Updated on 2022-08-16 GMT+08:00

From MySQL to MySQL

Supported Source and Destination Databases

Table 1 Supported Databases

Source DB

Destination DB

  • RDS for MySQL
  • On-premises MySQL databases
  • MySQL databases on an ECS
  • MySQL databases on other clouds
  • RDS for MySQL

Prerequisites

  • You have logged in to the DRS console.
  • For details about the DB types and versions supported by real-time migration, see Real-Time Migration.

Suggestions

  • When a task is being started or in the full migration phase, do not perform DDL operations on the source database. Otherwise, the task may be abnormal.
  • To maintain data consistency before and after the migration, do not write data to the source and destination databases in the full migration mode. In the full+incremental migration mode, you can continue the migration while data is still being written to the source database.
  • The success of migration depends on environment and manual operations. You can run a migration test before you start the full-scale migration to help you detect and resolve problems in advance.
  • Start your migration task during off-peak hours. A less active database is easier to migrate successfully. If the data is fairly static, there is less likely to be any severe performance impacts during the migration.
    • If network bandwidth is not limited, the query rate of the source database increases by about 50 MB/s during full migration, and two to four CPUs are occupied.
    • To ensure data consistency, tables to be migrated without a primary key may be locked for 3s.
    • The data being migrated may be locked by other transactions for a long period of time, resulting in read timeout.
    • Due to the inherent characteristics of MySQL, in some scenarios the performance may be negatively affected. For example, if the CPU resources are insufficient and the storage engine is TokuDB, the read speed on tables may be decreased by 10%.
    • If DRS concurrently reads data from a database, it will use about 6 to 10 sessions. The impact of the connections on services must be considered.
    • If you read a table, especially a large table, during the full migration, the exclusive lock on that table may be blocked.
  • Data-level comparison

    To obtain accurate comparison results, compare data at a specified time point during off-peak hours. If it is needed, select Start at a specified time for Comparison Time. Due to slight time difference and continuous operations on data, inconsistent comparison results may be generated, reducing the reliability and validity of the results.

Precautions

Before creating a migration task, read the following notes:

Table 2 Precautions

Type

Restrictions

Precautions

  • Data cannot be migrated from a newer version database to an older version database.
  • Objects that have dependencies must be migrated at the same time to avoid migration failure. Common dependencies: tables referenced by views, views and tables referenced by stored procedures/functions/triggers, and tables referenced by primary and foreign keys
  • Cascade operations cannot be performed on tables with foreign keys.
  • The primary/standby switchover is not supported if GTID is not enabled for the source database.
  • If the source and destination sides are RDS MySQL instances, transparent data encryption (TDE) is not supported, and tables with the encryption function cannot be created.
  • If the destination MySQL database does not support TLS 1.2 or is a self-built database of an earlier version (earlier than 5.6.46 or between 5.7 and 5.7.28), you need to submit an O&M application for testing the SSL connection.
  • Resumable upload is supported, but data may be repeatedly inserted into a table that does not have a primary key.
  • During migration, do not modify or delete the usernames, passwords, permissions, or ports of the source and destination databases.
  • During the migration, you are not advised to perform a primary/standby switchover on the destination database.
  • Ensure that the destination database is publicly accessible before the migration task is complete.
  • During migration, do not write the statement-based binlog into the source database.
  • During migration, do not clear the binlog in the source database.
  • During full migration, DDL operations such as table structure modification are not supported.
  • The destination DB instance must be readable and writable. Otherwise, the migration may fail.

Procedure

This section uses the migration from an RDS MySQL database to a MySQL database on an ECS as an example to describe how to configure a migration task in a VPC network on the DRS management console.

  1. On the Online Migration Management page, click Create Migration Task.
  2. On the Create Replication Instance page, configure task details, description, and the replication instance, and click Next.

