Synchronize data from an ApsaraDB RDS for MySQL instance to an ApsaraDB for SelectDB instance - Data Transmission Service

ApsaraDB for SelectDB can respond to queries on large amounts of data within sub-seconds, handle tens of thousands of concurrent point queries, and perform complex analysis with high throughput. Data Transmission Service (DTS) allows you to synchronize data from a self-managed MySQL database or an ApsaraDB RDS for MySQL instance to an ApsaraDB for SelectDB instance. This helps you analyze large amounts of data. This topic describes how to synchronize data from an ApsaraDB RDS for MySQL instance to an ApsaraDB for SelectDB instance by using DTS.

Prerequisites

The destination ApsaraDB for SelectDB instance is created. The available storage space of this instance is larger than the total size of data in the source ApsaraDB RDS for MySQL instance. For more information, see Create an instance.

Limits

Limit type	Description
Limits on the source database	The tables to be synchronized must have PRIMARY KEY or UNIQUE constraints, and all fields must be unique. Otherwise, the destination may contain duplicate data records. If you select tables as the objects to be synchronized and you need to modify the tables, such as renaming tables or columns, you can synchronize up to 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, we recommend that you split the tables and configure multiple tasks to synchronize the tables in batches or configure a task to synchronize the entire database. The following requirements for binary logs must be met: By default, the binary logging feature is enabled. The binlog_row_image parameter must be set to full. Otherwise, error messages are returned during precheck and the data synchronization task cannot be started. For more information, see Modify instance parameters. Important If the source database is a self-managed MySQL database, you must enable the binary logging feature and set the binlog_format parameter to row and the binlog_row_image parameter to full. If the source database is a self-managed MySQL database deployed in a dual-primary cluster, you must set the log_slave_updates parameter to ON. This ensures that DTS can obtain all binary logs. For more information, see Create an account for a self-managed MySQL database and configure binary logging. The binary logs of the source database must be stored for at least seven days. Otherwise, the data synchronization task may fail because DTS cannot obtain the binary logs. In exceptional circumstances, data inconsistency or loss may occur. Make sure that you configure the retention period of binary logs based on the preceding requirements. Otherwise, the service reliability or performance in the SLA of DTS may not be guaranteed. For more information about how to manage the binary log files of an ApsaraDB RDS for MySQL instance, see Manage binary log files. During schema synchronization and full data synchronization, do not execute DDL statements to change the schemas of databases or tables. Otherwise, the data synchronization task fails.
Other limits	You can synchronize data to only tables that use the Unique Key model in ApsaraDB for SelectDB instances. During data synchronization, do not create clusters in the destination ApsaraDB for SelectDB instance. Otherwise, the data synchronization task fails. ApsaraDB for SelectDB instances support only database names and table names that start with letters. If the name of a database or table that you want to synchronize does not start with a letter, you must use the object name mapping feature to rename the database or table. If the name of the object that you want to synchronize, such as a database, a table, or a column, contains Chinese characters, you must use the object name mapping feature to rename the object. For example, you can change the name from Chinese to English. Otherwise, the task may fail. During data synchronization, do not add backend nodes to the ApsaraDB for SelectDB database. Otherwise, the task fails. In ApsaraDB RDS for MySQL, M of the `VARCHAR(M)` data type represents the character length. In ApsaraDB for SelectDB, N of the `VARCHAR(N)` data type represents the byte length. If you do not use the schema synchronization feature provided by DTS, we recommend that you set the length of a VARCHAR field in ApsaraDB for SelectDB to four times the length of a VARCHAR field in ApsaraDB RDS for MySQL. 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 initial full data synchronization is complete, the 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 from the source database. 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 source database is an ApsaraDB RDS for MySQL instance for which the EncDB feature is enabled, full data synchronization cannot be performed.
Special cases	If the source database is a self-managed MySQL database, take note of the following items: If you perform a primary/secondary switchover on the source database when the data synchronization task is running, the task fails. DTS calculates synchronization latency based on the timestamp of the latest synchronized data in the destination database and the current timestamp in the source database. If no DML operation is performed on the source database for a long time, the synchronization latency may be inaccurate. If the latency of the data synchronization task is excessively high, you can perform a DML operation on the source database to update the latency. Note If you select an entire database as the object to be synchronized, you can create a heartbeat table. The heartbeat table is updated or receives data every second. DTS executes the CREATE DATABASE IF NOT EXISTS 'test' statement in the source database as scheduled to move forward the binary log file position. If the source database is an Apsara RDS for MySQL instance, take note of the following item: An ApsaraDB RDS for MySQL instance that does not record transaction logs, such as a read-only ApsaraDB RDS for MySQL 5.6 instance, cannot be used as the source database.

