From MySQL to MySQL

Supported Source and Destination Databases

Prerequisites

• You have logged in to the DRS console.
• Your account balance is greater than or equal to $0 USD.
• For details about the DB types and versions supported by real-time migration, see Supported Databases.
• If a subaccount is used to create a DRS task, ensure that an agency has been added. To create an agency, see Agency Management.

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 you have to migrate data during peak hours, you can select Yes for Flow Control to adjust the migration speed.
  • 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.
  • For more information about the impact of DRS on databases, see What Is the Impact of DRS on Source and Destination Databases?
• 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:

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, select a region, configure task details, description, and the replication instance, and click Next.
   Figure 1 Migration task information
   

   Table 3 Task information

   Parameter	Description
   Region	The region where the replication instance is deployed. You can change the region. To reduce latency and improve access speed, select the region closest to your services.
   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 can contain up to 256 characters and cannot contain special characters !=<>&'\"

   Figure 2 Replication instance information
   

   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.
   Enterprise Project	If the DB instance has been associated with an enterprise project, select the target project from the Enterprise Project drop-down list. You can also go to the ProjectMan console to create a project. For details about how to create a project, see the ProjectMan User Guide.
   Tags	This setting is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 10 tags. After a task is created, you can view its tag details on the Tags tab. For details, see Tag Management.

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.
   Figure 3 Source database information
   

   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.

   Figure 4 Destination database information
   

   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 The Definers of all source database objects will be migrated to the user. Other users do not have permissions for database objects unless these users are authorized. For details about authorization, see How Do I Maintain the Original Service User Permission System After Definer Is Forcibly Converted During MySQL Migration? 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.
   Figure 5 Migration Type
   

   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. Figure 6 Flow control 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.
   Take Snapshot	If you perform a full migration, you can take a snapshot for your databases. No This option applies to exports for which no data is written to the source database. If data is modified during a full migration, the exported data is point in time inconsistent. The stability and performance of a migration without a snapshot taken is better than that of a migration with a snapshot taken. Yes A snapshot with consistent data at the point in time is generated during service running. Data changes during migration are not shown in the exported data. NOTE: Snapshot reads use MySQL backup lock to lock global tables and automatically unlock them within 3s after consistent reads are enabled. To prevent full migration failures, take a snapshot when the source database is idle and does not perform DML or DDL operations during snapshot migration. The snapshot function is supported only for full migration of databases whose engine is MySQL.
   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. If you select Yes, you can select the accounts to be migrated as required. Yes If you need to migrate accounts, see Migrating Accounts. 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.

     For details about how to handle check failures, see Checking Whether the Source Database Is Connected in Data Replication Service User Guide.

     Figure 7 Pre-check
     
   • 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, Send Notification, SMN Topic, Synchronization Delay Threshold, and Stop Abnormal Tasks After and confirm that the configured information is correct and click Submit to submit the task.
   Figure 8 Task startup settings
   

   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.
   Send Notifications	SMN topic. This parameter is optional. If an exception occurs during migration, the system will send a notification to the specified recipients.
   SMN Topic	This parameter is available only after you enable Send Notifications and create a topic on the SMN console and add a subscriber. For details, see Simple Message Notification User Guide.
   Synchronization Delay Threshold	During an incremental migration, a synchronization delay indicates a time difference (in seconds) of synchronization between the source and destination database. If the synchronization delay exceeds the threshold you specify, DRS will send alarms to the specified recipients. The value ranges from 0 to 3,600. To avoid repeated alarms caused by the fluctuation of delay, an alarm is sent only after the delay has exceeded the threshold for six minutes. NOTE: In the early stages of an incremental migration, there is more delay because more data is waiting to be synchronized. In this situation, no notifications will be sent. Before setting the delay threshold, enable Send Notification. If the delay threshold is set to 0, no notifications will be sent to the recipient.
   Stop Abnormal Tasks After	Number of days after which an abnormal task is automatically stopped. The value must range from 14 to 100. The default value is 14. NOTE: Tasks in the abnormal state are still charged. If tasks remain in the abnormal state for a long time, they cannot be resumed. Abnormal tasks run longer than the period you set (unit: day) will automatically stop to avoid unnecessary fees.

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.