Migrate MySQL data to SelectDB - Data Transmission Service

ApsaraDB for SelectDB provides sub-second responses for massive data queries, supports high-concurrency point queries with tens of thousands of requests, and enables high-throughput complex analytics. You can use Data Transmission Service (DTS) to migrate MySQL databases, such as self-managed MySQL or RDS MySQL, to ApsaraDB for SelectDB for your massive data analytics needs. This topic describes the procedure using an RDS MySQL instance as an example.

Prerequisites

You have created a source RDS MySQL instance and a destination ApsaraDB for SelectDB instance.

Notes

Type	Description
Source database limitations	Bandwidth requirements: The server that hosts the source database must have sufficient outbound bandwidth. Otherwise, the migration speed is affected. Migration object requirements: All tables to be migrated have primary keys or UNIQUE constraints: Ensure that the table fields are unique. Otherwise, duplicate data may exist in the destination database. The migration objects include tables that have neither primary keys nor UNIQUE constraints: When you configure an instance, we recommend that you select Schema Migration for Migration Types and, in the Configurations for Databases, Tables, and Columns step, set Engine for the table to duplicate. Otherwise, the instance may fail or data loss may occur. Note During schema migration, DTS adds fields to the destination table. For more information, see Additional columns. If you migrate objects at the table level and need to edit them, such as mapping table or column names, a single data migration task supports a maximum of 1,000 tables. If you exceed this limit, an error is reported when you submit the task. In this case, split the tables into multiple migration tasks, or configure a task to migrate the entire database. If you perform incremental migration, note the following for binary logs: Binary logging must be enabled. The binlog_format parameter must be set to row, and the binlog_row_image parameter must be set to full. Otherwise, the precheck fails, and the data migration task cannot start. Important If the source self-managed MySQL database is in a dual-primary cluster where each instance is a primary and a secondary of the other, you must enable the log_slave_updates parameter. This ensures that DTS can obtain all binary logs. The binary logs of an RDS for MySQL instance must be retained for at least 3 days. We recommend that you retain them for 7 days. The binary logs of a self-managed MySQL database must be retained for at least 7 days. Otherwise, DTS may fail because it cannot obtain the binary logs. In extreme cases, this can 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 the binary logs of an RDS for MySQL instance, see Automatically delete binary logs. During the schema migration and full migration phases, do not perform DDL operations that change the database or table schema. Otherwise, the data migration task will fail. Note During the full migration phase, DTS queries the source database. This creates a metadata lock, which may block DDL operations on the source database. If you perform only a full data migration, do not write new data to the source database. Otherwise, data inconsistency will occur between the source and destination databases. To maintain real-time data consistency, select schema migration, full data migration, and incremental data migration. Data changes from operations that are not recorded in binary logs during the migration are not migrated to the destination database. Examples of such operations include data recovery using physical backup and cascade operations. Note If this occurs, you can perform a full data migration again when your business permits. If the source database is MySQL 8.0.23 or later and the data to be migrated contains invisible columns, data loss may occur because the data in these columns cannot be obtained. 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.
Other limitations	Currently, you can migrate data only to tables that use the Unique or Duplicate engine in the SelectDB instance. Destination table uses the Unique engine If the destination table uses the Unique engine, make sure that all unique keys in the destination table also exist in the source table and are included in the migration objects. Otherwise, data inconsistency may occur. Destination table uses the Duplicate engine If the destination table uses the Duplicate engine, duplicate data may exist in the destination database in the following cases. You can remove duplicate data based on the additional columns (_is_deleted, _version, and _record_id): The migration instance was retried. The migration instance was restarted. After the migration instance starts, two or more DML operations were performed on the same data record to be migrated. Note When the destination table uses the Duplicate engine, DTS converts UPDATE or DELETE statements into INSERT statements. You cannot migrate INDEX, PARTITION, VIEW, PROCEDURE, FUNCTION, TRIGGER, or FK objects. When you configure parameters in the Selected Objects box, you can currently only set the `bucket_count` parameter (number of buckets). Note The value for the `bucket_count` parameter can only be a positive integer. The default value is auto. During data migration, do not create a new cluster in the destination SelectDB instance. Otherwise, the task fails. You can try to restart the migration instance