Synchronize data from MySQL to PolarDB-X 1.0 - Data Transmission Service

This topic describes how to use Data Transmission Service (DTS) to synchronize data from an ApsaraDB RDS for MySQL instance to a PolarDB-X 1.0 instance.

Prerequisites

Ensure that the character set of the data to be synchronized from the source ApsaraDB RDS for MySQL instance is not utf8mb3.
You have created a destination PolarDB-X 1.0 instance. The available storage space of this instance must be larger than the storage space that is used by the source ApsaraDB RDS for MySQL instance. For more information, see Create a PolarDB-X 1.0 instance.
Note
When you create the instance, you must set the storage class to RDS MySQL.
A database and tables have been created in the destination PolarDB-X 1.0 instance to receive data. For more information, see Create a database and Perform basic SQL operations.

Usage notes

Category	Description
Limits on the source database	The server on which the source database is deployed must have sufficient outbound bandwidth. Otherwise, the data synchronization speed is affected. The tables to be synchronized must have a primary key or a UNIQUE constraint, and the fields must be unique. Otherwise, duplicate data may exist in the destination database. You can select only tables as the objects to be synchronized. If you want to edit the tables to be synchronized, such as by mapping table or column names, you can synchronize a maximum of 1,000 tables in a single data synchronization task. If you run a task to synchronize more than 1,000 tables, a request error occurs. In this case, split the tables to be synchronized and configure multiple tasks to synchronize them in batches. Binary logs: Binary logging is enabled for ApsaraDB RDS for MySQL instances by default. You must make sure that the `binlog_row_image` parameter is set to `full`. Otherwise, a precheck error is reported and the data synchronization task cannot start. For more information about how to set parameters, see Set instance parameters. Important If the source instance is a self-managed MySQL database, you must enable binary logging and set the `binlog_format` parameter to `row` and the `binlog_row_image` parameter to `full`. If the source self-managed MySQL database is in a primary/primary architecture where the two databases are the primary and secondary of each other, you must enable the `log_slave_updates` parameter. This ensures that DTS can obtain all binary logs. For more information, see Create a database account for a self-managed MySQL database and configure binary logging. The local binary logs of an ApsaraDB RDS for MySQL instance must be retained for at least 3 days. We recommend that you retain them for 7 days. The local binary logs of a self-managed MySQL database must be retained for at least 7 days. Otherwise, the DTS task may fail because DTS cannot obtain the binary logs. In extreme cases, data may be inconsistent or lost. Issues that are 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 local binary logs of an ApsaraDB RDS for MySQL instance, see Automatically delete local logs. The storage class of the PolarDB-X 1.0 instance must be RDS MySQL, which is a private custom RDS. PolarDB MySQL is not supported. During full data synchronization, do not perform DDL operations to change the schemas of databases or tables. Otherwise, the data synchronization task fails. Note During the full synchronization phase, DTS queries the source database. This generates metadata locks, which may block the execution of DDL operations on the source database. During the runtime of the DTS instance, data changes from operations that are not recorded in binary logs are not synchronized to the destination database. Examples of such operations include data recovery using physical backups and cascade operations. Note If this occurs, you can remove the database or table from the synchronization objects and then add it back. This is allowed if your business permits. For more information, see Modify synchronization objects. If the source database is MySQL 8.0.23 or later and the data to be synchronized contains invisible columns, data may be lost because DTS cannot obtain the data of these columns. Note You can run the `ALTER TABLE <table_name> ALTER COLUMN <column_name> SET VISIBLE;` command to make the invisible columns visible. For more information, see Invisible Columns. Tables without a primary key automatically generate an invisible primary key. You must also make this invisible primary key visible. For more information, see Generated Invisible Primary Keys.
Other limits	Schema synchronization is not supported. Before you configure a data synchronization task, you must create databases and tables in the destination PolarDB-X 1.0 instance based on the databases and tables that you want to synchronize. You cannot select data whose character set is utf8mb3 for incremental synchronization. Otherwise, the data synchronization task fails. If you perform online DDL operations that use temporary tables in the source database, such as merging multiple tables, data may be lost in the destination database or the DTS instance may fail. Before you synchronize data, evaluate the impact of data synchronization on the performance of the source and destination databases. We recommend that you synchronize data during off-peak hours. During initial full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. During initial full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination database. After the initial full data synchronization is complete, the size of the used tablespace of the destination database is larger than that of the source database. During data synchronization, do not use tools such as pt-online-schema-change to perform online DDL operations on the objects to be synchronized. Otherwise, the data synchronization task fails. Data inconsistency between the source and destination databases may occur if data from other sources is written to the destination database during data synchronization. If the always-confidential (EncDB) feature is enabled for the ApsaraDB RDS for MySQL instance, full data synchronization is not supported. Note ApsaraDB RDS for MySQL instances for which Transparent Data Encryption (TDE) is enabled support schema synchronization, full data synchronization, and incremental data synchronization. If an instance fails, DTS helpdesk will try to recover the instance within 8 hours. During the recovery process, operations such as restarting the instance and adjusting parameters may be performed. Note When parameters are adjusted, only the parameters of the DTS instance are modified. The parameters of the database are not modified. The parameters that may be modified include but are not limited to those described in Modify instance parameters.
Special cases	If the source database is a self-managed MySQL database: If a primary/secondary failover occurs in the source database during synchronization, the sync task fails. The latency of DTS is calculated based on the difference between the current timestamp and the timestamp of the last data record synchronized to the destination database. If no DML operations are performed on the source database for a long time, the latency information may be inaccurate. If the displayed latency is too high, you can perform a DML operation on the source database to update the latency information. Note If you choose to synchronize the entire database, you can also create a heartbeat table. The heartbeat table is updated or written to every second. DTS periodically runs the CREATE DATABASE IF NOT EXISTS `test` command on the source database to advance the binary log offset. If the source database is an Amazon Aurora MySQL instance or another MySQL instance in cluster mode, make sure that the domain name or IP address configured for the task and its resolution result always point to the read/write (RW) node. Otherwise, the sync task may not run properly. If the source database is an ApsaraDB RDS for MySQL instance: ApsaraDB RDS for MySQL instances that do not record transaction logs, such as read-only instances of ApsaraDB RDS for MySQL 5.6, cannot be used as a source database. DTS periodically runs the CREATE DATABASE IF NOT EXISTS `test` command on the source database to advance the binary log offset.

