Migrate data from an ApsaraDB RDS for MySQL instance to an ApsaraDB for ClickHouse cluster - Data Transmission Service

Data Transmission Service (DTS) allows you to migrate data from a MySQL database, such as a self-managed MySQL database or an ApsaraDB RDS for MySQL database to an ApsaraDB for ClickHouse cluster. This helps you analyze business data in a centralized manner. This topic describes how to migrate data from an ApsaraDB RDS for MySQL instance to an ApsaraDB for ClickHouse cluster.

Prerequisites

The destination ApsaraDB for ClickHouse cluster is created. For more information, see Create an ApsaraDB for ClickHouse cluster.
Note
The available storage space of the destination ApsaraDB for ClickHouse cluster is larger than the total size of data in the source RDS for MySQL instance.
A database is created in the destination ApsaraDB for ClickHouse cluster to receive data. For more information, see Create a database.
Important
We recommend that you create a database in the ApsaraDB for ClickHouse cluster with the same name as the database to which the data to be migrated belongs in the source ApsaraDB RDS for MySQL instance. Otherwise, you must use the object name mapping feature in the Selected Objects section in the Configure Objects and Advanced Settings step. For more information, see Map object names.

Limits

Category	Description
Limits on the source database	If you select tables as the objects to be migrated and you want to modify the tables in the destination database, such as renaming tables or columns, you can migrate up to 1,000 tables in a single data migration task. If you run a task to migrate more than 1,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to migrate the tables or configure a task to migrate the entire database. The following requirements for binary logs must be met: By default, the binary logging feature is enabled. The value of the binlog_row_image parameter is set to full. Otherwise, error messages are returned during the precheck and the data migration task cannot be started. For more information about parameter configurations, see Modify instance parameters. Important If the source database is a self-managed MySQL database, you must enable the binary logging feature and set the binlog_format parameter to row and the binlog_row_image parameter to full. If the source database is a self-managed MySQL database deployed in a dual-primary cluster, you must set the log_slave_updates parameter to ON. This ensures that DTS can obtain all binary logs. For more information, see Create an account for a self-managed MySQL database and configure binary logging. The binary logs of the source database must be stored for more than seven days. Otherwise, DTS may fail to obtain the binary logs, which may cause the task to fail, or even data inconsistency and data loss. Make sure that you configure the retention period of binary logs based on the preceding requirements. Otherwise, the service level agreement (SLA) of DTS does not guarantee service reliability or performance. For more information about how to manage the binary log files of an ApsaraDB RDS for MySQL instance, see Manage binary log files.
Other limits	The DDL statements in the destination database must be standard. Otherwise, the data migration task may fail or data loss may occur. The RENAME TABLE statement cannot be migrated. The data of the DateTime type in an ApsaraDB for ClickHouse cluster is in the range of 1970-01-01 00:00:00 to 2106-02-07 06:28:15. If the time data in the ApsaraDB RDS for MySQL instance is not within this range, the data of the DateTime type that is migrated to the destination ApsaraDB for ClickHouse cluster may be incorrect. The Partition Key cannot be an empty field. Otherwise, the data migration task fails. The number of databases to be migrated to the destination ApsaraDB for ClickHouse cluster cannot exceed 256. The names of the databases, tables, and columns that you want to migrate must comply with the naming conventions of ApsaraDB for ClickHouse. For more information, see the "Object naming conventions" section of the Limits topic. If you migrate data to an ApsaraDB for ClickHouse Community-compatible Edition cluster, DTS automatically adds the _version field and the _sign or _is_deleted field to destination tables. If you migrate data to an ApsaraDB for ClickHouse Enterprise Edition cluster, DTS does not add fields. Note During incremental data migration, DTS records the timestamp that is generated when data is written to the destination ApsaraDB for ClickHouse Community-compatible Edition cluster in the _version field and the types of DDL statements in the _sign field. The INSERT and UPDATE statements are recorded as 1, and the DELETE statements are recorded as -1. Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. During initial full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads on the database servers. If you migrate one or more tables other than the entire database to the destination database, do not use tools such as pt-online-schema-change to perform online DDL operations on the objects to be migrated. Otherwise, the data migration task fails. You can use Data Management (DMS) to perform online DDL operations. For more information, see Perform lock-free DDL operations. If you use tools other than DTS to write data to the destination database, data inconsistency between the source and destination databases may occur.
Precautions	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 an extended period of 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 regularly executes the CREATE DATABASE IF NOT EXISTS `test` statement in the source database to move forward the binary log file position.

