ApsaraDB for ClickHouse is a columnar database management system (DBMS) designed for online analytical processing (OLAP). Compared with traditional analytical databases, ApsaraDB for ClickHouse delivers faster aggregate queries on large and wide tables. You can use Data Transmission Service (DTS) to synchronize data from a MySQL database (either a self-managed MySQL database or an ApsaraDB RDS for MySQL instance) to an ApsaraDB for ClickHouse cluster. The data synchronization feature enables efficient data transfer and analysis. This topic describes how to synchronize data from an ApsaraDB RDS for MySQL instance to an ApsaraDB for ClickHouse cluster.
Prerequisites
A destination ApsaraDB for ClickHouse cluster of version 20.8 or later is created. For more information, see Create a cluster.
The storage capacity of the ApsaraDB for ClickHouse cluster must be greater than the used storage space of the source ApsaraDB RDS for MySQL instance.
Limits
Type | Description |
Limits on source database |
|
Others |
|
Special cases |
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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 operations that can be synchronized
Operation type | SQL statements |
DML | INSERT, UPDATE, DELETE |
DDL |
|
Data type mappings
MySQL and ClickHouse clusters support different data types. The data types cannot be mapped one-to-one. During schema initialization, DTS maps the data types based on the data types that are supported by the destination database. For more information, see Data type mappings for schema initialization.
Permissions required for database accounts
Database | Required permissions | Creation and authorization methods |
Source ApsaraDB RDS for MySQL | Read permissions on the objects to synchronize. | |
Destination ApsaraDB for ClickHouse cluster |
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If the source database account that you use is not created and authorized by using the ApsaraDB RDS for MySQL console, make sure that the account has the REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions.
Procedure
Use one of the following methods to go to the Data Synchronization page and select the region in which the data synchronization instance resides.
DTS console
Log on to the DTS console.
In the left-side navigation pane, click Data Synchronization.
In the upper-left corner of the page, select the region in which the data synchronization instance resides.
DMS console
NoteThe 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.
Log on to the DMS console.
In the top navigation bar, move the pointer over Data + AI and choose
.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
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 Existing Connection
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.
NoteIn the DTS console, register a database with DTS on the Database Connections page or the new configuration page. For more information, see Manage database connections.
In the DMS console, you can select an existing database from the Select a DMS database instance. drop-down list. You can also click Add DMS Database Instance or go back to the homepage of the DMS console to register a database with DMS. For more information, see Register an Alibaba Cloud database instance and Register a database hosted on a third-party cloud service or a self-managed database.
Database Type
Select MySQL.
Access Method
Select Alibaba Cloud Instance.
Instance Region
Select the region where the source ApsaraDB RDS for MySQL instance resides.
Replicate Data Across Alibaba Cloud Accounts
In this example, the source and destination instances belong to the same Alibaba Cloud account. Select No.
RDS Instance ID
Select the ID of the source ApsaraDB RDS for MySQL instance.
Database Account
Enter the database account of the source ApsaraDB RDS for MySQL instance. For information about the permissions that are required for the account, see Permissions required for database accounts.
Database Password
The password that is used to access the database.
Encryption
Specifies whether to encrypt the connection to the database. You can select Non-encrypted or SSL-encrypted based on your business requirements. If you want to set this parameter to SSL-encrypted, you must enable SSL encryption for the ApsaraDB RDS for MySQL instance before you configure the DTS task. For more information, see Use a cloud certificate to enable SSL encryption.
Destination Database
Select Existing Connection
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.
NoteIn the DTS console, register a database with DTS on the Database Connections page or the new configuration page. For more information, see Manage database connections.
In the DMS console, you can select an existing database from the Select a DMS database instance. drop-down list. You can also click Add DMS Database Instance or go back to the homepage of the DMS console to register a database with DMS. For more information, see Register an Alibaba Cloud database instance and Register a database hosted on a third-party cloud service or a self-managed database.
Database Type
Select ClickHouse.
Access Method
Select Alibaba Cloud Instance.
Instance Region
Select the region where the destination ApsaraDB for ClickHouse cluster resides.
Replicate Data Across Alibaba Cloud Accounts
In this example, the source and destination instances belong to the same Alibaba Cloud account. Select No.
Cluster Type
Select the type of the ApsaraDB for ClickHouse cluster based on your business requirements.
Cluster ID
Select the ID of the destination ApsaraDB for ClickHouse cluster.
