This topic describes how to synchronize data from an ApsaraDB RDS for MySQL instance to a Message Queue for Apache Kafka instance by using Data Transmission Service (DTS).

Prerequisites

  • The source ApsaraDB RDS for MySQL instance and the destination Message Queue for Apache Kafka instance are created.
    Note
  • In the destination Message Queue for Apache Kafka instance, a topic is created to receive the synchronized data. For more information, see Step 1: Create a topic.
  • The available storage space of the destination Message Queue for Apache Kafka instance is larger than the total size of the data in the source ApsaraDB RDS for MySQL instance.

Precautions

Category Description
Limits on the source database
  • The tables to synchronize must have PRIMARY KEY or UNIQUE constraints, and all fields must be unique. Otherwise, the destination database may contain duplicate data records.
  • If you select tables as the objects to synchronize and you want to edit tables (such as renaming tables or columns) in the destination database, up to 1,000 tables can be synchronized 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, or configure a task to synchronize the entire database.
  • The following requirements for binary logs must be met:
    • The binary logging feature is enabled. For more information about how to enable binary logging, see Modify the parameters of an ApsaraDB RDS for MySQL instance. In addition, the binlog_row_image parameter must be set to full. Otherwise, error messages are returned during precheck and the data synchronization task cannot be started.
      Notice
      • If the source database is a self-managed MySQL database, you must enable binary logging and set binlog_format to row and binlog_row_image to full.
      • If the self-managed MySQL database is deployed in a dual-primary cluster, you must set log_slave_updates to ON. This ensures that DTS can obtain all binary logs. For more information, see Create an account for a user-created MySQL database and configure binary logging.
    • For an incremental data synchronization task, the binary logs of the source database are retained for at least 24 hours. For a full data and incremental data synchronization task, the binary logs of the source database are retained for at least seven days. After full data synchronization is complete, you can set the retention period to more than 24 hours. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. Make sure that you set the retention period of binary logs in accordance with the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not ensure service reliability and performance. For more information about binary log files and log backup files of an ApsaraDB RDS for MySQL instance, see Introduction to binary log files and log backup files of an ApsaraDB RDS for MySQL instance.

Precautions
  • 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.
  • During full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data synchronization is complete, the size of the used tablespace of the destination database is larger than that of the source database.
  • If you select one or more tables instead of an entire database as the objects to synchronize, do not use gh-ost or pt-online-schema-change to perform DDL operations on the tables during data synchronization. Otherwise, data may fail to be synchronized.

    If you use only DTS to write data to the destination database, you can use Data Management (DMS) to perform online DDL operations on source tables during data synchronization. For more information, see Change schemas without locking tables.

  • 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.
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 synchronization latency is too 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 synchronize, you can create a heartbeat table. The heartbeat table is updated or receives data every second.

Size limit of a single record

The size of a single record written to Kafka is 10 MB. Therefore, if a row of source data exceeds 10 MB, the task will be interrupted because DTS cannot write data to Kafka. In this scenario, we recommend that you do not synchronize the tables that contain large fields. You can synchronize only some columns. When you configure the DTS task, you must exclude the records of these large fields. If tables that contain large fields are included in the objetcs of the task, you must remove the tables, add the tables to the objects again, and then set filter conditions to exclude the large field columns.

Supported synchronization topologies

  • One-way one-to-one synchronization
  • One-way one-to-many synchronization
  • One-way many-to-one synchronization
For more information, see Synchronization topologies.

SQL operations that can be synchronized

Operation type SQL statements
DML INSERT, UPDATE, and DELETE
DDL
  • CREATE TABLE, ALTER TABLE, DROP TABLE, RENAME TABLE, and TRUNCATE TABLE
  • CREATE VIEW, ALTER VIEW, and DROP VIEW
  • CREATE PROCEDURE, ALTER PROCEDURE, and DROP PROCEDURE
  • CREATE FUNCTION, DROP FUNCTION, CREATE TRIGGER, and DROP TRIGGER
  • CREATE INDEX and DROP INDEX

Procedure

Note This procedure is described based on the new version of the DTS console. In the event of discrepancies in operations between the console and the DTS section in the Data Management Service (DMS) console, the DMS console takes precedence.
  1. Go to the Data Synchronization page of the new DTS console.
    Note You can also log on to the Data Management console. In the top navigation bar, click DTS. Then, in the left-side navigation pane, choose DTS (DTS) > Data Synchronization.
  2. In the upper-left corner of the page, select the region where the data synchronization instance resides.
    Region
  3. Click Create Task. On the page that appears, configure the source and destination databases.
    Warning After you select the source and destination instances, we recommend that you read the Limits displayed in the upper part of the page. This ensures that you create and run the data synchronization task.
    Section Parameter Description
    N/A Task Name

    The task name that DTS automatically generates. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to use a unique task name.

    Source Database Select Instance
    Specifies whether to use an existing instance based on your needs.
    • If you use an existing instance, DTS automatically applies the parameter settings of the instance.
    • If you do not use an existing instance, you must configure the following parameters.
    Database Type Select MySQL.
    Access Method Select Alibaba Cloud Instance.
    Instance Region Select the region in which the source ApsaraDB RDS for MySQL instance resides.
    Replicate Data Across Alibaba Cloud Accounts In this example, select No because data is replicated within the same Alibaba Cloud account.
    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. The account must have the read permissions on the objects to be synchronized.
    Database Password

    The password of the database account.

