Synchronize data from SLS to a ClickHouse cluster - Data Transmission Service

Prerequisites

The data to synchronize has been collected into an SLS Logstore. For more information, see Data collection.
A destination ApsaraDB for ClickHouse cluster has been created. For more information, see Create a cluster.
A database and a table have been created in the destination ApsaraDB for ClickHouse cluster to receive the data. For more information, see Create a database, Create a table, and Object naming conventions.
Note
- A Logstore in SLS corresponds to a database in an ApsaraDB for ClickHouse cluster, and a topic corresponds to a table.
- In an ApsaraDB for ClickHouse cluster, do not create columns for indexed fields from the Logstore that start with __ and end with __.

Usage notes

Type	Description
Source database limits	The data retention period of the source Logstore must be longer than 7 days.
Other limits	DTS serverless instances are not supported. Schema synchronization is not supported. You must manually create tables in the destination and add the required fields. For more information, see Table and field information. You cannot modify synchronization objects. Index fields that start with `__` and end with `__` cannot be synchronized. To synchronize data from all topics in a Logstore to a single table in an ApsaraDB for ClickHouse cluster, enter Table Name in the Table Name field when you configure synchronization objects. Otherwise, topics will be filtered out, causing data loss. Restarting a task may cause a small amount of data duplication. Each task performs both full and incremental synchronization. In the task list, these two phases are combined and displayed as a single incremental synchronization task. The number of databases to synchronize cannot exceed the ApsaraDB for ClickHouse limit of 256. During initial full data synchronization, DTS consumes read and write resources from the source and destination databases, increasing their load. Evaluate the performance of your databases and run the synchronization during off-peak hours, for example, when CPU utilization for both is below 30%. To prevent data inconsistencies, do not use other services to write to the destination database during DTS 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.

Billing

Synchronization type	Link configuration fees
Full data synchronization	Free of charge.
Incremental data synchronization	Charged. For more information, see billing overview.

Database account permissions

Database	Permissions	Creation and authorization
Destination ApsaraDB for ClickHouse cluster	Version 22.8 or later: Read and write permissions on the destination database. A privileged account has the required permissions. Version 21.8: Read, Write and Set Permissions and Enable DDL.	Account management for Community-compatible Edition clusters

Before you begin

Before you create a DTS instance, grant it permissions to read data from Simple Log Service. You can use the AccessKey pair of a RAM user or an STS token.

RAM user

Create a RAM user.
1. Go to the Users page in the RAM console.
2. In the upper-left corner of the page, click Create User.
3. Enter a User Login Name, and in the Access Configuration section, select Permanent AccessKey.
4. Click OK.
  
  Important
  After the RAM user is created, save the AccessKey ID and AccessKey secret.
Return to the Users page and find the RAM user you created.
In the Actions column for the target RAM user, click Add Permissions.
In the text box under Policy, search for and select the AliyunLogReadOnlyAccess policy.

Note
The AliyunLogReadOnlyAccess policy grants read-only permissions on Simple Log Service. A RAM user with this policy can access Simple Log Service. You can also create a custom policy as needed. For more information, see Create a custom policy.
Click Confirm Add Authorization.

STS token

Create a RAM user and grant permissions.
1. Go to the Users page in the RAM console.
  1. In the upper-left corner of the page, click Create User.
  2. Enter a User Login Name, and in the Access Configuration section, select Permanent AccessKey.
  3. Click OK.
    
    Important
    After the RAM user is created, save the AccessKey ID and AccessKey secret.
2. Return to the Users page and find the RAM user you created.
3. In the Actions column for the target RAM user, click Add Permissions.
4. In the text box under Policy, search for and select the AliyunSTSAssumeRoleAccess policy. This policy grants the RAM user permissions to call the AssumeRole operation of Security Token Service (STS).
5. Click Confirm Add Authorization.
Create a RAM role and grant permissions.
1. Go to the RAM Roles page.
2. In the upper-left corner of the page, click Create Role.
3. On the Create Role page, set Select Trusted Entity to Alibaba Cloud Account, specify the Alibaba Cloud Account, and then click OK.
4. Enter a Role Name and click OK.
5. On the role details page, click Add Permission. In the text box under Policy, search for and select the AliyunLogReadOnlyAccess policy.
  
