All Products
Search
Document Center

Data Transmission Service:Synchronize data from an ApsaraDB RDS for MySQL instance to an ApsaraDB for ClickHouse cluster

Last Updated:Sep 06, 2024

ApsaraDB for ClickHouse is a column-oriented database management system (DBMS) for online analytical processing (OLAP) of queries. ApsaraDB for ClickHouse provides aggregate queries on wide tables with a speed that is one order of magnitude faster than other analytical databases. You can use Data Transmission Service (DTS) to synchronize data from a MySQL database, such as a self-managed MySQL database or an ApsaraDB RDS for MySQL instance, to an ApsaraDB for ClickHouse cluster. This way, you can transfer and analyze data with ease. This topic describes how to synchronize data from an ApsaraDB RDS for MySQL instance to an ApsaraDB for ClickHouse cluster.

Prerequisites

  • An ApsaraDB for ClickHouse cluster of V20.8 or later 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 the data in the source ApsaraDB 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 specify the same name for the database in the destination ApsaraDB for ClickHouse cluster as the database that stores the data to be synchronized in the source ApsaraDB RDS for MySQL instance. Otherwise, you must use the name mapping feature to map the name of the source database to the name of the destination database in the Selected Objects section in the Configure Objects and Advanced Settings step. For more information, see Map object names.

Usage notes

Category

Description

Limits on the source database

  • The tables to be synchronized from the source database must contain primary keys.

  • If you select tables as the objects to be synchronized and you need to modify the tables, such as renaming tables or columns, you can synchronize up to 1,000 tables in a single data synchronization task. If you run a task to synchronize more than 1,000 tables, a request error occurs. In this case, we recommend that you split the tables and configure multiple tasks to synchronize the tables in batches or configure a task to synchronize the entire database.

  • The following requirements for binary logs must be met:

    • By default, the binary logging feature is enabled for an ApsaraDB RDS for MySQL instance. Make sure that the binlog_row_image parameter is set to full. Otherwise, error messages are returned during precheck and the data synchronization task cannot be started. For more information, 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 at least seven days. Otherwise, the data synchronization task may fail because DTS cannot obtain the binary logs. In exceptional circumstances, data inconsistency or loss may occur. Make sure that you configure the retention period of binary logs based on the preceding requirements. Otherwise, the service reliability or performance stated in the Service Level Agreement (SLA) of DTS may not be guaranteed. For more information about how to manage the binary log files of an ApsaraDB RDS for MySQL instance, see Manage binary log files.

  • During schema synchronization and full data synchronization, do not execute DDL statements to change the schemas of databases or tables. Otherwise, the data synchronization task fails.

Other limits

  • If the DDL statements that are executed on the source ApsaraDB RDS for MySQL instance do not comply with the standard MySQL syntax, a synchronization task may fail or data may be lost.

  • RENAME TABLE operations cannot be synchronized.

  • The DATETIME data in the source ApsaraDB RDS for MySQL instance must be in the time ranges supported by the destination ApsaraDB for ClickHouse cluster. Otherwise, data inconsistency between the source and destination databases occurs. For more information, see the Time ranges section of this topic.

  • All selected columns of the Partition Key parameter must be non-empty fields. Otherwise, a synchronization task fails.

  • Up to 256 databases can be synchronized to an ApsaraDB for ClickHouse cluster.

  • The names of the databases, tables, and columns to be synchronized must comply with the naming conventions of ApsaraDB for ClickHouse. For more information, see the Limits on object naming conventions section of the Limits topic.

  • During schema synchronization, DTS automatically adds the _version field and the _sign or is_deleted field to destination tables. If you do not select Schema Synchronization for the Synchronization Types parameter when you configure the data synchronization task, you must manually create tables to receive data in the destination database and add additional fields to the tables. For more information, see the Tables and fields section of this topic.

  • Before you synchronize data, evaluate the impact of data synchronization on the performance of the source and destination databases. We recommend that you synchronize data during off-peak hours. During full data synchronization, DTS uses read and write resources of the source and destination databases. This may increase the loads on the database servers.

  • If you select one or more tables instead of an entire database as the objects to be synchronized, do not use tools such as pt-online-schema-change to perform DDL operations on the tables during data synchronization. Otherwise, data may fail to be synchronized.

    You can use Data Management (DMS) to perform online DDL operations. For more information, see Perform lock-free DDL operations.

  • Data inconsistency between the source and destination databases occurs if data from other sources is written to the destination database during data synchronization.

  • If the source database is an ApsaraDB RDS for MySQL instance for which the EncDB feature is enabled, full data synchronization cannot be performed.

Special cases

  • If the source database is a self-managed MySQL database, take note of the following items:

    • If you perform a primary/secondary switchover on the source database when the data synchronization task is running, the task fails.