Billing

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

SQL operations that support incremental synchronization

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE
DDL	ADD COLUMN DROP COLUMN and DROP TABLE TRUNCATE TABLE

Permissions required for database accounts

Database	Required permission	References
Source ApsaraDB RDS for MySQL instance	The read and write permissions on the objects to be synchronized	Create an account and Modify the permissions of an account
Destination ApsaraDB for SelectDB instance	The USAGE_PRIV permission and the following read and write permissions: SELECT_PRIV, LOAD_PRIV, ALTER_PRIV, CREATE_PRIV, and DROP_PRIV.	Manage the permissions to access clusters and Manage the basic permissions of users

Note

If the source database account that you use is not created and granted permissions in the ApsaraDB RDS for MySQL console, make sure that the account has the REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions.

Procedure

Go to the Data Synchronization Tasks page.
1. Log on to the DMS console.
2. In the top navigation bar, move the pointer over DTS.
3. Choose DTS (DTS) > Data Synchronization.
Note
- The actual operation may vary depending on the mode and layout of DMS. For more information, see Simple mode and Customize the layout and style of the DMS console.
- You can also go to the Data Synchronization Tasks page of the new DTS console.
On the right side of Data Synchronization Tasks, select the region in which the data synchronization instance resides.
Note
If you use the new DTS console, select the region in which you want to create the data synchronization task in the top navigation bar.

Click Create Task. In the Create Data Synchronization Task wizard, configure the source and destination databases. The following table describes the parameters.

Section	Parameter	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 an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	The database instance that you want to use. You can choose whether to use an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the database.
	Database Type	The type of the source database. 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	Specifies whether data is synchronized across Alibaba Cloud accounts. In this example, No is selected.
	RDS Instance ID	The ID of the source ApsaraDB RDS for MySQL instance.
	Database Account	The database account of the source ApsaraDB RDS for MySQL instance. For information about the permissions that are required for the account, see the Permissions required for database accounts section of this topic.
	Database Password	The password that is used to access the database instance.
	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 an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	The database instance that you want to use. You can choose whether to use an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the database.
	Database Type	The type of the destination database. Select SelectDB.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination ApsaraDB for SelectDB instance resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether data is synchronized across Alibaba Cloud accounts. In this example, No is selected.
	Instance ID	The ID of the destination ApsaraDB for SelectDB instance.
	Database Account	The database account of the destination ApsaraDB for SelectDB instance. For information about the permissions that are required for the account, see the Permissions required for database accounts section of this topic.
	Database Password	The password that is used to access the database instance.

In the lower part of the page, click Test Connectivity and Proceed.
If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance, and you must make sure that the ECS instance can access the database. If the database is deployed on multiple ECS instances, you must manually add the CIDR blocks of DTS servers to the security group rules of each ECS instance. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the whitelist of the database to allow DTS to access the database. For more information, see Add the CIDR blocks of DTS servers.
Warning
If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database or instance, or to the ECS security group rules, security risks may arise. Therefore, before you use DTS to synchronize data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

Configure the objects to be synchronized and advanced settings. The following table describes the parameters.