Billing

Synchronization type	Link Configuration Fees
Full data synchronization	Free of charge.
Incremental data synchronization	Charged. For more information, see Billing overview.

SQL operations that support incremental synchronization

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE

Permissions required for database accounts

Database	Required permissions	Creation and authorization methods
Source ApsaraDB RDS for MySQL	Read and write permissions	Create an account and Modify the permissions of an account.
Destination PolarDB-X 1.0	Read and write permissions	Manage database accounts.

Note

If the source database account that you use was not created and authorized in the ApsaraDB RDS for MySQL console, ensure that the account has the REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions.

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 MySQL.
	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source ApsaraDB RDS for MySQL instance resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database of the current Alibaba Cloud account is used. Select No.
	RDS Instance ID	Select the ID of the source ApsaraDB RDS for MySQL instance.
	Database Account	Enter the database account of the source ApsaraDB RDS for MySQL instance. For information about the required permissions, see Permissions required for database accounts.
	Database Password	The password that is used to access the database.
	Encryption	Specifies whether to encrypt the connection to the database. You can select Non-encrypted or SSL-encrypted based on your business requirements. If you want to set this parameter to SSL-encrypted, you must enable SSL encryption for the ApsaraDB RDS for MySQL instance before you configure the DTS task. For more information, see Use a cloud certificate to enable SSL encryption.
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 PolarDB-X 1.0.
	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination PolarDB-X 1.0 instance resides.
	Instance ID	Select the ID of the destination PolarDB-X 1.0 instance.
	Database Account	Enter the database account of the destination PolarDB-X 1.0 instance. For information about the required permissions, see Permissions required for database accounts.
	Database Password	The password that is used to access the database.

Click Test Connectivity and Proceed in the lower part of the page.
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.
- If the source or destination database is a self-managed database and its Access Method is not set to Alibaba Cloud Instance, click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

Configure the objects to be synchronized.

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

Configuration	Description
Synchronization Types	By default, Incremental Data Synchronization is selected. You can select only Full Data Synchronization. You cannot select Schema Synchronization. After the precheck is complete, DTS synchronizes the historical data of the selected objects from the source database to the destination database. The historical data is the basis for subsequent incremental synchronization.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that have the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck, and the data synchronization task cannot be started. 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.
Capitalization of Object Names in Destination Instance	The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to ensure that the capitalization of object names is consistent with that in the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.
Source Objects	Select one or more objects from the Source Objects section and click the icon to add the objects to the Selected Objects section. Note You can select tables as the objects to be synchronized.
Selected Objects	To rename an object that you want to synchronize to the destination instance, right-click the object in the Selected Objects section. For more information, see the "Map the name of a single object" section of the Map object names topic. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see the "Map multiple object names at a time" section of the Map object names topic. Note To select the DML operations for incremental synchronization, right-click an object in the Selected Objects box. In the dialog box that appears, select the DML operations that you want to synchronize. For more information about the supported operations, see SQL operations that support incremental synchronization. To specify WHERE conditions to filter data, right-click a table in the Selected Objects box. In the dialog box that appears, specify the filter conditions. For more information about how to set the conditions, see Set filter conditions. If you use the object name mapping feature, other objects that depend on the mapped object may fail to be synchronized.

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 based on your business needs. In this example, you do not need to select a tag.
Whether to delete SQL operations on heartbeat tables of forward and reverse tasks	Specifies whether to write SQL operations on heartbeat tables to the source database while the DTS instance is running. Valid values: Yes: does not write SQL operations on heartbeat tables. In this case, a latency of the DTS instance may be displayed. No: writes SQL operations on heartbeat tables. In this case, features such as physical backup and cloning of the source database may be affected.
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.

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.