    Table 3 Task information

    Parameter

    Description

    Task Name

    The task name consists of 4 to 50 characters, starts with a letter, and can contain only letters (case-insensitive), digits, hyphens (-), and underscores (_).

    Description

    The description consists of a maximum of 256 characters and cannot contain special characters !=<>'&"\

    Table 4 Replication instance settings

    Parameter

    Description

    Data Flow

    Select Out of the cloud.

    The source database is a database on the current cloud.

    Source DB Engine

    Select MySQL.

    Destination DB Engine

    Select MySQL.

    Network Type

    Available options: Public network, VPC, VPN or Direct Connect

    • VPC is suitable for migrations of cloud databases.
    • VPN and Direct Connect are suitable for migrations from on-premises databases to cloud databases or between cloud databases across regions.
    • Public network is suitable for migrations from on-premises databases or external cloud databases to destination databases.

    Source DB Instance

    Select the DB instance whose data is to be migrated out of the cloud.

    Replication Instance Subnet

    The subnet where the replication instance resides. You can also click View Subnet to go to the network console to view the subnet where the instance resides.

    By default, the DRS instance and the destination DB instance are in the same subnet. You need to select the subnet where the DRS instance resides, and there are available IP addresses for the subnet. To ensure that the replication instance is successfully created, only subnets with DHCP enabled are displayed.

    Migration Type

    • Full: This migration type is suitable for scenarios where service interruption is acceptable. All objects and data in non-system databases are migrated to the destination database at one time. The objects include tables, views, and stored procedures.
      NOTE:

      If you are performing a full migration, do not perform operations on the source database. Otherwise, data generated in the source database during the migration will not be synchronized to the destination database.

    • Full+Incremental: This migration type allows you to migrate data without interrupting services. After a full migration initializes the destination database, an incremental migration initiates and parses logs to ensure data consistency between the source and destination databases.
    NOTE:

    If you select Full+Incremental, data generated during the full migration will be continuously synchronized to the destination database, and the source remains accessible.

  3. On the Configure Source and Destination Databases page, wait until the replication instance is created. Then, specify source and destination database information and click Test Connection for both the source and destination databases to check whether they have been connected to the replication instance. After the connection tests are successful, select the check box before the agreement and click Next.

    Table 5 Source database settings

    Parameter

    Description

    DB Instance Name

    The RDS DB instance selected during migration task creation. This parameter cannot be changed.

    Database Username

    Enter the username of the source database.

    Database Password

    The password for the database username.

    If the task is in the Starting, Full migration, Incremental migration, or Incremental migration failed status, in the Migration Information area on the Basic Information page, click Update Password next to the Source Database Password field. In the displayed dialog box, change the password. This action only updates DRS with the changed password.

    The username and password of the source database are encrypted and stored in the database and the replication instance during the migration. After the task is deleted, the username and password are permanently deleted.

    Table 6 Destination database settings

    Parameter

    Description

    VPC

    A dedicated virtual network in which the destination database is located. It isolates networks for different services.

    Subnet

    A subnet provides dedicated network resources that are isolated from other networks, improving network security. The subnet must be in the AZ where the source database resides. You need to enable DHCP for creating the source database subnet.

    IP Address or Domain Name

    Enter the IP address or domain name of the destination database.

    Port

    The port of the destination database. Range: 1 - 65535

    Database Username

    The username for accessing the destination database.

    Database Password

    The password for the database username. You can change the password if necessary. To change the password, perform the following operation after the task is created:

    If the task is in the Starting, Full migration, Incremental migration, or Incremental migration failed status, in the Migration Information area on the Basic Information page, click Update Password next to the Destination Database Password field. In the displayed dialog box, change the password. This action only updates DRS with the changed password.

    SSL Connection

    SSL encrypts the connections between the source and destination databases. If SSL is enabled, upload the SSL CA root certificate.

    NOTE:
    • The maximum size of a single certificate file that can be uploaded is 500 KB.
    • If the SSL certificate is not used, your data may be at risk.