  Note
  The AliyunLogReadOnlyAccess policy grants read-only permissions on Simple Log Service. This allows the role to access Simple Log Service. You can also create a custom policy as needed. For more information, see Create a custom policy.
Obtain the STS token.

To obtain the STS token, use the RAM user to call the AssumeRole - Obtain temporary security credentials for a role API operation.

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	Parameter	Description
N/A	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 SLS.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region of the source Simple Log Service project.
	Project	Select the source Simple Log Service project.
	Logstore	Select the source Simple Log Service Logstore.
	AccessKey ID and AccessKey Secret	Enter the AccessKey ID and AccessKey Secret of the RAM user, or the STS token, created in the "Before you begin" section.
	STS Token
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 ClickHouse.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region of the destination ApsaraDB for ClickHouse cluster.
	Replicate Data Across Alibaba Cloud Accounts	For this example, select No, as the database instance belongs to the current Alibaba Cloud account.
	Cluster Type	Select the type of the ApsaraDB for ClickHouse cluster.
	Cluster ID	Select the ID of the destination ApsaraDB for ClickHouse cluster.
	Database Account	Enter the database account for the destination ApsaraDB for ClickHouse cluster. For the required permissions, see Permission requirements for the database account.
	Database Password	Enter the password for the specified database account.

After you complete the configuration, click Test Connectivity and Proceed at the bottom of the page.
Note
Ensure that the IP address blocks of the DTS service are added to the security settings of the source and destination databases, either automatically or manually, to allow access from DTS servers. For more information, see Add the IP address whitelist of DTS servers.

Configure the task objects.

On the Configure Objects page, specify the objects to synchronize.

Parameter	Description
Synchronization Types	Both Full Data Synchronization and Incremental Data Synchronization are supported. After the precheck, DTS performs a full synchronization of the selected objects from the source to the destination, which serves as the baseline for subsequent incremental synchronization.
Processing Mode of Conflicting Tables	Precheck and Report Errors: Checks for tables with the same names in the destination database. If any tables with the same names are found, an error is reported during the precheck and the data synchronization task does not start. Otherwise, the precheck is successful. Note If you cannot delete or rename the table with the same name in the destination database, you can map it to a different name in the destination. For more information, see Object name mapping. Ignore Errors and Proceed: Skips the check for tables with the same name in the destination database. Warning Selecting Ignore Errors and Proceed may cause data inconsistency and put your business at risk. For example: If the table schemas are consistent and a record in the destination database has the same primary key or unique key value as a record in the source database: During full data synchronization, DTS retains the destination record and skips the source record. During incremental synchronization, DTS overwrites the destination record with the source record. If the table schemas are inconsistent, data initialization may fail. This can result in only partial data synchronization or a complete synchronization failure. Use with caution.
Capitalization of Object Names in Destination Instance	Configure the case-sensitivity policy for database, table, and column names in the destination instance. By default, the DTS default policy is selected. You can also choose to use the default policy of the source or destination database. For more information, see Case policy for destination object names.
Selected Objects	Specify the destination database. Hover over the Logstore that you want to synchronize in the Selected Objects section and click the Edit button that appears. In the Edit Schema dialog box, change the Schema Name to the name of the destination database in the ApsaraDB for ClickHouse cluster. Note By default, DTS maps the Logstore name to the database name of the target ClickHouse cluster. If the Logstore name contains a `-` character, this character is replaced with a `_`. Click OK. Specify the destination table. Next to Table, click Add Table. In the Add Table dialog box, configure the synchronization objects and destination tables. You can set the synchronization granularity to Logstore or Topic: Logstore granularity: In the Table Name text box, enter .. Important* .* represents all topics in the Logstore. You can only write data from all topics in a Logstore to the same table. Topic granularity: In the Table Name text box, enter the name of the topic to be synchronized from the Logstore. In the Destination Table Name text box, enter the name of the destination table in the ApsaraDB for ClickHouse cluster. Note If the granularity of the synchronization object is Logstore, do not click Add Table. If the synchronization granularity is Topic, click Add Table and map each topic to a table in the ApsaraDB for ClickHouse cluster. Click OK. Specify the destination columns. Note If the synchronization granularity is Topic, you need to repeat the following operations to map each topic to a table in the ApsaraDB for ClickHouse cluster. In the Selected Objects section, hover over the table that you just created and click the Edit button that appears. In the Edit Table dialog box, confirm the indexed fields (columns) to be synchronized. Note To exclude a field from synchronization, click the icon in the Actions column for that field. In the Destination Column Name text box, change the name to the destination column that will store the data from the corresponding indexed field. Optional: In the Destination Type column, select the data type for the corresponding column. Note For information about the default data type mappings in DTS, see Data type mappings. Optional: Configure non-indexed fields to be synchronized. Note You can repeat the following steps to configure the non-indexed fields that you want to synchronize. Click the icon to add and configure a new row. In the Column Name column, enter the name of the non-indexed field that you want to synchronize. In the Destination Column Name column, enter the name of the destination column in the ApsaraDB for ClickHouse cluster. Optional: In the Destination Type column, select the data type for the corresponding column. Note For information about the default data type mappings in DTS, see Data type mappings. After configuring all the fields to be synchronized, click Confirm.

