tencent cloud

Overview

This document describes how to use the data migration feature of DTS to migrate data from a self-built database to a TencentDB database through CCN.

CCN can interconnect a VPC with another VPC or a local IDC. To use CCN access, you must establish cross-VPC and VPC-IDC interconnections through CCN in advance.

In this scenario, you have used CCN to interconnect the three networks of VPC-Guangzhou, VPC-Chengdu, and VPC-Shanghai, have a self-built database in Guangzhou, and plan to migrate the data in the source database in Guangzhou to the target database in Nanjing. VPC-Chengdu is selected as the Accessed VPC.

Configuration Principles

When selecting CCN access, you need to connect the source database to the source of the DTS migration/sync linkage over CCN as follows: source database > accessed VPC > source of the migration/sync linkage, as shown in orange below.

The accessed VPC and the source of the migration/sync linkage are interconnected as follows in the entire DTS task:

• The source of the migration/sync linkage is the network in the region of the source database selected during the task purchase, as shown below:
  The region of the source database selected during task purchase must be the same as the region of the accessed VPC; otherwise, the networks cannot be interconnected, and DTS will change the former to the latter.

  

• Accessed VPC: The accessed VPC refers to the VPC in CCN over which the migration/sync linkage is connected. It can be configured when you set the source and target databases as shown below:
  The accessed VPC and the VPC of the source database are interconnected over CCN.

Notes

• When DTS performs full data migration, it will occupy certain source instance resources, which may increase the load of the source instance and the database pressure. If your database has low configurations, we recommend that you migrate data during off-peak hours.
• Migration is implemented without locks by default, during which no global lock (the FTWRL lock) is added to the source database, and only tables without a primary key are locked.

Prerequisites

• You have created a TencentDB for MySQL instance as instructed in Creating MySQL Instance.

• The source and target databases must meet the requirements for the migration feature and version as instructed in Databases Supported by Data Migration.

• You have completed all preparations as instructed in Overview.

• The source database must have the following permissions:

  • Migration of the entire instance:

    CREATE USER 'migration account'@'%' IDENTIFIED BY 'migration password';  
    GRANT RELOAD,LOCK TABLES,REPLICATION CLIENT,REPLICATION SLAVE,SHOW DATABASES,SHOW VIEW,PROCESS ON *.* TO 'migration account'@'%';  
    GRANT ALL PRIVILEGES ON `__tencentdb__`.* TO 'migration account'@'%';  
    GRANT SELECT ON *.* TO 'migration account';
    

  • Migration of specified objects:

    CREATE USER 'migration account'@'%' IDENTIFIED BY 'migration password';  
    GRANT RELOAD,LOCK TABLES,REPLICATION CLIENT,REPLICATION SLAVE,SHOW DATABASES,SHOW VIEW,PROCESS ON *.* TO 'migration account'@'%';  
    GRANT ALL PRIVILEGES ON `__tencentdb__`.* TO 'migration account'@'%';  
    GRANT SELECT ON `mysql`.* TO 'migration account'@'%';
    GRANT SELECT ON database to be migrated.* TO 'migration account';
    

• Permissions required of the target database: ALTER, ALTER ROUTINE, CREATE, CREATE ROUTINE, CREATE TEMPORARY TABLES, CREATE USER, CREATE VIEW, DELETE, DROP, EVENT, EXECUTE, INDEX, INSERT, LOCK TABLES, PROCESS, REFERENCES, RELOAD, SELECT, SHOW DATABASES, SHOW VIEW, TRIGGER, and UPDATE.

Application Restrictions

• Basic tables, views, functions, triggers, stored procedures, and events can be migrated, while system tables such as information_schema, sys, performance_schema, __cdb_recycle_bin__, __recycle_bin__, __tencentdb__, and mysql cannot.
• When views, stored procedures, and functions are migrated, DTS will check whether user1 corresponding to DEFINER ([DEFINER = user1]) in the source database is the same as the migration account user2, and if not, DTS will change the SQL SECURITY attribute of user1 in the target database from DEFINER to INVOKER ([INVOKER = user1]) after the migration, and set the DEFINER in the target database to the migration account user2 ([DEFINER = migration account user2]). If the view definition in the source database is too complex, the task may fail.
• If the source MySQL database is a non-GTID database, DTS doesn't support HA switch for it. If it is switched, DTS incremental sync may be interrupted.
• Only data with the following three database engines can be migrated: InnoDB, MyISAM, and TokuDB. Tables with other engines will be skipped during migration by default.
• Correlated data objects must be migrated together; otherwise, migration will fail. Common correlations include table reference by views, view reference by views, and tables correlated through primary/foreign keys.
• During incremental migration, if the source database has distributed transactions or generates binlog statements in the STATEMENT format, the migration will fail.
• In migration without locks (the source database is Alibaba Cloud ApsaraDB RDS for MySQL 5.6, Alibaba Cloud PolarDB for MySQL 5.6, or Amazon RDS for MySQL, and the target database is TencentDB for MySQL), DDL operations are not supported during full migration.

Operation Limits

• During migration, do not perform the following operations; otherwise, the migration task will fail:
  • Do not modify or delete user information (including username, password, and permissions) in the source and target databases and port numbers.
  • Do not run distributed transactions in the source database.
  • Do not write binlog data in the STATEMENT format into the source database.
  • Do not clear binlogs in the source database.
  • Do not run DDL operations of changing the database/table structure during database/table structure migration or full migration.
  • Do not delete the system table __tencentdb__ during incremental migration.
• If you only perform full data migration, do not write new data into the source instance during migration; otherwise, the data in the source and target databases will be inconsistent. In scenarios with data writes, to ensure the data consistency in real time, we recommend you select full + incremental data migration.

