Synchronize data from a PolarDB-X 1.0 instance to an ApsaraMQ for Kafka instance - Data Transmission Service

This topic describes how to synchronize data from a PolarDB-X 1.0 instance to an ApsaraMQ for Kafka instance by using Data Transmission Service (DTS).

Prerequisites

The source PolarDB-X 1.0 instance is created. For more information, see Create a PolarDB-X 1.0 instance.
In the destination ApsaraMQ for Kafka instance, a topic is created to receive the synchronized data. For more information, see Overview.
The available storage space of the destination ApsaraMQ for Kafka instance is larger than the total size of the data in the source PolarDB-X 1.0 instance.

Limits

Category	Description
Limits on the source database	The tables to be synchronized must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records. The tables that only have UNIQUE constraints do not support schema synchronization. Therefore, we recommend that you synchronize the tables that have PRIMARY KEY constraints. Tables that have secondary indexes cannot be synchronized. If you select tables as the objects to be synchronized and you want to edit the tables (such as renaming tables or columns) in the destination database, you can synchronize up to 5,000 tables in a single data synchronization task. If you run a task to synchronize more than 5,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to synchronize the tables in batches or configure a task to synchronize the entire database. The following requirements for binary logs of the ApsaraDB RDS for MySQL instances attached to the PolarDB-X 1.0 instance must be met: 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 synchronization task cannot be started. For an incremental data synchronization task, the binary logs of the source database must be retained for at least 24 hours. For a full and incremental data synchronization task, the binary logs of the source database must be retained for at least seven days. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data may be inconsistent or lost. After full data synchronization is complete, you can set the retention period to more than 24 hours. Make sure that you set the retention period of binary logs in accordance with the preceding requirements. Otherwise, the service reliability and performance stated in the Service Level Agreement (SLA) of DTS cannot be achieved. Limits on operations to be performed on the source database: If you change the network type of the PolarDB-X 1.0 instance during data synchronization, you must modify the network connection information of the data synchronization task after you change the network type. During data synchronization, do not upgrade or downgrade the ApsaraDB RDS for MySQL instances that are attached to the source instance, change the distribution of physical databases and tables that correspond to the logical databases and tables in the ApsaraDB RDS for MySQL instances, change shard keys, or perform DDL operations on source objects. Otherwise, the data synchronization task fails or data inconsistency occurs. During full data synchronization and incremental data synchronization, DTS temporarily disables the constraint check and cascade operations on foreign keys at the session level. If you perform the cascade update and delete operations on the source database during data synchronization, data inconsistency may occur. If you change the network type of the PolarDB-X 1.0 instance during data synchronization, you must also modify the network connection information of the data synchronization task. If you perform only full data synchronization, do not write data to the source database during data synchronization. Otherwise, data inconsistency may occur between the source and destination databases. To ensure data consistency, we recommend that you select schema synchronization, full data synchronization, and incremental data synchronization as the synchronization types.
Other limits	Data synchronization from a PolarDB-X 1.0 instance is distributed synchronization. You can configure only one data synchronization subtask for each ApsaraDB RDS for MySQL instance that is attached to the PolarDB-X 1.0 instance. You can query the status of each subtask in the task topology. If the destination ApsaraMQ for Kafka instance is upgraded or downgraded during data synchronization, you must restart the instance. 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 initial full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the loads on the database servers. During initial full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data synchronization is complete, the size of used tablespace of the destination database is larger than that of the source database. We recommend that you do not use gh-ost or pt-online-schema-change to perform DDL operations on objects to be synchronized. Otherwise, data synchronization may fail. During data synchronization, we recommend that you use only DTS to write data to the destination database. This prevents data inconsistency between the source and destination databases. If you use tools other than DTS to write data to the destination database, data loss may occur in the destination database when you use DMS to perform online DDL operations.

Supported synchronization topologies

One-way one-to-one synchronization
One-way one-to-many synchronization
One-way cascade synchronization
One-way many-to-one synchronization

For more information about the synchronization topologies that are supported by DTS, see Synchronization topologies.

SQL operations that can be synchronized

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE

Permissions required for database accounts

Database	Required permission	References
Source PolarDB-X 1.0 instance	The read permissions on the objects to be synchronized.	Manage accounts

Procedure

Go to the Data Synchronization page of the new DTS console.
Note
You can also log on to the Data Management (DMS) console. In the top navigation bar, click DTS. In the left-side navigation pane, choose DTS (DTS) > Data Synchronization.
In the upper-left corner of the page, select the region in which you want to create the data synchronization task.

