This topic describes how to migrate data from an ApsaraDB RDS for MySQL instance to a DataHub project by using Data Transmission Service (DTS).

Prerequisites

Precautions

Category Description
Limits on the source database
  • Bandwidth requirements: The server to which the source database belongs must have sufficient egress bandwidth. Otherwise, the data migration speed is affected.
  • The tables to be migrated 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 be migrated and you need to edit tables (such as renaming tables or columns), up to 1,000 tables can be migrated in a single data migration task. If you run a task to migrate more than 1,000 tables, a request error occurs. In this case, we recommend that you split the tables to be migrated, configure multiple tasks to migrate the tables, or configure a task to migrate the entire database.
  • If you need to migrate incremental data, you must make sure that the following requirements are met:
    • The binary logging feature must be enabled. The value of the binlog_format parameter must be set to row. The value of the binlog_row_image parameter must be set to full. Otherwise, error messages are returned during precheck and the data migration task cannot be started.
      Notice If the self-managed MySQL database is deployed in a dual-primary cluster), you must set the log_slave_updates parameter to ON. This setting ensures that DTS can obtain all binary logs.

    • If you perform only incremental data migration, the binary logs of the source database must be stored for more than 24 hours. If you perform both schema migration and incremental data migration, the binary logs of the source database must be stored for at least seven days. After schema migration is completed, 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 extreme cases, data may be inconsistent or lost. Make sure that you set the retention period of binary logs based on the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not guarantee service reliability and performance.

  • Limits on operations: During schema migration, do not perform DDL operations to change the schemas of databases or tables. Otherwise, the data migration task fails.
Other limits
  • Only tables can be selected as the objects to be migrated.
  • We recommend that you do not use gh-ost or pt-online-schema-change to perform DDL operations on objects during data migration. Otherwise, data migration may fail.
  • 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 migration. For more information, see Change schemas without locking tables.
    Warning If you use tools other than DTS to write data to the destination database, we recommend that you do not use DMS to perform online DDL operations. Otherwise, data loss may occur in the destination database.
  • You must make sure that the precision settings for columns of the FLOAT or DOUBLE data type meets your business requirements. DTS uses the ROUND(COLUMN,PRECISION) function to retrieve values from columns of the FLOAT or DOUBLE data type. If you do not specify a precision, DTS sets the precision for the FLOAT data type to 38 digits and the precision for the DOUBLE data type to 308 digits.
  • DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch workloads to the destination instance, stop or release the data migration task. You can also run the revoke command to revoke the write permissions from the accounts that are used by DTS to access the destination instance. Otherwise, the data in the source database will overwrite the data in the destination instance after the task is resumed.
Special cases
If the source database is a self-managed MySQL database, take note of the following limits:
  • If you perform a primary/secondary switchover on the source database when the data migration task is running, the task fails.
  • DTS calculates migration latency based on the timestamp of the latest migrated data in the destination database and the current timestamp in the source database. If no data manipulation language (DML) operation is performed on the source database for a long time, the migration latency may be inaccurate. If the latency of the migration task 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 be migrated, you can create a heartbeat table. The heartbeat table is updated or receives data every second.

Billing

Migration type Task configuration fee Internet traffic fee
Schema migration Free of charge. Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Pricing.

Migration types

SQL operations that can be migrated

Operation type SQL statement
DML INSERT, UPDATE, and DELETE
Notice To migrate a new column in the source table by using DTS, you must first add a column in the destination table. Then, add the new column in the source table.DataHub

Permissions required for database accounts

Database Required permissions
Source ApsaraDB RDS for MySQL instance The read permissions on the objects to migrate

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. 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 at the top of the page. This helps you create and run the data synchronization task.
    Section Parameter Description
    None Task Name

    DTS automatically generates a task name. We recommend that you specify an informative name to identify the task. You do not need to use a unique task name.

    Source Database
    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. For information about the permissions that are required for the account, see Permissions required for database accounts.
    Database Password

    Enter the password of the database account.

    Encryption

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

    Destination Database
    Database Type Select DataHub.
    Access Method Select Alibaba Cloud Instance.
    Instance Region Select the region in which the DataHub instance resides.
    Project Select the destination DataHub instance for Project.
  2. Select objects for the task and configure advanced settings.
    • Basic Settings
      Parameter Description
      Task Stages You can select only Schema Migration and Incremental Data Migration. Full Data Migration cannot be selected.
      Note If Incremental Data Migration is not selected, we recommend that you do not write data to the source instance during data migration. This ensures data consistency between the source and destination instances.
      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 migration 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 consistency is not guaranteed 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 incremental data migration, DTS migrates 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 migration may fail. In this case, only some columns are migrated, or the data migration task fails.
      Apply New Naming Rules of Additional Columns
      After DTS synchronizes data to DataHub, DTS adds additional columns to the destination topic. If the names of additional columns are the same as the names of existing columns in the destination topic, data synchronization fails. Select Yes or No to specify whether you want to enable the new naming rules for additional columns.
      Warning Before you specify this parameter, check whether additional columns and existing columns in the destination topic have name conflicts. For more information, see Modify the naming rules for additional columns.
      Note You can select only databases as the objects to migrate.
      Rename Databases and Tables

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

      In the Selected Objects section, right-click an object. In the dialog box that appears, select the DML operations that you want to migrate. For more information, see SQL operations that can be migrated.
    • Advanced Settings
      Parameter Description
      Capitalization of Object Names in Destination Instance

      Specify 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
      Specify the retry time for failed connections. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the retry time to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified time, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails.
      Note
      • If multiple DTS instances have the same source or destination database, the lowest value takes effect. For example, the retry time is set to 30 minutes for Instance A and 60 minutes for Instance B, DTS retries failed connections at an interval of 30 minutes.
      • When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time based on your business needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
  3. 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.
      • You can troubleshoot the issues based on the causes and run a precheck again.
      • If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.
  4. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.
  5. Read and select Data Transmission Service (Pay-as-you-go) Service Terms.