Supported SQL Operations

Environment Requirements

Note：

The system will automatically check the following environment requirements before starting a migration task and report an error if a requirement is not met. If you can identify the failed check item, fix it as instructed in Database Connection Check; otherwise, wait for the system verification to complete and fix the problem according to the error message.

Directions

Configuring the network interconnection through CCN

Establish interconnections as instructed in Connecting Network Instances Under the Same Account.

Note：

CCN only provides bandwidth below 10 Kbps between all regions free of charge. However, DTS requires a higher bandwidth. Therefore, bandwidth configuration in the link is required.

Configuring a DTS migration task

1. Log in to the DTS console, select Data Migration on the left sidebar, and click Create Migration Task to enter the Create Migration Task page.

2. On the Create Migration Task page, select the types, regions, and specifications of the source and target instances and click Buy Now.

3. On the Set source and target databases page, configure the task, source database, and target database settings. After the source and target databases pass the connectivity test, click Create.

   Note：

   If the connectivity test fails, troubleshoot and fix the problem as prompted and as instructed in Database Connection Check and try again.

   Setting Type	Configuration Item	Description
   Task Configuration	Task Name	Set a meaningful name for easy task identification.
   	Running Mode	Immediate execution: The task will be started immediately after the task verification is passed. Scheduled execution: You need to configure a task execution time and the task will be started automatically then.
   	Tag	Tags are used to manage resources by category in different dimensions. If the existing tags do not meet your requirements, go to the console to create more.
   Source Database Settings	Source Database Type	The source database type selected during purchase, which cannot be changed.
   	Service Provider	Select Others.
   	Region	The source database region selected during purchase, which cannot be changed.
   	Access Type	Select CCN. For more information on access types, see Overview.
   	Host Address	IP address or domain name for accessing the source MySQL database.
   	Port	Port for accessing the source MySQL database.
   	Account	Account of the source MySQL database, which must have the required permissions.
   	Password	Password of the source MySQL database.
   	VPC-based CCN Instance	Only VPC-based CCN instance is supported. You need to confirm the network type associated with CCN.
   	Accessed VPC	The accessed VPC refers to the VPC in CCN over which the migration/sync linkage is connected. You need to select a CCN-associated VPC other than the VPC where the source database resides. To ensure the network connectivity, you must check whether the following key requirements are met: The selected CCN-associated VPC cannot be in the same region as the host address of the source database. If the source database is MySQL in a self-built IDC, this restriction can be ignored. The selected CCN-associated VPC cannot be in the same VPC as the host address of the source database. If the source database is MySQL in a self-built IDC, the selected VPC cannot be the VPC of the Direct Connect gateway associated with the self-built IDC.
   	Subnet	Name of the subnet of the selected VPC. If you cannot pull the subnet, there may be a problem with your account. The account of the accessed VPC must be the same as the migration account. For example, to migrate a database under account A to account B, you should use account B to create a task. Therefore, the accessed VPC must be under account B.
   	Region of Accessed VPC	The region of the source database selected during task purchase must be the same as the region of the accessed VPC; otherwise, DTS will change the former to the latter.
   Target Database Settings	Target Database Type	The target database type selected during purchase, which cannot be changed.
   	Region	The target database region selected during purchase, which cannot be changed.
   	Access Type	Select Database.
   	Database Instance	Select the instance ID of the target TencentDB database.
   	Account	The account of the target TencentDB database, which needs to have required permissions.
   	Password	Password of the target TencentDB database.

4. On the Set migration options and select migration objects page, configure the migration type and objects and click Save.

   Configuration Item	Description
   Migration Type	Select a type based on your scenario. Structural migration: Structured data such as databases and tables in the database will be migrated. Full migration: The entire database will be migrated. Full + incremental migration: The entire database and subsequent incremental data will be migrated. If there are data writes during migration, and you want to smoothly migrate the data in a non-stop manner, select this option.
   Migration Object	Entire instance: Migrate the entire database instance excluding the system databases such as `information_schema`, `mysql`, `performance_schema`, and `sys`. Specified objects: Migrate specified objects.
   Specified objects	Select the objects to be migrated in Source Database Object and move them to the Selected Object box.

5. On the task verification page, verify the task. After the verification is passed, click Start Task.
   If the verification failed, fix the problem as instructed in Database Connection Check and initiate the verification task again.

• Failed: It indicates that a check item fails and the task is blocked. You need to fix the problem and run the verification task again.
• Alarm: It indicates that a check item doesn't completely meet the requirements, and the task can be continued, but the business will be affected. You need to assess whether to ignore the alarm or fix the problem and continue the task based on the alarm message.

6. Return to the data migration task list, and you can see that the task has entered the Creating status. After 1–2 minutes, the data migration task will be started.

• Select Structural migration or Full migration: once completed, the task will be stopped automatically.
• Select Full + Incremental migration: After full migration is completed, the migration task will automatically enter the incremental data sync stage, which will not stop automatically. You need to click Complete to manually stop the incremental data sync.
  • Manually complete incremental data sync and business switchover at appropriate time.
  • Observe whether the migration task is in the incremental sync stage and is not in the lag status. If so, stop writing data to the source database for a few minutes.
  • Manually complete incremental sync when the data gap between the target and the source databases is 0 MB and the time lag between them is 0 seconds.

7. (Optional) If you want to view, delete, or perform other operations on a task, click the task and select the target operation in the Operation column. For more information, see Viewing Task.

Business cutover

After the migration task status becomes Task successful, you can formally cut over the business. For more information, see Cutover Description.