Parameter	Description
Synchronization Types	The synchronization types. By default, Incremental Data Synchronization is selected. You must also select Schema Synchronization and Full Data Synchronization. After the precheck is complete, DTS synchronizes the historical data of the selected objects from the source database to the destination cluster. The historical data is the basis for subsequent incremental synchronization. Important After you synchronize data from an ApsaraDB RDS for MySQL instance to an ApsaraDB for SelectDB instance, the data types are converted. If you do not select Schema Synchronization for the Synchronization Types parameter, you must create tables that use the Unique Key model in the destination ApsaraDB for SelectDB instance before data synchronization. The schemas of the destination tables must be compatible with the synchronized data. For more information, see the Data type mappings section of this topic and Data models.
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 migration, DTS does not migrate 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 task 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 databases, tables, or columns 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 SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to synchronize. For more information, see the SQL operations that support incremental synchronization section of this topic. To specify WHERE conditions to filter data, right-click a table in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Specify filter conditions. If you use the object name mapping feature to rename an object, other objects that are dependent on the object may fail to be synchronized.

Click Next: Advanced Settings to configure advanced settings.

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules tasks to shared clusters. You do not need to configure this parameter. If you want to improve the stability of data migration tasks, 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 Migration	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 This parameter is displayed 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	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements. In this example, no environment tag is selected.
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. Yes: does not write SQL operations on heartbeat tables. In this case, 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 task. 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 contacts. For more information, see Configure monitoring and alerting when you create a DTS task.

Optional. In the lower part of the page, click Next: Configure Database and Table Fields. In the dialog box that appears, specify Primary Key Column, Distribution Key, and Engine parameters for the tables that you want to synchronize. The parameter values apply after the tables are synchronized to the destination ApsaraDB for SelectDB instance.
Note
- This step is available only if you select Schema Synchronization for the Synchronization Types parameter. You can set Definition Status to All and modify the database and table fields.
- You can select multiple columns for the Primary Key Column parameter from the drop-down list. One or more columns specified for the Primary Key Column parameter can be selected for the Distribution Key parameter. You can select only unique for the Engine parameter.
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.
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 instance. 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 the 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.

Data type mappings

Category	Data type in ApsaraDB RDS for MySQL	Data type in ApsaraDB for SelectDB
Numeric	TINYINT	TINYINT
	TINYINT UNSIGNED	SMALLINT
	SMALLINT	SMALLINT
	SMALLINT UNSIGNED	INT
	MEDIUMINT	INT
	MEDIUMINT UNSIGNED	BIGINT
	INT	INT
	INT UNSIGNED	BIGINT
	BIGINT	BIGINT
	BIGINT UNSIGNED	LARGEINT
	BIT(M)	INT
	Decimal	Decimal Note ZEROFILL is not supported.
	Numeric	Decimal
	Float	Float
	Double	DOUBLE
	BOOL BOOLEAN	BOOLEAN
DATE AND TIME	DATE	DATEV2
	DATETIME[(fsp)]	DATETIMEV2
	Timestamp[(fsp)]	DATETIMEV2
	Time[(fsp)]	VARCHAR
	YEAR[(4)]	INT
STRING	CHAR VARCHAR	VARCHAR Important To avoid data loss, data of the CHAR and VARCHAR(n) types is converted to VARCHAR(4*n) after the data is synchronized to the destination ApsaraDB for SelectDB instance. If you do not specify the length of data, the default value VARCHAR(65533) is used. Data with a length of more than 65,533 characters is converted to the STRING type after it is synchronized to the destination ApsaraDB for SelectDB instance.
	BINARY VARBINARY	STRING
	TINYTEXT TEXT MEDIUMTEXT LONGTEXT	STRING
	TINYBLOB BLOB MEDIUMBOLB LONGBLOB	STRING
	ENUM	STRING
	SET	STRING
	JSON	STRING