Synchronize a MySQL database to Redis - Data Transmission Service

Data Transmission Service (DTS) supports synchronizing data from MySQL databases, such as self-managed MySQL or RDS for MySQL, to Tair (Redis OSS-compatible). This reduces the load on your backend relational database and improves user experience. This topic describes how to synchronize data from an RDS for MySQL instance to a Tair (Redis OSS-compatible) instance.

Prerequisites

The source database tables to be synchronized must have primary keys.
Create a destination Tair (Redis OSS-compatible) instance with more storage space than is used by the source RDS for MySQL instance. For more information, see Step 1: Create an instance.
Note
For the supported versions of the source and destination databases, see Synchronization solutions.

Notes

Type	Description
Source database limits	Tables without primary keys cannot be synchronized. If you synchronize data at the table level and need to edit objects, such as mapping table or column names, a single synchronization task supports a maximum of 1,000 tables. If you exceed this limit, an error is reported after you submit the task. In this case, split the tables into multiple synchronization tasks or configure a task to synchronize the entire database. Binary logs: Binary logging is enabled for ApsaraDB RDS for MySQL instances by default. You must make sure that the `binlog_row_image` parameter is set to `full`. Otherwise, a precheck error is reported and the data synchronization task cannot start. For more information about how to set parameters, see Set instance parameters. Important If the source instance is a self-managed MySQL database, you must enable binary logging and set the `binlog_format` parameter to `row` and the `binlog_row_image` parameter to `full`. If the source self-managed MySQL database is in a primary/primary architecture where the two databases are the primary and secondary of each other, you must enable the `log_slave_updates` parameter. This ensures that DTS can obtain all binary logs. For more information, see Create a database account for a self-managed MySQL database and configure binary logging. The local binary logs of an ApsaraDB RDS for MySQL instance must be retained for at least 3 days. We recommend that you retain them for 7 days. The local binary logs of a self-managed MySQL database must be retained for at least 7 days. Otherwise, the DTS task may fail because DTS cannot obtain the binary logs. In extreme cases, data may be inconsistent or lost. Issues that are caused by a binary log retention period shorter than the required period are not covered by the DTS Service-level agreement (SLA). Note For more information about how to set the Retention Period for local binary logs of an ApsaraDB RDS for MySQL instance, see Automatically delete local logs. During full data synchronization, do not perform DDL operations to change the schemas of databases or tables. Otherwise, the data synchronization task fails. During the runtime of the DTS instance, data changes from operations that are not recorded in binary logs are not synchronized to the destination database. Examples of such operations include data recovery using physical backups and cascade operations. Note If this occurs, you can remove the database or table from the synchronization objects and then add it back. This is allowed if your business permits. For more information, see Modify synchronization objects. If the source database is MySQL 8.0.23 or later and the data to be synchronized contains invisible columns, data may be lost because DTS cannot obtain the data of these columns. Note You can run the `ALTER TABLE <table_name> ALTER COLUMN <column_name> SET VISIBLE;` command to make the invisible columns visible. For more information, see Invisible Columns. Tables without a primary key automatically generate an invisible primary key. You must also make this invisible primary key visible. For more information, see Generated Invisible Primary Keys.
Other limits	If Transparent Data Encryption (TDE) is enabled for the destination instance, you cannot use DTS to synchronize 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, which may increase the database server load. If your database has heavy traffic or the server specifications are low, the pressure on the database may increase, and the database service may even become unavailable. Before you synchronize data, carefully assess the impact. Perform data synchronization 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 (OOM) error. During DTS synchronization, do not write data to the destination database using methods other than DTS. Otherwise, data inconsistency between the source and destination databases occurs. If the source Redis instance is scaled in or out (shards are added or removed) or its specifications are changed (memory is scaled up) during synchronization, you must reconfigure the task. To ensure data consistency, clear the data in the destination Redis instance before you reconfigure the task. If any of the following situations occur during data synchronization, full data may be resynchronized to the destination, which can cause data inconsistency. A transient connection disconnection occurs on the source or destination Redis instance, causing breakpoint-based data transfer to fail. A primary/secondary switchover or a failover occurs on the source or destination Redis instance. The endpoint of the source or destination Redis instance changes. The synchronization objects of the DTS instance are modified. If the always-encrypted feature is enabled for the RDS for MySQL instance, full data synchronization is not supported. Note RDS for MySQL instances with TDE enabled support full and incremental data synchronization. If an instance fails, DTS helpdesk will try to recover the instance within 8 hours. During the recovery process, operations such as restarting the instance and adjusting parameters may be performed. Note When parameters are adjusted, only the parameters of the DTS instance are modified. The parameters of the database are not modified. The parameters that may be modified include but are not limited to those described in Modify instance parameters.
Special cases	If the source database is a self-managed MySQL database: If a primary/secondary failover occurs in the source database during synchronization, the sync task fails. The latency of DTS is calculated based on the difference between the current timestamp and the timestamp of the last data record synchronized to the destination database. If no DML operations are performed on the source database for a long time, the latency information may be inaccurate. If the displayed latency is too high, you can perform a DML operation on the source database to update the latency information. Note If you choose to synchronize the entire database, you can also create a heartbeat table. The heartbeat table is updated or written to every second. DTS periodically runs the CREATE DATABASE IF NOT EXISTS `test` command on the source database to advance the binary log offset. If the source database is an Amazon Aurora MySQL instance or another MySQL instance in cluster mode, make sure that the domain name or IP address configured for the task and its resolution result always point to the read/write (RW) node. Otherwise, the sync task may not run properly. If the source database is an ApsaraDB RDS for MySQL instance: ApsaraDB RDS for MySQL instances that do not record transaction logs, such as read-only instances of ApsaraDB RDS for MySQL 5.6, cannot be used as a source database. DTS periodically runs the CREATE DATABASE IF NOT EXISTS `test` command on the source database to advance the binary log offset.

