Synchronize a MySQL database to Redis - Data Transmission Service

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: ApsaraDB RDS for MySQL enables binary logging by default. Ensure that the binlog_row_image parameter is set to full. Otherwise, the precheck fails and the synchronization task cannot start. For instructions, see Configure instance parameters. Important If your source instance is a self-managed MySQL database, enable binary logging and set binlog_format to row and binlog_row_image to full. If your self-managed MySQL database is a dual-primary cluster (where both nodes act as primary and secondary), enable the log_slave_updates parameter so DTS can capture all binary log events. For instructions, see Create an account and configure binary logging for a self-managed MySQL database. The local binary logs for an ApsaraDB RDS for MySQL instance must be retained for at least three days (seven days is recommended). For a self-managed MySQL database, retain local binary logs for at least seven days. Otherwise, DTS may fail to retrieve binary logs, causing the task to fail. In extreme cases, this may cause data inconsistency or data loss. Issues caused by binary log retention periods shorter than DTS requires are not covered under the DTS SLA. Note To configure the retention period for local binary logs on an ApsaraDB RDS for MySQL instance, see Automatically delete local logs. During the full data synchronization phase, do not perform DDL operations that change database or table schemas. Otherwise, the data synchronization task fails. Note During the full data synchronization phase, DTS queries the source database, which generates metadata locks that may block DDL operations on the source database. Data generated by changes that do not write to binary logs—such as data restored from physical backups or created by cascade operations—is not synchronized to the destination database. Note If this occurs, remove the affected database or table from the synchronization objects. Then add it back. You can do this only if your business allows it. For more information, see Modify synchronization objects. If your source database is MySQL 8.0.23 or later and contains invisible hidden columns, DTS may not read those columns. This may cause data loss. Note Run the `ALTER TABLE <table_name> ALTER COLUMN <column_name> SET VISIBLE;` command to make the hidden column visible. For more information, see Invisible Columns.
Other limits	If Transparent Data Encryption (TDE) is enabled for the destination instance, you cannot use DTS to synchronize data. If the destination runs out of memory, data eviction may cause inconsistency between the source and destination. The default maxmemory-policy for Tair (Redis OSS-Compatible) is volatile-lru, which does not affect task operation but may evict data. Set the destination eviction policy to noeviction to prevent data loss. With this policy, write operations fail and the task stops when memory is exhausted, but no data is evicted. Note Data eviction policies in Redis. 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. Operations on the source or target Redis instance during synchronization, such as scaling, changing specifications, migrating availability zones, or changing the endpoint or port, can interrupt the task. DTS cannot obtain continuous log data or correct connection information. If this occurs, clear the synchronized data from the target 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 a task fails, DTS support staff will attempt to restore it within eight hours. During restoration, they may restart the task or adjust its parameters. Note Only DTS task parameters are modified—not database parameters. Parameters that may be adjusted include those listed in Modify instance parameters.
Special cases	For a self-managed MySQL source database: If a primary/secondary switchover occurs in the source database during synchronization, the task fails. DTS calculates latency by comparing the timestamp of the last synchronized record with the current time. If no DML operations run for a long time in the source database, latency reporting may become inaccurate. If latency appears too high, run a DML operation in the source database to update the latency. Note If you select a full database for synchronization, create a heartbeat table. Update or write to this table every second. DTS periodically runs the CREATE DATABASE IF NOT EXISTS `test` command in the source database to advance the binary log offset. If your source database is Amazon Aurora MySQL or another clustered MySQL instance, ensure the domain name or IP address used in the task configuration—and its DNS resolution—always points to a read/write (RW) node. Otherwise, synchronization may fail. For an ApsaraDB RDS for MySQL source database: Read-only instances—such as ApsaraDB RDS for MySQL 5.6 read-only instances—that do not record transaction logs cannot serve as source databases. DTS periodically runs the CREATE DATABASE IF NOT EXISTS `test` command in the source database to advance the binary log offset.

Billing

Synchronization type	Pricing
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

Go to the data synchronization task list page in the destination region. You can do this in one of two ways.
DTS console
1. Log on to the DTS console.
2. In the navigation pane on the left, click Data Synchronization.
3. In the upper-left corner of the page, select the region where the synchronization instance is located.
DMS console
Note
The actual steps may vary depending on the mode and layout of the DMS console. For more information, see Simple mode console and Customize DMS console layout and style.
1. Log on to the DMS console.
2. In the top menu bar, choose Data + AI > DTS (DTS) > Data Synchronization.
3. To the right of Data Synchronization Tasks, select the region of the synchronization instance.
Click Create Task to open the task configuration page.

Configure the source and destination databases.

Category	Configuration	Description
None	Task Name	DTS automatically generates a task name. We recommend that you specify a descriptive name for easy identification. The name does not need to be unique.
Source Database	Select Existing Connection	Select the registered database instance with DTS from the drop-down list. The database information below is automatically configured. Note In the DMS console, this configuration item is Select a DMS database instance. If you have not registered the database instance or do not need to use a registered instance, manually configure the database information below.
	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	For this example, select No, as the database instance belongs to the current Alibaba Cloud account.
	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	Enter the password for the specified database account.
	Encryption	Select Non-encrypted or SSL-encrypted as needed. If you set this to SSL-encrypted, you must enable SSL encryption for the RDS for MySQL instance beforehand. For more information, see Use a cloud certificate to quickly enable SSL link encryption.
Destination Database	Select Existing Connection	Select the registered database instance with DTS from the drop-down list. The database information below is automatically configured. Note In the DMS console, this configuration item is Select a DMS database instance. If you have not registered the database instance or do not need to use a registered instance, manually configure the database information below.
	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	For this example, select No, as the database instance belongs to the current Alibaba Cloud account.
	Instance ID	Select the ID of the destination Tair (Redis OSS-compatible) instance.
	Authentication Method	Select an authentication method based on your requirements. In this example, Password Login is selected. Note Only Redis 6.0 and later support Account + Password Login. If you select Secret-free login, make sure that password-free access is enabled for the Redis database. For information about how to enable password-free access for a Tair (Redis OSS-Compatible) instance, see Enable password-free access over a VPC.
	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`.