Billing

Migration type	Instance configuration fee	Internet traffic fee
Schema migration and full data migration	Free of charge.	Free of charge.
Incremental data migration	Charged. For more information, see Billing overview.	Free of charge.

SQL operations that can be migrated during incremental migration

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE
DDL	CREATE TABLE TRUNCATE TABLE ALTER TABLE ADD COLUMN MODIFY COLUMN DROP TABLE and DROP COLUMN

Data type mappings

The data types supported by ApsaraDB RDS for MySQL instances and ApsaraDB for ClickHouse clusters do not have one-to-one correspondence. Therefore, DTS converts the data types of the source database to those of the destination database during schema synchronization. For more information, see Data type mappings between heterogeneous databases.

Permissions required for database accounts

Database	Required permission	References
Source ApsaraDB RDS for MySQL instance	Read permissions on the objects to be migrated	Create an account and Modify the permissions of an account.
Destination ApsaraDB for ClickHouse cluster	ApsaraDB for ClickHouse V22.8: the read and write permissions on the destination database. In this case, you can use a privileged account. ApsaraDB for ClickHouse V21.8: the read, write, and set permissions and the permissions to enable DDL operations.	Manage database accounts of an ApsaraDB for ClickHouse cluster

Note

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

Procedure

Go to the Data Migration Tasks page.
1. Log on to the Data Management (DMS) console.
2. In the top navigation bar, move the pointer over DTS.
3. Choose DTS (DTS) > Data Migration.
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.
- You can also go to the Data Migration page of the new DTS console.
From the drop-down list on the right side of Data Migration Tasks, select the region in which your data migration instance resides.
Note
If you use the new DTS console, you must select the region in which the data migration instance resides in the upper-left corner.

Click Create Task. On the Create Task wizard page, configure the source and destination databases.

Section	Parameter	Description
N/A	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 an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	The database that you want to use. You can choose whether to use an existing database based on your business requirements. If you select an existing database, DTS automatically populates the parameters for the database. If you do not select an existing database, you must configure the following database information.
	Database Type	The type of the source database. Select MySQL.
	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source ApsaraDB RDS for MySQL instance resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
	RDS Instance ID	The ID of the source ApsaraDB RDS for MySQL instance.
	Database Account	The database account of the source ApsaraDB RDS for MySQL instance. For information about the permissions that are required for the account, see the Permissions required for database accounts section of this topic.
	Database Password	The password 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 an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	The database that you want to use. You can choose whether to use an existing database based on your business requirements. If you select an existing database, DTS automatically populates the parameters for the database. If you do not select an existing database, you must configure the following database information.
	Database Type	The type of the destination database. Select ClickHouse.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination ApsaraDB for ClickHouse cluster resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
	Cluster Type	The type of the destination ApsaraDB for ClickHouse cluster.
	Cluster ID	The ID of the destination ApsaraDB for ClickHouse cluster.
	Database Account	The database account of the destination ApsaraDB for ClickHouse cluster. For information about the permissions that are required for the account, see the Permissions required for database accounts section of this topic.
	Database Password	The password that is used to access the database.

In the lower part of the page, click Test Connectivity and Proceed.
If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the IP address whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance, and you must make sure that the ECS instance can access the database. If the self-managed database is hosted on multiple ECS instances, you must manually add the CIDR blocks of DTS servers to the security group rules of each ECS instance. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the IP address whitelist of the database to allow DTS to access the database. For more information, see the CIDR blocks of DTS servers section of the Add the CIDR blocks of DTS servers topic.
Warning
If the public CIDR blocks of DTS servers are automatically or manually added to the whitelist of a database instance or to the security group rules of an ECS instance, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or security group rules and forbidding unauthorized CIDR blocks, or connecting the database instance to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

Configure the objects to be migrated and advanced settings.