    • DTS calculates synchronization latency based on the timestamp of the latest synchronized data in the destination database and the current timestamp in the source database. If no DML operation is performed on the source database for a long time, the synchronization latency may be inaccurate. If the latency of the data synchronization 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 synchronized, you can create a heartbeat table. The heartbeat table is updated or receives data every second.

    • DTS executes the CREATE DATABASE IF NOT EXISTS 'test' statement in the source database as scheduled to move forward the binary log file position.

  • If the source database is an Apsara RDS for MySQL instance, take note of the following item:

    An ApsaraDB RDS for MySQL instance that does not record transaction logs, such as a read-only ApsaraDB RDS for MySQL 5.6 instance, cannot be used as the source database.

Billing

Synchronization typeTask configuration fee
Schema synchronization and full data synchronizationFree of charge.
Incremental data synchronizationCharged. For more information, see Billing overview.

SQL operations that can be synchronized

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. During initial schema synchronization, DTS establishes mappings between source fields and destination fields based on the data types supported by the destination database. For more information, see Data type mappings for schema synchronization.

Permissions required for database accounts

Database type

Required permissions

References

Source ApsaraDB RDS for MySQL instance

Read permissions on the objects to be synchronized.

Create an account and Modify the permissions of an account

Destination ApsaraDB for ClickHouse cluster

  • ApsaraDB for ClickHouse cluster that runs ClickHouse V22.8 or later: read and write permissions on the destination database. A privileged account has the required requirements.

  • ApsaraDB for ClickHouse cluster that runs ClickHouse V21.8: Read, Write and Set Permissions and Enable DDL.

Manage database accounts of an ApsaraDB for ClickHouse cluster

Note

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

  1. Go to the Data Synchronization Tasks page.

    1. Log on to the DMS console.

    2. In the top navigation bar, move the pointer over DTS.

    3. Choose DTS (DTS) > Data Synchronization.

    Note
  2. On the right side of Data Synchronization Tasks, select the region in which the data synchronization instance resides.

    Note

    If you use the new DTS console, select the region in which you want to create the data synchronization task in the top navigation bar.

  3. Click Create Task. On the Create Task page, configure the source and destination databases. The following table describes the parameters.

    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 instance that you want to use. You can choose whether to use an existing instance based on your business requirements.

    • If you select an existing instance, DTS automatically populates the parameters for the database.

    • If you do not select an existing instance, you must manually configure parameters for the database.

    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 data is synchronized 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 instance.

    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 instance that you want to use. You can choose whether to use an existing instance based on your business requirements.

    • If you select an existing instance, DTS automatically populates the parameters for the database.

    • If you do not select an existing instance, you must manually configure parameters for the database.

    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 data is synchronized 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 database account, see the Permissions required for database accounts section of this topic.

    Database Password

    The password that is used to access the database instance.

  4. 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 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 database is deployed 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 whitelist of the database to allow DTS to access the database. For more information, see Add the CIDR blocks of DTS servers.

    Warning

    If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database or instance, or to the ECS security group rules, security risks may arise. Therefore, before you use DTS to synchronize 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 ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

  5. Configure the objects to be synchronized and advanced settings. The following table describes the parameters.

    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.

      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 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.

      Warning

      If 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 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 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 向右 icon to add the objects to the Selected Objects section.

    Note

    You can select columns, tables, and databases 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.

    Note
    • To specify filter conditions to synchronize data that meets the specified conditions, right-click the table to be synchronized in the Selected Objects section. In the dialog box that appears, enter one or more SQL conditions. For more information, see Specify filter conditions.

    • If you use the object name mapping feature to rename the database or collection to which the data is synchronized, other objects that depend on the database or collection may fail to be synchronized.

  6. Click Next: Advanced Settings to configure advanced settings.

    Parameter

    Description

    Dedicated Cluster for Task Scheduling

    By default, DTS schedules tasks to shared clusters. You do not need to configure this parameter. 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 synchronization task. If the task fails or the synchronization latency exceeds the specified threshold, alert contacts will receive notifications. Valid values:

    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 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.

    Note

    This 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.

    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:

    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.

    • Yes: does not write SQL operations on heartbeat tables. In this case, 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.

  7. Click Next: Configure Database and Table Fields, and then configure the Type, Primary Key Column, Sort Key, Distribution Key, and Partition Key parameters of the destination table in the ApsaraDB for ClickHouse cluster.

    Note
    • By default, these parameters are configured by DTS. To modify the parameters, set the Definition Status parameter to All.

    • Primary Key Column and Sort Key can be composite keys. 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, see CREATE TABLE.

    • The Partition Key parameter is optional. However, if you configure this parameter, all selected columns of the Partition Key parameter must be non-empty fields. Otherwise, the synchronization task fails.

  8. 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.

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

  10. 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.

    Note

    This parameter is available only if you select the Subscription billing method.

  11. Read and select the Data Transmission Service (Pay-as-you-go) Service Terms.

  12. Click Buy and Start. In the dialog box that appears, click OK.

    You can view the progress of the task in the task list.

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.