After completing the configuration, click Test Connectivity and Proceed at the bottom of the page.
Note
- Ensure that you add the CIDR blocks of the DTS servers (either automatically or manually) to the security settings of both the source and destination databases to allow access. For more information, see Add the IP address whitelist of DTS servers.
- If the source or destination is a self-managed database (i.e., the Access Method is not Alibaba Cloud Instance), you must also click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

Configure the task objects.

On the Configure Objects page, specify the objects 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 if the destination is empty. If the destination is empty, the precheck is successful. If the destination is not empty, an error is reported during the precheck, and the data synchronization job does not start. Ignore Errors and Proceed: Skips the Check the existence of objects in the destination database. precheck. Warning If you select Ignore Errors and Proceed, source data overwrites destination data if the same key exists in both the source and destination. This may cause data loss in the destination. Select this option with caution.
Source Objects	In the Source Objects box, click the objects, and then click to move them to the Selected Objects box. 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.

Configuration	Description
Dedicated Cluster for Task Scheduling	By default, DTS uses a shared cluster for tasks, so you do not need to make a selection. For greater task stability, you can purchase a dedicated cluster to run the DTS synchronization task. For more information, see What is a DTS dedicated cluster?.
Retry Time for Failed Connections	If the connection to the source or destination database fails after the synchronization task starts, DTS reports an error and immediately begins to retry the connection. The default retry duration is 720 minutes. You can customize the retry time to a value from 10 to 1,440 minutes. We recommend a duration of 30 minutes or more. If the connection is restored within this period, the task resumes automatically. Otherwise, the task fails. Note If multiple DTS instances (e.g., Instance A and B) share a source or destination, DTS uses the shortest configured retry duration (e.g., 30 minutes for A, 60 for B, so 30 minutes is used) for all instances. DTS charges for task runtime during connection retries. Set a custom duration based on your business needs, or release the DTS instance promptly after you release the source/destination instances.
Retry Time for Other Issues	If a non-connection issue (e.g., a DDL or DML execution error) occurs, DTS reports an error and immediately retries the operation. The default retry duration is 10 minutes. You can also customize the retry time to a value from 1 to 1,440 minutes. We recommend a duration of 10 minutes or more. If the related operations succeed within the set retry time, the synchronization task automatically resumes. Otherwise, the task fails. Important The value of Retry Time for Other Issues must be less than that of Retry Time for Failed Connections.
Enable Throttling for Full Data Synchronization	During full data synchronization, DTS consumes read and write resources from the source and destination databases, which can increase their load. To mitigate pressure on the destination database, you can limit the migration rate by setting Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s). Note This parameter is available only if Synchronization Types is set to Full Data Synchronization. You can also adjust the rate of full data synchronization when the synchronization instance is running.
Enable Throttling for Incremental Data Synchronization	You can also limit the incremental synchronization rate to reduce pressure on the destination database by setting RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s).
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	Choose whether DTS writes heartbeat SQL information to the source database while the instance is running. Yes: Does not write heartbeat SQL information to the source database. The DTS instance may display latency. No: Writes heartbeat SQL information to the source database. This may interfere with source database operations like physical backups and cloning.
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	Choose whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: Enables the ETL feature. Enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: Disables the ETL feature.
Monitoring and Alerting	Choose whether to set up alerts. If the synchronization fails or the latency exceeds the specified threshold, DTS sends a notification to the alert contacts. No: No alerts are configured. Yes: Configures alerts. You must also set the alert threshold and alert notifications. For more information, see Configure monitoring and alerting during task configuration.

Save the task and perform a precheck.
- To view the parameters for configuring this instance via an API operation, hover over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the tooltip.
- If you have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.
Note
- Before a synchronization task starts, DTS performs a precheck. You can start the task only if the precheck passes.
- If the precheck fails, click View Details next to the failed item, fix the issue as prompted, and then rerun the precheck.
- If the precheck generates warnings:
  For non-ignorable warning, click View Details next to the item, fix the issue as prompted, and run the precheck again.
  For ignorable warnings, you can bypass them by clicking Confirm Alert Details, then Ignore, and then OK. Finally, click Precheck Again to skip the warning and run the precheck again. Ignoring precheck warnings may lead to data inconsistencies and other business risks. Proceed with caution.

Purchase the instance.

When the Success Rate reaches 100%, click Next: Purchase Instance.

On the Purchase page, select the billing method and link specifications for the data synchronization instance. For more information, see the following table.

Category	Parameter	Description
New Instance Class	Billing Method	Subscription: You pay upfront for a specific duration. This is cost-effective for long-term, continuous tasks. Pay-as-you-go: You are billed hourly for actual usage. This is ideal for short-term or test tasks, as you can release the instance at any time to save costs.
	Resource Group Settings	The resource group to which the instance belongs. The default is default resource group. For more information, see What is Resource Management?.
	Instance Class	DTS offers synchronization specifications at different performance levels that affect the synchronization rate. Select a specification based on your business requirements. For more information, see Data synchronization link specifications.
	Subscription Duration	In subscription mode, select the duration and quantity of the instance. Monthly options range from 1 to 9 months. Yearly options include 1, 2, 3, or 5 years. Note This option appears only when the billing method is Subscription.

Read and select the checkbox for Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start, and then click OK in the OK dialog box.
You can monitor the task progress on the data synchronization page.