Billing

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

SQL statements for incremental synchronization

Operation type	SQL statements
DML	INSERT, UPDATE, DELETE

Permissions for database accounts

Database	Required permissions	Creation and authorization method
Source RDS for MySQL	Read permissions on the objects to be synchronized.	See Create a database account for an ApsaraDB RDS for MySQL instance and Modify the permissions of a database account for an ApsaraDB RDS for MySQL instance.
Destination Tair (Redis OSS-compatible)	Read and write permissions on the instance.	See Create and manage a database account.

Procedure

Use one of the following methods to go to the Data Synchronization page and select the region in which the data synchronization instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Synchronization.
3. In the upper-left corner of the page, select the region in which the data synchronization task resides.
DMS console
Note
The actual operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Customize the layout and style of the DMS console.
1. Log on to the DMS console.
2. In the top navigation bar, move the pointer over Data + AI and choose DTS (DTS) > Data Synchronization.
3. From the drop-down list to the right of Data Synchronization Tasks, select the region in which the data synchronization instance resides.
Click Create Task to go to the task configuration page.

Configure the source and destination databases. The following table describes the parameters.

Category	Configuration	Description
None	Task Name	The name of the DTS task. DTS automatically generates a task name. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to specify a unique task name.
Source Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	Select MySQL.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region of the source RDS for MySQL instance.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database of the current Alibaba Cloud account is used. Select No.
	RDS Instance ID	Select the ID of the source RDS for MySQL instance.
	Database Account	Enter the database account for the source RDS for MySQL instance. For permission requirements, see Permissions 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 Tair/Redis.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region of the destination Tair (Redis OSS-compatible) instance.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database 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 password format is <user>:<password>. For example, if the custom username of the Redis instance is `admin` and the password is `Rp829dlwa`, enter `admin:Rp829dlwa`.

Click Test Connectivity and Proceed in the lower part of the page.
Note
- Make sure that the CIDR blocks of DTS servers can be automatically or manually added to the security settings of the source and destination databases to allow access from DTS servers. For more information, see Add DTS server IP addresses to a whitelist.
- If the source or destination database is a self-managed database and its Access Method is not set to Alibaba Cloud Instance, click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

Configure the objects to be synchronized.

