constraint, and all fields must be unique. Otherwise, duplicate data may appear in the destination database.

      Note

      If a table to be synchronized in a two-way synchronization instance does not have a primary key or UNIQUE constraint, you can enable the Exactly-Once write feature. For more information, see Synchronize tables without primary keys or unique constraints.

    • If you synchronize data at the table level and need to edit tables (for example, mapping column names), a single synchronization task supports up to 1,000 tables. If you exceed this limit, an error is reported when you submit the task. To resolve this, split the tables into multiple synchronization tasks or synchronize the entire database.

    • Binary logs:

      • You must enable binary logging and set the loose_polar_log_bin parameter to ON. Otherwise, an error is reported during the precheck and the DTS instance fails to start. For more information about how to enable binary logging and modify parameters, see Enable binary logging and Set cluster and node parameters.

        Note

        Enabling binary logging for a PolarDB for MySQL cluster consumes storage space and incurs fees.

      • Binary logs of the PolarDB for MySQL cluster must be retained for at least 3 days. We recommend retaining them for 7 days. Otherwise, the DTS 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 shorter than the required period are not covered by the DTS Service-Level Agreement (SLA).

        Note

        For more information about how to set the retention period for binary logs of a PolarDB for MySQL cluster, see Modify the retention period.

    • 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

    • You cannot synchronize data from a read-only node of the source PolarDB for MySQL cluster.

    • You cannot synchronize OSS foreign tables from the source PolarDB for MySQL cluster.

    • Synchronization of INDEX and PARTITION is not supported.

    • Primary/secondary failover of the database instance is not supported during initial full data synchronization. If a failover occurs, reconfigure the synchronization task.

    • 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 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.

    • Before you synchronize data, evaluate the performance of the source and destination databases. We recommend synchronizing data during off-peak hours. Otherwise, initial full data synchronization consumes read and write resources on both databases, which may increase the database load.

    • Initial full data synchronization runs concurrent INSERT operations, which causes fragmentation in the destination database tables. As a result, the tablespace of the destination instance is larger than that of the source instance after initial full data synchronization.

    • For table-level data synchronization, do not use tools such as pt-online-schema-change to perform online DDL operations on the synchronization objects in the source database. Otherwise, the synchronization fails.

    • For table-level data synchronization, if no data other than the data from DTS is written to the destination database, you can use Data Management (DMS) to perform online DDL operations. For more information, see Change schemas without locking tables.

    • During DTS synchronization, do not write data other than DTS data to the destination database. Otherwise, data inconsistency between the source and destination databases may occur. For example, if you use DMS to perform online DDL operations while other data is being written to the destination database, data may be lost.

    • If a DDL operation fails to be written to the destination database, the DTS task continues to run. Check the task logs for the failed DDL operation. For more information about how to view task logs, 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.

    • A two-way synchronization task includes forward and reverse synchronization tasks. When you configure or reset the task, if the destination object of one task matches the synchronization object of the other task:

      • Allow only one task to synchronize full and incremental data. The other task supports only incremental synchronization.

      • Data from the source of the current task synchronizes only to the destination of the current task. It does not serve as source data for the other task.

    • 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 notes

    DTS periodically runs the CREATE DATABASE IF NOT EXISTS `test` command on 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 architectures

    • One-way one-to-many synchronization

    • One-way cascade synchronization

    • Two-way cascade synchronization

    • One-way many-to-one synchronization

    • Two-way one-to-one synchronization

      For more information about each synchronization architecture and the related considerations, see Data Synchronization Topologies.

    Supported SQL operations for synchronization

    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

    Required permissions for database accounts

    Database

    Required permissions

    How to create and authorize accounts

    PolarDB for MySQL cluster

    Read permissions on the objects to be synchronized

    Create and manage database accounts

    ApsaraDB RDS for MySQL instance

    Read and write permissions on the destination database

    Create an account

    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.

    Procedure

    1. 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.

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

    3. 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

      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

      • 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 for MySQL.

      Connection Type

      Select Cloud Instance.

      Instance Region

      Select the region where the source PolarDB for MySQL cluster resides.

      Replicate Data Across Alibaba Cloud Accounts

      For this example, select No, as the database instance belongs to the current Alibaba Cloud account.

      PolarDB Cluster ID

      Select the source PolarDB for MySQL cluster ID.

      Database Account

      Enter the database account of the source PolarDB for MySQL cluster. For information about the required permissions, see Required permissions for database accounts.

      Database Password

      Enter the password for the specified database account.

      Encryption

      Select an option based on your requirements. For more information, see Configure SSL encryption.

      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.

      Connection Type

      Select Cloud Instance.

      Instance Region

      Select the region where the destination ApsaraDB RDS for MySQL instance resides.

      Replicate Data Across Alibaba Cloud Accounts

      For this example, select No, as the database instance belongs to the current Alibaba Cloud account.

      RDS Instance ID

      Select the destination ApsaraDB RDS for MySQL instance ID.

      Database Account

      Enter the database account of the destination ApsaraDB RDS for MySQL instance. For information about the required permissions, see Required permissions for database accounts.

      Database Password

      Enter the password for the specified database account.

      Connection Method

      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.

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      Connection Method

      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 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 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 how 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 parameter. For more information, see Configure trigger synchronization or migration.

      Note

      This parameter can be configured only when Synchronization Types includes Schema Synchronization.

      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 向右 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 filter data by condition, right-click the table to be synchronized in the Selected Objects section, and then set the filter conditions in the dialog box that appears. For more information, see Filter task data with an SQL condition.

      • To select SQL operations to be synchronized at the database or table level, right-click the object to be synchronized in the Selected Objects section, and then select the required SQL operations in the dialog box that appears. For information about supported operations, see Supported SQL operations for synchronization.

      • 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.

      Parameter

      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

      Select whether to synchronize account information from the source database based on your business requirements. If you select Yes, you also need to select the accounts to be synchronized and confirm the account 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

      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 select one.

      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:

      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.

    1. Click Next: Data Validation to configure a data validation task.

    2. If you want to use the data validation feature, see Configure data validation for configuration instructions.

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    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 select one.

    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:

    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.

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    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.

  • 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 the instance.

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

    2. On the Purchase page, select the billing method and link specification for the data synchronization instance. The following table describes these parameters in detail.

      3. Category

      Parameter

      Description

      New Instance Class

      Billing Method

      • Subscription: You pay when you create the instance. This is suitable for long-term needs and is more cost-effective than pay-as-you-go. The longer the subscription duration, the higher the discount.

      • Pay-as-you-go: You are charged on an hourly basis. This is suitable for short-term needs. You can release the instance immediately after use to save costs.

      Resource Group Configuration

      The resource group to which the instance belongs. The default is default resource group. For more information, see What is Resource Management?.

      Link Specification

      DTS provides sync specifications with different performance levels. The sync link specification affects the synchronization rate. You can choose a specification based on your business scenario. For more information, see Data synchronization link specifications.

      Subscription Duration

      In subscription mode, select the duration and quantity for the subscription instance. You can choose a monthly subscription from 1 to 9 months, or a yearly subscription of 1, 2, 3, or 5 years.

      Note

      This option is only available when the billing method is Subscription.

    3. After you complete the configuration, read and select Data Transmission Service (Pay-as-you-go) Service Terms.

    4. Click Buy and Start. In the OK dialog box, click OK.

    5. You can view the task progress on the Data Synchronization page.

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