to recover the failed task. SelectDB instances support only database and table names that start with a letter. If the name of a database or table to be migrated does not start with a letter, you must use the mapping feature to change the name. If the name of a migration object (database, table, or column) contains Chinese characters, you must use the mapping feature to change the name, for example, to English. Otherwise, the task may fail. You cannot migrate DDL operations that modify multiple columns at a time or DDL operations that continuously modify the same table. During data migration, do not add backend (BE) nodes to the SelectDB database. Otherwise, the task fails. You can try to restart the migration instance to recover the failed task. In a multi-table merge scenario, where data from multiple source tables is migrated to a single destination table, ensure that the source tables have the same schema. Otherwise, data inconsistency or task failure may occur. In MySQL, M in `VARCHAR(M)` specifies the character length. In SelectDB, N in `VARCHAR(N)` specifies the byte length. If you do not use the schema migration feature of DTS, we recommend that you set the length of VARCHAR fields in SelectDB to four times the length of the corresponding VARCHAR fields in MySQL. When you use DMS or the gh-ost tool to perform online DDL operations on the source, DTS migrates only the original DDL statements to the destination. In this scenario, DTS does not need to migrate a large amount of temporary table data, but this may cause locked tables at the destination. Note You cannot migrate online DDL changes made using tools such as pt-online-schema-change on the source. If such changes exist on the source, data loss may occur at the destination, or the migration instance may fail. Before you migrate data, evaluate the performance of the source and destination databases. We recommend that you perform data migration during off-peak hours. Otherwise, initial full data synchronization consumes read and write resources on both the source and destination databases, which may increase database workloads. Initial full synchronization concurrently executes INSERT operations. This causes table fragmentation in the destination database. As a result, the tablespace of the destination instance is larger than that of the source instance after the initial full synchronization is complete. During data migration, do not use tools such as pt-online-schema-change to perform online DDL changes on the migration objects in the source database. Otherwise, the migration fails. During data migration, if data is written to the destination database by sources other than DTS, data inconsistency may occur between the source and destination databases. If the always-encrypted (EncDB) feature is enabled for the RDS for MySQL instance, full data migration is not supported. Note RDS for MySQL instances with Transparent Data Encryption (TDE) enabled support schema migration, full data migration, and incremental data migration. During incremental migration, DTS uses a batch synchronization policy to reduce the load on the destination. By default, for a single synchronization object, DTS writes data at most once every 5 seconds. Therefore, a normal synchronization latency, usually within 10 seconds, may occur for the DTS migration task. To reduce this normal migration latency, modify the `selectdb.reservoir.timeout.milliseconds` parameter for the DTS instance in the console to adjust the batching time. The value can range from 1,000 to 10,000 milliseconds. Note When you adjust the batching time, a shorter time increases the write frequency of DTS. This may increase the load and response time (RT) of writes at the destination, which in turn increases the DTS synchronization latency. Adjust the time based on the load of the destination. 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 or adjusting its parameters may be performed. Note When parameters are adjusted, only the parameters of the DTS instance are modified. The parameters in 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	When the source database is a self-managed MySQL database: A primary/secondary switchover in the source database during migration causes the migration task to fail. The latency of DTS is calculated by comparing the timestamp of the last migrated data record with the current timestamp. 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 migrate 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 clustered MySQL instance, ensure that the domain name or IP address configured for the task and its resolved result always point to the read/write (RW) node. Otherwise, the migration task may not run as expected. When the source database is an RDS for MySQL instance: To migrate incremental data, RDS for MySQL instances that do not record transaction logs, such as read-only instances of RDS for MySQL 5.6, cannot be used as the source database. DTS periodically runs the CREATE DATABASE IF NOT EXISTS `test` command on the source database to advance the binary log offset.

Billing details

Migration type	Link configuration fee	Data transfer cost
Schema migration and full data migration	Free of charge.	This example is free of charge. Note When the Access Method of the destination database is Public IP Address, data transfer costs apply. For more information, see Billing overview.
Incremental data migration	Billed. For more information, see Billing overview.