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

Configuration	Description
Synchronization Types	Incremental Data Synchronization is selected by default. To synchronize historical data, also select Full Data Synchronization.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether data exists in the destination database. If no data exists in the destination database, the precheck is passed. If data exists in the destination database, an error is returned during the precheck, and the data synchronization instance 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, data loss may occur in the destination database because data records in the source database overwrite the data records that have the same keys in the destination database. Proceed with caution.
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 objects at the database, table, and column levels.
Selected Objects	To specify a destination Redis DB, right-click the schema to be synchronized 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 synchronized to Redis. Hover over the icon next to the option to view information. 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 SQL operations to synchronize at the database or table level, right-click the object in the Selected Objects box and select the desired SQL operations in the dialog box that appears. To set a WHERE clause to filter data, right-click the table in the Selected Objects box and set the filter condition in the dialog box that appears. For instructions, see Filter data.

Click Next: Advanced Settings to configure advanced settings.

Configuration	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data synchronization instances, purchase a dedicated cluster. For more information, see What is a DTS dedicated cluster.
Retry Time for Failed Connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data synchronization task is started, DTS immediately retries a connection within the time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set this parameter to a value greater than 30. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Note If you specify different retry time ranges for multiple data synchronization tasks that have the same source or destination database, the shortest retry time range takes precedence. When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
Retry Time for Other Issues	The retry time range for other issues. For example, if the DDL or DML operations fail to be performed after the data synchronization task is started, DTS immediately retries the operations within the time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set this parameter to a value greater than 10. If the failed operations are successfully performed within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Important The value of the Retry Time for Other Issues parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Full Data Synchronization	During full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the load on the database servers. You can configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters for full data synchronization tasks to reduce the load on the destination database server. Note You can configure this parameter only if Full Data Synchronization is selected for the Synchronization Types parameter.
Enable Throttling for Incremental Data Synchronization	Specifies whether to enable throttling for incremental data synchronization. You can enable throttling for incremental data synchronization based on your business requirements. To configure throttling, you must configure the RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s) parameters. This reduces the load on the destination database server.
Cache Expiration Time	Set the time-to-live (TTL) for keys after data is synchronized to Redis, based on your requirements. Important A value of -1 means the key never expires. This may cause Redis to run out of memory and cause the task to fail.
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 based on your requirements. For this example, you do not need to select a tag.
Configure ETL	Specifies whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.
Monitoring and Alerting	Specifies whether to configure alerting for the data synchronization instance. If the task fails or the synchronization latency exceeds the specified threshold, alert contacts will receive notifications. Valid values: No: does not enable alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see the "Configure monitoring and alerting when you create a DTS task" section of the Configure monitoring and alerting topic.

Save the task settings and run a precheck.
- To view the parameters to be specified when you call the relevant API operation to configure the DTS task, move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters.
- If you do not need to view or have viewed the parameters, click Next: Save Task Settings and Precheck in the lower part of the page.
Note
- Before you can start the data synchronization task, DTS performs a precheck. You can start the data synchronization task only after the task passes the precheck.
- If the data synchronization task fails the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, rerun the precheck.
- If an alert is triggered for an item during the precheck:
  If an alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issue. Then, run a precheck again.
  If an alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur, and your business may be exposed to potential risks.

Purchase the instance.

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

On the buy page, configure the Billing Method and Instance Class parameters for the data synchronization task. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Billing Method	Subscription: You pay for a subscription when you create a data synchronization instance. The subscription billing method is more cost-effective than the pay-as-you-go billing method for long-term use. Pay-as-you-go: A pay-as-you-go instance is billed on an hourly basis. The pay-as-you-go billing method is suitable for short-term use. If you no longer require a pay-as-you-go data synchronization instance, you can release the instance to reduce costs.
	Resource Group Settings	The resource group to which the data synchronization instance belongs. Default value: default resource group. For more information, see What is Resource Management?
	Instance Class	DTS provides instance classes that vary in synchronization speed. You can select an instance class based on your business requirements. For more information, see Instance classes of data synchronization instances.
	Subscription Duration	If you select the subscription billing method, specify the subscription duration and the number of data synchronization instances that you want to create. The subscription duration can be one to nine months, one year, two years, three years, or five years. Note This parameter is available only if you select the Subscription billing method.

Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start. In the dialog box that appears, click OK.
You can view the progress of the task in the task list.