Use DTS to import data to ApsaraDB for SelectDB - ApsaraDB for SelectDB

Data Transmission Service (DTS) supports full data and incremental data migrations. You can use DTS to migrate data from MySQL databases, such as self-managed MySQL databases, ApsaraDB RDS for MySQL instances, and PolarDB for MySQL clusters, to ApsaraDB for SelectDB instances. This way, you can query large amounts of data and obtain query results in sub-seconds, perform tens of thousands of concurrent point queries, and perform complex data analysis with high throughput on ApsaraDB for SelectDB instances.

Limits

Category	Description
Limits on the source database	The tables to be synchronized must have primary keys or UNIQUE constraints, and all fields must be unique. Otherwise, you must perform the following operations: In the Configure Objects and Advanced Settings step, select Schema Synchronization. In the Configure Database and Table Fields step, use the Unique key model for the tables and manually configure the primary key columns of the tables. The following requirements for binary logs must be met: By default, the binary logging feature is enabled. The binlog_row_image parameter is set to full. Otherwise, error messages are returned during the 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 is stored for at least seven days. Otherwise, DTS may fail to obtain the binary logs and the task may fail. 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 level agreement (SLA) of DTS does not guarantee service reliability or performance. For more information about how to manage the binary log files of an ApsaraDB RDS for MySQL instance, see Manage binary log files.
Other limits	You can synchronize data only to tables that use the Unique key model in ApsaraDB for SelectDB instances. 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 data synchronization, do not use tools such as pt-online-schema-change to perform online DDL operations on the objects to be synchronized in the source database. Otherwise, data synchronization may fail. During data synchronization, we recommend that you use only DTS to write data to the destination database. This prevents data inconsistency between the source and destination databases.
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 the 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 an extended period of time, the synchronization latency may be inaccurate. If the synchronization latency is too 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: The source Apsara RDS for MySQL instance cannot be a read-only ApsaraDB RDS for MySQL instance that does not record transaction logs, such as an ApsaraDB RDS for MySQL V5.6 instance.

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 can be incrementally synchronized

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
Source ApsaraDB RDS for MySQL instance	The read and write permissions on the objects to be synchronized
Destination ApsaraDB for SelectDB instance	The USAGE_PRIV permission on the destination ApsaraDB for SelectDB instance and the following read and write permissions on the destination database: SELECT_PRIV, LOAD_PRIV, ALTER_PRIV, CREATE_PRIV, and DROP_PRIV.

Note

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

Procedure

Log on to the ApsaraDB for SelectDB console.
In the top navigation bar, select the region in which the ApsaraDB for SelectDB instance resides.
In the left-side navigation pane, click Instances. On the Instances page, find the instance to which you want to import data and click its ID. The Instance Details page appears.
In the left-side pane, click Data Migration and Synchronization. On the page that appears, click the Data Synchronization tab.
Note
In most cases, a data synchronization task of DTS involves the migration of existing data and real-time synchronization of incremental data. Data migration is generally used to migrate existing historical data. For more information about the differences between data synchronization and data migration, see the FAQ section of this topic.
Click Create Data Synchronization Task to configure the information about the source and destination databases.

Section	Parameter	Description
N/A	Task Name	The name of the task. DTS automatically assigns a name to the task. 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	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	The region in which the source ApsaraDB RDS for MySQL instance resides.
	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 of the database account.
	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 select SSL-encrypted, you must enable SSL encryption for the ApsaraDB RDS for MySQL instance before you configure the data synchronization task. For more information, see Configure the SSL encryption feature.
Destination 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.
	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 the "Synchronize data from an ApsaraDB RDS for MySQL instance to an ApsaraDB for SelectDB instance" topic.
	Database Password	The password of the database account.

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 for SelectDB, ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the IP address whitelist of the instance.

Warning

If the public CIDR blocks of DTS servers are automatically or manually added to the whitelist of a database instance or to the security group rules of an Elastic Compute Service (ECS) instance, security risks may arise. Therefore, before you use DTS to migrate 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 security group rules and forbidding unauthorized CIDR blocks, or connecting the database instance 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	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 When you synchronize data from a MySQL database to an ApsaraDB for SelectDB instance, type conversion occurs . If you do not select Schema Synchronization, you must create tables that use the Unique key model with corresponding schemas in the destination ApsaraDB for SelectDB instance in advance. For more information, see the Data type mappings section of the "Synchronize data from an ApsaraDB RDS for MySQL instance to an ApsaraDB for SelectDB instance" 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 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 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. This indicates that database names and table names in the destination instance are in lowercase. The capitalization of column names in the destination instance is the same as that in the source database. You can also select Consistent with the source database or Consistent with the default policy of the 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. You can select databases, tables, or columns as the objects to be synchronized. Important If you select databases as the objects to be synchronized, DTS does not synchronize new data tables. If data tables are added to the source database during data synchronization, select tables as the objects to be synchronized. To modify the objects to be synchronized in a data synchronization task, find the data synchronization task on the Data Synchronization page in the DTS console and click Reselect Objects in the Actions column. If you select tables as the objects to be synchronized and you need to edit 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 configure multiple tasks to synchronize the tables in batches or configure a task to synchronize the entire database.
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 synchronize SQL operations that are 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 can be incrementally synchronized section of the "Synchronize data from an ApsaraDB RDS for MySQL instance to an ApsaraDB for SelectDB instance" 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 Set filter conditions. If you use the object name mapping feature to rename an object, other objects that depend on the object may fail to be synchronized.