SQL statements supported for incremental migration

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE
DDL	ADD COLUMN MODIFY COLUMN CHANGE COLUMN DROP COLUMN, DROP TABLE TRUNCATE TABLE RENAME TABLE Important RENAME TABLE operations may cause data inconsistency between the source and destination databases. For example, if you select a table as the object to be migrated and rename the table during data migration, the data of this table is not migrated to the destination database. To prevent this situation, you can select the database to which this table belongs as the object to be migrated when you configure the data migration task. Make sure that the databases to which the table belongs before and after the RENAME TABLE operation are added to the objects to be migrated.

Permissions required for database accounts

Database	Schema migration	Full migration	Incremental migration
Source RDS MySQL	SELECT permission	The SELECT permission	Read/write
Destination SelectDB	Cluster access permissions (Usage_priv) and database read/write permissions (Select_priv, Load_priv, Alter_priv, Create_priv, Drop_priv)

To create a database account and grant permissions:

For an RDS MySQL instance, see Create an account and Modify the permissions of an account.
For a SelectDB instance, see Cluster Permission Management and Basic Permission Management.

Note

If the source database account is not created and granted permissions in the RDS MySQL console, you must 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 Migration page and select the region in which the data migration instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Migration.
3. In the upper-left corner of the page, select the region in which the data migration instance resides.
DMS console
Note
The actual operation 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 > DTS (DTS) > Data Migration.
3. From the drop-down list to the right of Data Migration 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	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source RDS MySQL instance resides.
	Replicate Data Across Alibaba Cloud Accounts	This example is for a migration within the same Alibaba Cloud account. Select No.
	RDS Instance ID	Select the ID of the source RDS MySQL instance.
	Database Account	Enter the database account of the source RDS 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 SelectDB.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination SelectDB instance resides.
	Replicate Data Across Alibaba Cloud Accounts	This example is for a migration within the same Alibaba Cloud account. Select No.
	Instance ID	Select the ID of the destination SelectDB instance.
	Database Account	Enter the database account of the destination SelectDB instance. For information about the required permissions, see Permissions required for database accounts.
	Database Password	The password that is used to access the database instance.

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 migrated.

On the Configure Objects page, configure the objects that you want to migrate.

Configuration	Description
Migration Types	If you only need to perform a full data migration, select both Schema Migration and Full Data Migration. To perform a zero-downtime migration, select Schema Migration, Full Data Migration, and Incremental Data Migration. Important When data is migrated from MySQL to SelectDB, data types are converted. If you do not select Schema Migration, you must create Unique or Duplicate model tables with the corresponding structure in the target SelectDB in advance. For more information, see Data Type Mapping, Additional Column Information, and Data Model. If you do not select Incremental Data Migration, to ensure data consistency, do not write new data to the source instance during the data migration.
Processing Mode of Conflicting Tables	Precheck and Report Errors: Checks if a table with the same name exists in the target database. If no table with the same name exists, this check item is passed. If a table with the same name exists, an error is reported during the precheck phase and the data migration task will not be started. Note If you cannot delete or rename the table with the same name in the destination database, you can change the name of the table in the destination database. For more information, see Map table and column names. Ignore Errors and Proceed: Skips the check for whether a table with the same name exists in the target database. Warning Selecting Ignore Errors and Proceed may lead to data inconsistency and pose risks to your business. For example: If the table schemas are consistent and DTS encounters a record in the destination database that has the same primary key value as a record in the source database, DTS does not retain the record in the destination cluster. The record from the source database overwrites the record in the destination database. If the table schemas are inconsistent, only data from some columns may be migrated, or the migration may fail. 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 make sure that the capitalization of object names is consistent with that of 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. Click the icon to add the objects to the Selected Objects section. Note You can select objects to migrate at the database or table level.
Selected Objects	To rename a migration object in the destination instance, right-click the migration object in Selected Objects. For more information, see Schema, table, and column name mapping. If Migration Types is set to Schema Migration, objects are selected at the table granularity, and you need to set the bucketing count (the `bucket_count` parameter), right-click the table to be migrated in the Selected Objects list. In the Parameter Settings area, set Enable Parameter Settings to Yes, set the Value based on your requirements, and then click OK. Note To select SQL operations for incremental migration at the database or table level, right-click the object to be migrated in Selected Objects and select the desired SQL operations in the dialog box that appears. To set a WHERE condition to filter data, right-click the table to be migrated in the Selected Objects section and set the filter condition in the dialog box that appears. For more information, see Set filter conditions. If you use the object name mapping feature, the migration of other objects that depend on the mapped object may fail.