    Migrate Definer to User

    • Yes
    • No

      The Definers of all source database objects will not be changed. You need to migrate all accounts and permissions of the source database in the next step.

    The IP address, port, username, and password of the destination database are encrypted and stored in the database and the replication instance, and will be cleared after the task is deleted.

  4. On the Set Task page, set migration accounts and objects, and click Next.

    Table 7 Migration types and objects

    Parameter

    Description

    Flow Control

    You can choose whether to control the flow.

    • Yes

      You can customize the maximum migration speed.

      In addition, you can set the time range based on your service requirements. The traffic rate setting usually includes setting of a rate limiting time period and a traffic rate value. Flow can be controlled all day or during specific time ranges. The default value is All day. A maximum of three time ranges can be set, and they cannot overlap.

      The flow rate must be set based on the service scenario and cannot exceed 9,999 MB/s.

    • No
      The migration speed is not limited and the outbound bandwidth of the source database is maximally used, which will increase the read burden on the source database. For example, if the outbound bandwidth of the source database is 100 MB/s and 80% bandwidth is used, the I/O consumption on the source database is 80 MB/s.
      NOTE:
      • Flow control mode takes effect only during a full migration.
      • You can also change the flow control mode after creating a task. For details, see Modifying the Flow Control Mode.

    Filter DROP DATABASE

    During an incremental migration, executing DDL operations on the source database may affect the data migration performance to some extent. To reduce data migration risks, DRS allows you to filter out DDL operations.

    The database deletion operation can be filtered by default.

    • If you select Yes, any database deletion operations performed on the source database are not synchronized during data migration.
    • If you select No, related operations are synchronized to the destination database during data migration.
      NOTE:

      Currently, only the full plus incremental migrations from RDS MySQL to MySQL are supported.

    Migrate Account

    During a database migration, accounts need to be migrated separately.

    There are accounts that can be migrated completely, accounts whose permissions need to be reduced, and accounts that cannot be migrated. You can choose whether to migrate the accounts based on service requirements.
    • No

      During the migration, accounts, permissions, and passwords are not migrated.

    Migrate Object

    You can choose to migrate all objects, tables, or databases based on your service requirements.

    • All: All objects in the source database are migrated to the destination database. After the migration, the object names will remain the same as those in the source database and cannot be modified.
    • Tables: The selected table-level objects will be migrated.
    • Databases: The selected database-level objects will be migrated.

    If the source database is changed, click in the upper right corner before selecting migration objects to ensure that the objects to be selected are from the changed source database.

    NOTE:
    • If you choose not to migrate all of the databases, the migration may fail because the objects, such as stored procedures and views, in the databases to be migrated may have dependencies on other objects that are not migrated. To prevent migration failure, migrate all of the databases.
    • When you select an object, the spaces before and after the object name are not displayed. If there are two or more consecutive spaces in the middle of the object name, only one space is displayed.
    • The search function can help you quickly select the required database objects.

  5. On the Check Task page, check the migration task.

    • If any check fails, review the cause and rectify the fault. After the fault is rectified, click Check Again.
    • If the check is complete and the check success rate is 100%, click Next.

      You can proceed to the next step only when all checks are successful. If there are any items that require confirmation, view and confirm the details first before proceeding to the next step.

  6. On the displayed page, specify Start Time and confirm that the configured information is correct and click Submit to submit the task.

    Table 8 Task startup settings

    Parameter

    Description

    Started Time

    Set Start Time to Start upon task creation or Start at a specified time based on site requirements. The Start at a specified time option is recommended.

    NOTE:

    The migration task may affect the performance of the source and destination databases. You are advised to start the task in off-peak hours and reserve two to three days for data verification.

  7. After the task is submitted, view and manage it on the Online Migration Management page.

    • You can view the task status. For more information about task status, see Task Statuses.
    • You can click in the upper right corner to view the latest task status.