Migrate a MySQL database to Tair or Redis - Data Transmission Service

Data Transmission Service (DTS) supports migrating data from MySQL databases, such as self-managed MySQL or RDS MySQL, to Tair (Redis OSS-compatible) to reduce the load on backend relational databases and improve user experience. This topic describes the procedure using an RDS MySQL instance as the source and a Tair (Redis OSS-compatible) instance as the destination.

Prerequisites

The tables in the source database that you want to migrate must have primary keys.
You have created a destination Tair (Redis OSS-compatible) instance. The storage capacity of the destination instance must be greater than the storage space used by the source RDS MySQL instance. For more information about how to create an instance, see Step 1: Create an instance.
Note
For more information about the supported versions of the source and destination databases, see Migration solutions overview.

Considerations

Type	Description
Source database limits	Tables without primary keys cannot be migrated. If you migrate data at the table level and need to edit objects, such as mapping table or column names, a single data migration task can migrate up to 1,000 tables. If you exceed this limit, an error is reported when you submit the task. To resolve this, split the tables into multiple tasks, or configure a task to migrate the entire database. If you want to migrate incremental data, the following requirements for binary logs must be met: The binary logging feature is enabled. The binlog_format parameter is set to row and the binlog_row_image parameter is set to full. Otherwise, error messages are returned during the precheck and the data migration task fails to be started. Important 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. The binary logs of an ApsaraDB RDS for MySQL instance must be stored for at least three days. We recommend that you store the binary logs seven days. The binary logs of a self-managed MySQL database must be 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 reliability or performance stated in the Service Level Agreement (SLA) of DTS may not be guaranteed. Note For more information about how to set Retention Period of the binary logs of an ApsaraDB RDS for MySQL instance, see Configure parameters based on which the system automatically deletes the binary log files of an RDS instance. During full data migration, do not perform DDL operations to change the schema of the database or tables. Otherwise, the data migration task fails. Note During full data migration, DTS queries the source database. This adds metadata locks, which may block DDL operations on the source database. If you perform only full data migration, do not write new data to the source database. Otherwise, data inconsistency occurs between the source and destination databases. To ensure real-time data consistency, select both full data migration and incremental data migration. The data generated by change operation of binary logs, such as data restored from a physical backup or data from a cascade operation, is not recorded and migrated to the destination database when the data migration instance is running. Note If the change data is not recorded and migrated to the destination database, you can migrate full data again on the premise that your business is not affected. If the source database is MySQL database 8.0.23 or later, and the data to be migrated includes invisible columns, the data of the columns cannot be obtained and data loss occurs. Note To make the columns visible, run the `ALTER TABLE <table_name> ALTER COLUMN <column_name> SET VISIBLE;` command. For more information, see Invisible Columns. Tables that do not have primary keys automatically generate invisible primary keys. You need to make the invisible primary keys visible. For more information, see Generated Invisible Primary Keys.
Other limits	If Transparent Data Encryption (TDE) is enabled for the destination instance, you cannot use DTS to migrate data. By default, the maxmemory-policy parameter that specifies how data is evicted is set to volatile-lru for Tair (Redis OSS-compatible) instances. If the destination instance has insufficient memory, data inconsistency may occur between the source and destination instances due to data eviction. In this case, the data synchronization task does not stop running. To prevent data inconsistency, we recommend that you set maxmemory-policy to noeviction for the destination instance. This way, the data synchronization task fails if the destination instance has insufficient memory, but data loss can be prevented for the destination instance. Note For more information about data eviction policies, see What is the default eviction policy? During initial full data synchronization, DTS consumes some resources of the source and destination databases. This may increase the load on the database servers. If your database has heavy traffic or the server specifications are low, the database pressure may increase and even cause the database service to become unavailable. Evaluate the impact on your services before you migrate data. Perform data migration during off-peak hours. If the destination instance is a cluster instance and a shard reaches its memory limit, or if the destination instance has insufficient storage space, the DTS task fails with an Out of Memory error. During the DTS migration, do not allow data writes to the destination database from sources other than DTS. Otherwise, data inconsistency occurs between the source and destination databases. If the source or destination instance is a self-managed Redis instance (the Access Method is not Alibaba Cloud Instance), and its endpoint changes during migration (for example, due to an instance migration or a primary/secondary failover), the migration task may be retried, delayed, or may fail. Data inconsistency may also occur. Check the status of the migration task promptly. If the DTS task is retried, delayed, fails, or encounters other issues, reconfigure the migration task. If any of the following situations occur during data migration, the full data may be migrated to the destination again. This can cause data inconsistency. A transient connection disconnection occurs on the destination Redis instance, causing breakpoint-based data transfer to fail. A primary/secondary switchover or a failover occurs on the destination Redis instance. The endpoint of the destination Redis instance changes. If the always-encrypted (EncDB) feature is enabled for the RDS MySQL instance, full data migration is not supported. Note RDS MySQL instances with Transparent Data Encryption (TDE) enabled support full and incremental data migration. 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, take note of the following limits: If you perform a primary/secondary switchover on the source database when the data migration task is running, the task fails. DTS calculates migration latency based on the timestamp of the latest migrated 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 migration latency may be inaccurate. If the latency of the data migration 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 migrated, 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 limit: In incremental data migration, an ApsaraDB RDS for MySQL instance that does not record transaction logs, such as a read-only ApsaraDB RDS for MySQL V5.6 instance, cannot be used as the source database. DTS executes the CREATE DATABASE IF NOT EXISTS `test` statement in the source database as scheduled to move forward the binary log file position.