Parameter	Description
Migration Types	To perform only full data migration, select Schema Migration and Full Data Migration. To ensure service continuity during data migration, select Schema Migration, 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 contains tables that use the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started. Note If the source and destination databases contain tables with identical names and the tables in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the tables that are migrated to the destination database. For more information, see Map object names. Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to the following potential risks: If the source and destination databases have the same schema, and a data record has the same primary key as an existing data record in the destination database, the following scenarios may occur: During full data migration, DTS does not migrate the data record to the destination database. The existing data record in the destination database is retained. During incremental data migration, DTS migrates the data record to the destination database. The existing data record in the destination database is overwritten. If the source and destination databases have different schemas, only specific columns are migrated or the data migration task fails. Proceed with caution.
Capitalization of Object Names in Destination Instance	The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. 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 Select columns, tables, or databases as the objects to be migrated.
Selected Objects	To rename an object that you want to migrate to the destination instance, right-click the object in the Selected Objects section. For more information, see Map the name of a single object. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time. Note To filter data, right-click the table that you want to migrate in the Selected Objects section. In the dialog box that appears, set filter conditions. For more information, see the Specify filter conditions. If you use the object name mapping feature to rename the database or collection to which the data is migrated, other objects that are dependent on the database or collection may fail to be migrated.

Click Next: Advanced Settings to configure advanced settings.

Parameter	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.
Set Alerts	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.
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 1440. 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	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements. In this example, you do not need to configure this parameter.
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.

Click Next: Configure Database and Table Fields. In the dialog box that appears, configure the Type, Primary Key Column, Sort Key, Distribution Key, and Partition Key parameters for the table that is migrated.
Note
- By default, the parameters are configured by DTS. To modify the parameters, set the Definition Status parameter to All.
- You can select multiple columns for the Primary Key Column or Sort Key parameter from the corresponding drop-down list. One or more columns specified for the Primary Key Column parameter can be selected for the Partition Key parameter. You can select only one column for the Distribution Key parameter. For more information about primary key, sort key, and partition key, see CREATE TABLE.
- You can leave the Partition Key parameter empty, but you cannot select a field that contains no data for this parameter. Otherwise, the data migration task fails.
Save the task settings and run a precheck.
1. 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.
2. 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
1. 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.
2. 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.
3. 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.
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.

Appendix

Time ranges

Data type	Minimum value	Maximum value
Date	1970-01-01 00:00:00	2149-06-06 00:00:00
Date32	1925-01-01 00:00:00	2283-11-11 00:00:00
DateTime	1970-01-01 08:00:00	2106-02-07 14:28:15
DateTime64	1925-01-01 08:00:00	2283-11-12 07:59:59

Tables and fields

Tables

If you do not use the object name mapping feature, make sure that the tables you create meet the following requirements:

If the destination database is an ApsaraDB for ClickHouse Community-compatible Edition cluster, you must create a local table and a distributed table. The name of the distributed table must be the same as that of the source table. The name of the local table is in the <Distributed table name>_local format.
If the destination database is an ApsaraDB for ClickHouse Enterprise Edition cluster, you must create a table with the same name as the source table.

Fields

Note

If the destination database is an ApsaraDB for ClickHouse Community-compatible Edition cluster that runs ClickHouse V23.8 or earlier, you can execute the select * from table_name final where _sign>0; statement to query data. In this statement, the WHERE clause can be used to filter the deleted data, and the final field behind the table name can be used to filter the data with the same sort keys.
If the destination database is an ApsaraDB for ClickHouse Enterprise Edition cluster or an ApsaraDB for ClickHouse Community-compatible Edition cluster that runs CLickHouse V23.8 or later, you can execute the corresponding SQL statement to query data. To filter data with the same sort keys, add the final field behind the table name.

Database edition and version	Field	Data type	Default value	Description
ApsaraDB for ClickHouse Community-compatible Edition cluster that runs ClickHouse V23.8 or earlier	_sign	Int8	1	The type of the DML operation. Valid values: 1: INSERT operation. 1: UPDATE operation. -1: DELETE operation.
	_version	UInt64	1	The time when data is written to the ClickHouse cluster.
ApsaraDB for ClickHouse Enterprise Edition cluster or ApsaraDB for ClickHouse Community-compatible Edition cluster that runs CLickHouse V23.8 or later	_is_deleted	Int8	0	Specifies whether the data record is deleted. Valid values: 0: The data record is inserted. 1: The data record is deleted. 0: The data record is updated.
	_version	UInt64	1	The time when data is written to the ClickHouse cluster.