    Encryption

    Select Non-encrypted or SSL-encrypted based on your requirements. If you want to select SSL-encrypted, you must enable SSL encryption for the source instance before you configure the data migration task. For more information, see Configure SSL encryption for an ApsaraDB RDS for MySQL instance.

    Destination Database Select Instance
    Specifies whether to use an existing instance based on your needs.
    • If you use an existing instance, DTS automatically applies the parameter settings of the instance.
    • If you do not use an existing instance, you must configure the following parameters.
    Database Type Select Kafka.
    Access Method Select Express Connect, VPN Gateway, or Smart Access Gateway.
    Note You cannot select Message Queue for Apache Kafka as the instance type. You can use Message Queue for Apache Kafka as a self-managed Kafka database to configure data synchronization.
    Instance Region Select the region in which the Message Queue for Apache Kafka instance resides.
    Connected VPC Select the ID of the virtual private cloud (VPC) to which the destination Message Queue for Apache Kafka instance belongs. To obtain the VPC ID, you can log on to the Message Queue for Apache Kafka console and go to the Instance Details page of the Message Queue for Apache Kafka instance. In the Basic Information section, you can view the VPC ID.
    Hostname or IP address Enter an IP address that is included in the Default Endpoint parameter of the Message Queue for Apache Kafka instance.
    Note To obtain an IP address, you can log on to the Message Queue for Apache Kafka console and go to the Instance Details page of the Message Queue for Apache Kafka instance. In the Basic Information section, you can obtain an IP address from the Default Endpoint parameter.
    Port Number Enter the service port number of the Message Queue for Apache Kafka instance. The default port number is 9092.
    Database Account Enter the database account of the Message Queue for Apache Kafka instance.
    Note If the instance type of the Message Queue for Apache Kafka instance is VPC Instance, you do not need to specify the database account or database password.
    Database Password

    Enter the password of the database account.

    Kafka Version Select the version of the Message Queue for Apache Kafka instance.
    Encryption Select Non-encrypted or SCRAM-SHA-256 based on your business and security requirements.
    Topic Select a topic from the drop-down list.
    Topic That Stores DDL Information Select a topic from the drop-down list. The topic is used to store the DDL information. 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 Kafka Schema Registry provides a serving layer for your metadata. It provides a RESTful API for storing and retrieving your Avro schemas.
    • No: Kafka Schema Registry is not used.
    • Yes: Kafka Schema Registry is used. In this case, you must enter the URL or IP address that is registered in Kafka Schema Registry for your Avro schemas.
  4. If a whitelist is configured for your self-managed database, you must add the CIDR blocks of DTS servers to the whitelist. Then, click Test Connectivity and Proceed.
    Note For more information about the CIDR blocks of DTS servers, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.
  5. Select the objects to migrate.
    • Basic Settings
      Parameter Description
      Task Stages

      Incremental Data Synchronization is selected by default. 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 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 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 migrated 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 schema, and a data record has the same primary key 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, initial data synchronization may fail. In this case, only part of the columns are synchronized, or the data synchronization task fails.
      Data Format in Kafka Select the format in which data records are stored in the Message Queue for Apache Kafka instance.
      • If you select DTS Avro, data is parsed based on the schema definition of DTS Avro. For more information about the schema definition, 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 in Data formats of a Kafka cluster.
      Policy for Shipping Data to Kafka Partitions Select a synchronization policy based on your business requirements. For more information, see Specify the policy for migrating data to Kafka partitions.
      Select Objects

      Select one or more objects from the Source Objects section and click the Rightwards arrow icon to add the objects to the Selected Objects section.

      Note You can select only tables as the objects to be synchronized.
      Rename Databases and Tables
      • To rename an object in 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 in the destination instance, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time.
      Filter data

      You can specify WHERE conditions to filter data. For more information, see Use SQL conditions to filter data.

      Select the SQL operations to be synchronized In the Selected Objects section, right-click an object. In the dialog box that appears, select the DML and DDL operations that you want to synchronize. For more information, see SQL operations that can be synchronized.
    • Advanced Settings
      Parameter Description
      Set Alerts
      Specifies whether to set alerts for the data synchronization task. If you select yes, DTS sends notifications to contacts if the task fails or the synchronization latency exceeds the upper limit.
      • No: does not set alerts.
      • Yes: sets alerts. In this case, you must also set the alert threshold and alert contacts.
      Capitalization of Object Names in Destination Instance

      Specifies the capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to make sure that the capitalization of object names is consistent with that of the source or destination database. For more information,see Specify the capitalization of object names in the destination instance.

      Retry Time for Failed Connection
      Specifies the retry time range for failed connections. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the retry time range to more than 30 minutes. 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 an instance serves as the source or destination database of multiple data synchronization tasks, the less value that is specified for the instance 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 needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
  6. 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 task fails to pass the precheck, you can click the Info icon icon next to each failed item to view details.
      • After you troubleshoot the issues based on the causes, you can run a precheck again.
      • If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.
  7. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.
  8. On the Purchase Instance page, specify the billing method and specifications for the data synchronization instance. The following table describes related parameters.
    Section Parameter Description
    Parameters Billing method
    • Subscription: You pay for your subscription 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 billed on an hourly basis. For short-term use, we recommend that you select the pay-as-you-go billing method. If you no longer need a pay-as-you-go instance, you can release the instance to reduce costs.
    Instance Class DTS provides several instance classes that have different performance in synchronization speed. You can select an instance class 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 or one to three years.
    Note This parameter is available only if you select the subscription billing method.
  9. Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
  10. Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.