Click Next: Advanced Settings.

Parameter	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.
Start Incremental Synchronization from Selected Offset	Specifies whether to start incremental synchronization from a specific point in time. For this example, keep the default setting of No. Note If you select Yes, you must also select the offset information from the drop-down list.
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).
Environment Tag	Select an environment tag to identify the instance based on your business requirements. No selection is needed in this example.
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.

Appendix

Data type mapping

SLS	ClickHouse cluster
TEXT	STRING
JSON	STRING
DOUBLE	FLOAT64
LONG	INT64

Table and field information

Table information

When you manually create a destination table, ensure that it meets the following requirements.

Important

The ENGINE of the destination table must be ENGINE = ReplicatedReplacingMergeTree(_version, _is_deleted) to prevent data inconsistency.

For a ClickHouse Community Edition instance, you must create a local table and a distributed table. The name of the distributed table must match the table name specified for the synchronization objects. The local table must be named <distributed_table_name>+_local.
For a ClickHouse Enterprise Edition instance, you must create a table with the same name specified for the synchronization objects.

Field information

In addition to the source fields, the destination table must contain the following fields. Run the SELECT * FROM table_name final WHERE _sign>0; statement to query data. The WHERE clause filters out deleted data, and the final keyword deduplicates rows based on the sorting key.

Version	Parameter	Type	Default	Description
ClickHouse Community Edition earlier than 23.8	_sign	Int8	1	The DML operation type. INSERT: The value is 1. UPDATE: The value is 1. DELETE: The value is -1.
ClickHouse Community Edition earlier than 23.8	_version	UInt64	1	The timestamp when the data is written to the ClickHouse cluster.
ClickHouse Enterprise Edition and ClickHouse Community Edition 23.8 and later	_sign	Int8	1	The DML operation type. INSERT: The value is 1. UPDATE: The value is 1. DELETE: The value is -1.
	_is_deleted	UInt8	0	Indicates whether the record is deleted. INSERT: The value is 0. DELETE: The value is 1. UPDATE: The value is 0.
	_version	UInt64	1	The timestamp when the data is written to the ClickHouse cluster.