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

Category	Parameter	Description
N/A	Task Name	The name of the task. DTS automatically assigns a name to the task. 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	The database instance that you want to use. You can choose whether to select 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 PolarDB-X 1.0.
	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source PolarDB-X 1.0 instance resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to synchronize data across Alibaba Cloud accounts. In this example, No is selected.
	Instance ID	The ID of the source PolarDB-X 1.0 instance.
	Database Account	The database account of the source PolarDB-X 1.0 instance. For more 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 of the database account.
Destination Database	Select an existing DMS database instance	The database instance that you want to use. You can choose whether to select 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 Kafka.
	Access Method	The access method of the destination database. Select Express Connect, VPN Gateway, or Smart Access Gateway. Note Alibaba Cloud Instance is not supported.
	Instance Region	The region in which the destination ApsaraMQ for Kafka instance resides.
	Connected VPC	The ID of the virtual private cloud (VPC) to which the destination ApsaraMQ for Kafka instance belongs. To obtain the VPC ID, perform the following operations: Log on to the ApsaraMQ for Kafka console and go to the Instance Details page of the ApsaraMQ for Kafka instance. In the Configuration Information section of the Instance Information tab, view the VPC ID.
	IP Address or Domain Name	An IP address of the destination ApsaraMQ for Kafka instance. Note To obtain an IP address of the ApsaraMQ for Kafka instance, perform the following operations: Log on to the ApsaraMQ for Kafka console and go to the Instance Details page of the ApsaraMQ for Kafka instance. In the Endpoint Information section of the Instance Information tab, obtain an IP address from the Default Endpoint parameter.
	Port Number	The service port number of the destination ApsaraMQ for Kafka instance. Default value: 9092.
	Database Account	The database account of the destination ApsaraMQ for Kafka instance. Note The database account and database password are required only for ApsaraMQ for Kafka instances for which the access control list (ACL) feature is enabled. For more information about how to enable the ACL feature, see Grant permissions to SASL users.
	Database Password
	Kafka Version	The version of the destination ApsaraMQ for Kafka instance.
	Encryption	Specifies whether to encrypt the connection to the destination instance. Select Non-encrypted or SCRAM-SHA-256 based on your business and security requirements.
	Topic	The topic that is used to receive the synchronized data. Select a topic from the drop-down list.
	Topic That Stores DDL Information	The topic that is used to store the DDL information. Select a topic from the drop-down list. If you do not specify this parameter, the DDL information is stored in the topic that is specified by the Topic parameter.
	Use Kafka Schema Registry	Specifies whether to use Kafka Schema Registry. Kafka Schema Registry provides a serving layer for your metadata. It provides a RESTful API to store and retrieve your Avro schemas. Valid values: No: does not use Kafka Schema Registry. Yes: uses Kafka Schema Registry. In this case, you must enter the URL or IP address that is registered in Kafka Schema Registry for your Avro schemas.

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 ensure that the ECS instance can access the database. 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 to the security settings of on-premises databases.
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.

Select the objects to be synchronized for the task and configure advanced settings.

Parameter	Description
Synchronization Type	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 selected objects from the source instance to the destination instance. The historical data is the basis for subsequent incremental synchronization. Note If Full Data Synchronization is selected, you can synchronize the schema and data of the tables that are created by using the CREATE TABLE statement to the destination database.
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 You can use the object name mapping feature to rename the tables that are synchronized to the destination database. You can use this feature if the source and destination databases contain identical table names and the tables in the destination database cannot be deleted or renamed. 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 schemas, and a data record has the same primary key value as an existing data record in the destination 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, only some columns are synchronized, or the data synchronization task fails. Operate with caution.
Data Format in Kafka	The format in which data is stored in the ApsaraMQ for Kafka instance. If you select DTS Avro, data is parsed based on the schema definition of DTS Avro. For more information, visit GitHub. If you select Canal Json, data is stored in the Canal JSON format. For more information about the related parameters and examples, see the "Canal Json" section of the Data formats of a Kafka cluster topic. Note PolarDB-X 1.0 does not support Canal Json. By default, DTS Avro is selected.
Policy for Shipping Data to Kafka Partitions	This feature is not supported.
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. Note You can select tables as the objects to be synchronized. If you select an entire database as the object to be synchronized, DTS does not synchronize the changes made to create tables in or delete tables from the source database to the destination database.
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 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 specify WHERE conditions to filter data, right-click an object in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Set filter conditions.

Click Next: Advanced Settings to configure advanced settings.

Parameter	Description
Migrate a DTS instance from a dedicated cluster to a shared cluster	In this example, you do not need to select a DTS dedicated cluster that is used to schedule the task. 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: No: does not configure alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert contacts. For more information, see Configure monitoring and alerting for a new DTS task.
Specify the retry time range 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 the 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 set different retry time ranges for multiple DTS tasks that have the same source or destination database, the shortest retry time range that is set 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.
The wait time before a retry when other issues occur in the source and destination databases	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 the 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 The wait time before a retry when other issues occur in the source and destination databases parameter must be smaller than the value of the Retry Time for Failed Connection parameter.
Configure ETL	Specifies whether to configure the extract, transform, and load (ETL) feature. For more information about ETL, see What is ETL? 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 synchronization task. No: does not configure the ETL feature.

Click Next: Save Task Settings and Precheck in the lower part of the page.
You can move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters to view the parameter settings of the API operation that is called to configure the instance.
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 task fails to pass the precheck, click View Details next to each failed item. After you troubleshoot the issues based on the causes, run a precheck again.
- 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 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.
Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.

On the Purchase Instance 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 the instance when you create an 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 charged 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 instance, you can release the pay-as-you-go instance to reduce costs.
	Resource Group	The resource group on which the instance is run. Default value: default resource group. For more information, see What is Resource Management?.
	Instance Class	DTS provides various synchronization specifications that provide different performance. The synchronization speed varies based on the synchronization specifications that you select. You can select a synchronization specification based on your business scenario. For more information, see Specifications of data synchronization instances.
	Subscription Duration	If you select the subscription billing method, set the subscription duration and the number of 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.

Read and select the check box to agree to the Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.