Billing

Migration type	Link configuration fee	Data transfer cost
Schema migration and full data migration	Free of charge.	This scenario is free of charge.
Incremental data migration	This is a paid feature. For more information, see Billing overview.	This scenario is free of charge.

SQL operations supported by incremental migration

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE

Database account permissions

Database	Required permissions	How to create and grant permissions
Source RDS MySQL	Read permissions on the objects that you want to migrate.	For more information, see Create an account and Modify account permissions.
Destination Tair (Redis OSS-compatible)	Read and write permissions on the instance.	For more information, see Create and manage accounts.

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	In this example, a database instance of the current Alibaba Cloud account is used. 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 more information about the permission requirements, see Database account permissions.
	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 Tair/Redis.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination Tair (Redis OSS-compatible) instance resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database instance of the current Alibaba Cloud account is used. Select No.
	Instance ID	Select the ID of the destination Tair (Redis OSS-compatible) instance.
	Authentication Method	Select an authentication method based on your business requirements. In this example, select Password Login. Note Only Redis databases of version 6.0 or later support Account + Password Login. If you select Secret-free login, make sure that you enable the password-free access feature in the Redis database. For information about how to enable password-free access for a Tair (Redis OSS-Compatible) instance, see Enable password-free access.
	Database Password	Enter the password to connect to the destination Tair (Redis OSS-compatible) instance. Note The database password must be in the <user>:<password> format. For example, if the custom username of the Redis instance is admin and the password is Rp829dlwa, enter admin:Rp829dlwa.

In the lower part of the page, click Test Connectivity and Proceed.
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	To perform only full data migration, select only Full Data Migration. To ensure service continuity during data migration, select Full Data Migration and Incremental Data Migration. Note If you do not select Incremental Data Migration, we recommend that you do not write data to the source database during data migration. This ensures data consistency between the source and destination databases.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database is empty. If the destination database is empty, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started. Ignore Errors and Proceed: skips the Check the existence of objects in the destination database. check item. Warning If you select Ignore Errors and Proceed, the data in the source database overwrites the data in the destination database that has the same keys as the source data. This may cause data loss in the destination database. Proceed with caution.
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, table, or column level.
Selected Objects	To specify a destination Redis DB, right-click the schema to be migrated in the Selected Objects box. Use the mapping feature to set the following parameters, and then click OK. Mapping Name of Redis/Tair Database (0 to 255): The DB in Redis that receives the data. Enter only a number. Cache Mapping Mode: The format of the data after it is migrated to Redis. Hover over the icon next to an option to view information about it. When Cache Mapping Mode is set to Key-Value Model Based on Database, Table, and Primary Key, you must also set Value Separation Method. Note The mapping feature is not supported for schema names and table names. To select the SQL operations to migrate at the database or table level, right-click the object in the Selected Objects box. In the dialog box that appears, select the SQL operations to migrate. To set a WHERE clause to filter data, right-click the table to be migrated in the Selected Objects box. In the dialog box that appears, set the filter condition. For more information, see Set a filter condition.

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.
Cache Expiration Time	Set the time-to-live (TTL) for keys after data is migrated to Redis, as needed. Important A value of -1 indicates that the keys never expire. This may cause the Redis memory to become full and lead to task errors.
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.
Environment Tag	You can select an environment tag to identify the instance as needed. This topic does not require a selection.
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.

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.