Database Account
Enter the database account of the destination ApsaraDB for ClickHouse cluster. For information about the permissions that are required for the account, see Permissions required for database accounts.
Database Password
The password that is used to access the database.
Click Test Connectivity and Proceed in the lower part of the page.
NoteMake 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 the CIDR blocks of DTS servers.
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.
Parameter
Description
Synchronization Types
The synchronization types. By default, Incremental Data Synchronization is selected. You must also select Schema Synchronization and Full Data Synchronization. After the precheck is complete, DTS synchronizes the historical data of the selected objects from the source database to the destination cluster. The historical data is the basis for subsequent incremental synchronization.
Processing Mode of Conflicting Tables
Precheck and Report Errors: checks whether the destination database contains tables that have 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 synchronization task cannot be started.
NoteIf 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 synchronized 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.
WarningIf you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to potential risks.
If the source and destination databases have the same schema and a data record in the destination database has the same primary key value or unique key value as a data record in the source database:
During full data synchronization, DTS does not synchronize the data record to the destination database. The existing data record in the destination database is retained.
During incremental data synchronization, DTS synchronizes 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, data may fail to be initialized. In this case, only some columns are synchronized, or the data synchronization 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 ensure that the capitalization of object names is consistent with that in 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 and click the
icon to add the objects to the Selected Objects section.
NoteYou can select databases, tables, or columns as the objects to be synchronized.
Selected Objects
To rename an object that you want to synchronize to the destination instance, right-click the object in the Selected Objects section. For more information, see the "Map the name of a single object" section of the Map object names topic.
To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see the "Map multiple object names at a time" section of the Map object names topic.
NoteTo configure filter conditions for a table, right-click the table in the Selected Objects section. In the dialog box that appears, configure filter conditions. For more information, see Configure filter conditions.
If you use the object name mapping feature to rename an object, other objects that depend on the object may fail to be synchronized.
Click Next: Advanced Settings to configure advanced settings.
Parameter
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 tasks, purchase a dedicated cluster. For more information, see What is a DTS dedicated cluster.
Time zone of destination database
You can select the time zone for the DateTime data that is written to the ApsaraDB for ClickHouse cluster based on your business requirements.
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.
NoteIf 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.
ImportantThe 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
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.
NoteThis parameter is displayed 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.
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
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, no environment tag is selected.
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 task. 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.
Click Next: Configure Database and Table Fields to configure the Type, Primary Key Column, Sort Key, Distribution Key, and Partition Key for the tables to be synchronized in the ApsaraDB for ClickHouse cluster.
NoteDTS configures a set of data by default. You can select All from the Definition Status drop-down list and modify the data.
The Primary Key Column and Sort Key can be composite keys. You can select multiple fields from the corresponding drop-down list as the Primary Key Column or Sort Key. You must select one or more columns from the Primary Key Column as the Partition Key. You can select only one field as the Distribution Key. For more information about primary key columns, sort keys, and partition keys, see CREATE TABLE.
You can leave the Partition Key unspecified. However, you cannot select a nullable field as a partition key. Otherwise, the synchronization task fails.
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.
NoteBefore 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 an 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 instance. 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.
NoteThis 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.
Appendices
Time information
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 |
Table and field information
Table information
If you do not use the object name mapping feature, the tables that you create must meet the following requirements.
If the destination table contains the ENGINE parameter, the parameter must be set to ENGINE = ReplicatedReplacingMergeTree(_version, _is_deleted)
. Otherwise, data inconsistency may occur.
ApsaraDB for ClickHouse Community Edition instance: You must create a local table and a distributed table. The name of the distributed table must be the same as the name of the source table. The name of the local table must be
<Name of the distributed table>
+_local
.ApsaraDB for ClickHouse Enterprise Edition instance: You must create a table that has the same name as the source table.
Field information
You can use the select * from table_name final where _sign>0;
statement to query data in a ClickHouse instance. The where condition filters deleted data, and the final field after the table name filters data with the same sort key.
Version | Name | Data type | Default value | Description |
Community Edition earlier than version 23.8Community Edition | _sign | Int8 | 1 | The type of the DML operation.
|
_version | UInt64 | 1 | The timestamp when the data is written to ApsaraDB for ClickHouse. | |
Enterprise Edition and Community Edition 23.8 and later | _sign | Int8 | 1 | The type of the DML operation.
|
_is_deleted | Int8 | 0 | Indicates whether the record is deleted:
| |
_version | UInt64 | 1 | The timestamp when the data is written to ApsaraDB for ClickHouse. |