Optional. In the lower part of the page, click Next: Advanced Settings to configure advanced settings.

Parameter	Description
Select the dedicated cluster used to schedule the task	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.
The wait time before a retry when other issues occur in the source and destination databases.	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 The wait time before a retry when other issues occur in the source and destination databases. 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 configure alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see Configure monitoring and alerting when you create a DTS task.

Optional: After you complete the preceding configurations, click Next: Configure Database and Table Fields. Configure the Primary Key Column, Distribution Key, and Engine parameters for the tables to be synchronized to the ApsaraDB for SelectDB instance.

Note

You can perform this step only if you select Schema Synchronization for the Synchronization Types parameter. To modify the parameters, set the Definition Status parameter to All.
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 task fails to pass the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, run a precheck again.
If an alert is generated for an item during the precheck, perform the following operations based on the scenario:
- If the alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issues. Then, run a precheck again.
- If the 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 your subscription when you create an 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. We recommend that you select the pay-as-you-go billing method for short-term use. If you no longer require a pay-as-you-go instance, you can release the instance to reduce costs.
	Resource Group	The resource group to which the instance belongs. Default value: default resource group. For more information, see What is Resource Management?
	Instance Class	DTS provides various synchronization specifications that support different performance. The synchronization speed varies based on the synchronization specifications that you select. You can select a synchronization specification based on your business requirements. For more information, see Specifications of data synchronization instances.
	Subscription Duration	If you select the subscription billing method, set the subscription duration and the number of 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 displayed only if you select the subscription billing method.Subscription

Read and select the Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.

Data type mappings

Category	Data type in MySQL	Data type in ApsaraDB for SelectDB
Numeric value	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 prevent data loss, data of the CHAR and VARCHAR(n) types is converted to the VARCHAR(3*n) type after data is synchronized to ApsaraDB for SelectDB. If you do not specify the length of data, the default value VARCHAR(65533) is used. If the data exceeds 65533 characters in length, the data is converted to strings after it is synchronized to ApsaraDB for SelectDB.
	BINARY VARBINARY	STRING
	TINYTEXT TEXT MEDIUMTEXT LONGTEXT	STRING
	TINYBLOB BLOB MEDIUMBOLB LONGBLOB	STRING
	ENUM	STRING
	SET	STRING
	JSON	STRING

FAQ

Q: What are the differences between the data synchronization and data migration features of DTS?

A: The following table describes the differences between the data migration and data synchronization features.

Item	Data migration	Data synchronization
Scenario	The data migration feature is used to migrate data from on-premises databases, self-managed databases hosted on ECS instances, and databases on third-party clouds to Alibaba Cloud.	The data synchronization feature is used to synchronize data between two data sources in real time. This feature is suitable for scenarios such as active geo-redundancy, disaster recovery, cross-border data synchronization, data query and data streaming for reports, cloud business intelligence (BI) systems, and real-time data warehousing.
Purpose	The data migration feature is generally used to migrate existing historical data.	The data synchronization feature is generally used to migrate existing data and synchronize incremental data in real time.
Billing method	Only the pay-as-you-go billing method is supported.	The pay-as-you-go and subscription billing methods are supported.
Billing rule	You are charged only when incremental data migration is in progress, excluding the period in which incremental data migration is paused. You are not charged for schema migration or full data migration.	If you use the pay-as-you-go billing method, you are charged only when incremental data synchronization is in progress, including the period in which incremental data synchronization is paused. You are not charged for schema synchronization or full data synchronization. If you use the subscription billing method, the fee is deducted based on the quantity and configurations that you specify when you purchase a data synchronization instance.

For more information, see FAQ.

Q: Can I add a field to the source table that is to be synchronized to ApsaraDB for SelectDB?
A: You can perform the ADD COLUMN and DROP COLUMN operations on fields. DTS automatically synchronizes these operations. For more information about the operations that can be incrementally synchronized, see the SQL operations that can be incrementally synchronized section of this topic.
Q: Does DTS synchronize new tables that are created by performing the CREATE TABLE operation?
A: DTS synchronize new tables in the following scenarios:
- If you select databases as the objects to be synchronized, new tables are not synchronized.Source Objects However, you can manually create tables in the destination ApsaraDB for SelectDB instance that correspond to the new tables in the source database. DTS automatically synchronizes the data in the new tables.
- If you select tables as the objects to be synchronized, you can select new tables as the objects to be synchronized. To modify the objects to be synchronized, find the data synchronization task on the Data Synchronization page in the DTS console and click Reselect Objects in the Actions column.Source Objects
Q: What do I do if a table to be synchronized does not have a primary key or UNIQUE constraint?
A:
- The tables to be synchronized from a MySQL database must have primary keys or UNIQUE constraints, and all fields must be unique.
- If you select a database to be synchronized and a table in the database does not have a primary key or UNIQUE constraint, perform the following operations: In the Configure Objects and Advanced Settings step, select Schema Synchronization. In the Configure Database and Table Fields step, use the Unique key model for the table and manually configure the primary key column of the table.

References

Synchronize data from an ApsaraDB RDS for MySQL instance to an ApsaraDB for SelectDB instance

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