Click Next: Advanced Settings to configure advanced settings.

Configuration	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the data migration task to the shared cluster if you do not specify a dedicated cluster. 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 migration task is started, DTS immediately retries a connection within the retry time range. Valid values: 10 to 1,440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS is reconnected to the source and destination databases within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you specify different retry time ranges for multiple data migration tasks that share the same source or destination database, the value that is specified later 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 the earliest opportunity after the source database and destination instance are released.
Retry Time for Other Issues	The retry time range for other issues. For example, if DDL or DML operations fail to be performed after the data migration task is started, DTS immediately retries the operations within the retry time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set the parameter to a value greater than 10. If the failed operations are successfully performed within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration 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	Specifies whether to enable throttling for full data migration. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. You can enable throttling for full data migration based on your business requirements. To configure throttling, you must 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. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Full Data Migration for the Migration Types parameter.
Enable Throttling for Incremental Data Migration	Specifies whether to enable throttling for incremental data migration. To configure throttling, you must configure the RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Incremental Data Migration for the Migration Types parameter.
Environment Tag	You can select an environment tag to identify the instance as needed. In this example, no selection is required.
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 migration task. If the task fails or the migration latency exceeds the specified threshold, the alert contacts 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 the Configure monitoring and alerting when you create a DTS task section of the Configure monitoring and alerting topic.

Optional: After you complete the preceding configurations, click Next: Configure Database and Table Fields to set the Primary Key Column, Distribution Key, and Engine for the destination tables.
Note
- This step is available only if you select Schema Migration for Migration Types during task object configuration. You can then select All for Definition Status to make modifications.
- The Primary Key Column can be a composite primary key that consists of multiple columns. You must select one or more columns from the Primary Key Column as the Distribution Key.
- If a table has neither a primary key nor a UNIQUE constraint, you must set the Engine to duplicate. Otherwise, this may cause instance failure or data loss.

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 migration task, DTS performs a precheck. You can start the data migration 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 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 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.

Purchase the instance.

Wait until Success Rate becomes 100%. Then, click Next: Purchase Instance.

On the Purchase Instance page, configure the Instance Class parameter for the data migration instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Resource Group	The resource group to which the data migration instance belongs. Default value: default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Instance classes of data migration instances.

Read and agree to Data Transmission Service (Pay-as-you-go) Service Terms by selecting the check box.
Click Buy and Start. In the message that appears, click OK.
You can view the progress of the task on the Data Migration page.
Note
- If a data migration task cannot be used to migrate incremental data, the task automatically stops. The Completed is displayed in the Status section.
- If a data migration task can be used to migrate incremental data, the task does not automatically stop. The incremental data migration task never stops or completes. The Running is displayed in the Status section.

Data type mapping

Category	MySQL data type	SelectDB data type
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 The zerofill attribute 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 VARCHAR(4*n) after being migrated to SelectDB. If no data length is specified, the default value of SelectDB, VARCHAR(65533), is used. If the data length exceeds 65533, the data is converted to STRING after being migrated to SelectDB.
	BINARY VARBINARY	STRING
	TINYTEXT TEXT MEDIUMTEXT LONGTEXT	STRING
	TINYBLOB BLOB MEDIUMBOLB LONGBLOB	STRING
	ENUM	STRING
	SET	STRING
	JSON	STRING

Additional columns

Note

The following table describes the additional columns that are automatically added by DTS or that you must add manually to a destination table that uses the Duplicate model.

Name	Data type	Default value	Description
_is_deleted	Int	0	Indicates whether the data is deleted. Insert: The value is 0. Update: The value is 0. Delete: The value is 1.
_version	Bigint	0	For full data migration: The value is 0. For incremental data migration: The value is the corresponding timestamp (in seconds) in the binary log of the source database.
_record_id	Bigint	0	For full data migration: The value is 0. For incremental data migration: The value is the record ID in the incremental log. This ID uniquely identifies the log. Note The ID value is unique and incremental.

Prerequisites

Notes

Destination table uses the Unique engine

Destination table uses the Duplicate engine