From MySQL to MySQL

Supported Source and Destination Databases

Table 1 Supported databases
Disaster Recovery Relationship	Service Database	DR Database
Current cloud as standby	On-premises MySQL databases MySQL databases on an ECS MySQL databases on other clouds RDS for MySQL	RDS for MySQL
Current cloud as active	RDS for MySQL	On-premises MySQL databases MySQL databases on an ECS MySQL databases on other clouds RDS for MySQL

Database Account Permission Requirements

To start a DR task, the service and DR database users must meet the requirements in the following table. Different types of DR tasks require different permissions. For details, see Table 2. DRS automatically checks the database account permissions in the pre-check phase and provides handling suggestions.

Table 2 Database account permission
Type	Permission Required
Service database user	The user must have the following permissions: SELECT, CREATE, ALTER, DROP, DELETE, INSERT, UPDATE, TRIGGER, REFERENCES, SHOW VIEW, EVENT, INDEX, LOCK TABLES, CREATE VIEW, CREATE ROUTINE, ALTER ROUTINE, CREATE USER, RELOAD, REPLICATION SLAVE, REPLICATION CLIENT, and WITH GRANT OPTION. The user root of the RDS for MySQL instance has the preceding permissions by default. If the service database version is 8.0.14 to 8.0.18, the SESSION_VARIABLES_ADMIN permission is required. If the service database version is 8.0.2 or later, the XA_RECOVER_ADMIN permission is required to prevent data loss caused by uncommitted XA transactions during startup. The root account of the RDS for MySQL DB instance has the preceding permissions by default.
DR database user	The user must have the following permissions: SELECT, CREATE, ALTER, DROP, DELETE, INSERT, UPDATE, TRIGGER, REFERENCES, SHOW VIEW, EVENT, INDEX, LOCK TABLES, CREATE VIEW, CREATE ROUTINE, ALTER ROUTINE, CREATE USER, RELOAD, REPLICATION SLAVE, REPLICATION CLIENT, and WITH GRANT OPTION. The user root of the RDS for MySQL instance has the preceding permissions by default. If the DR database version is 8.0.14 to 8.0.18, the SESSION_VARIABLES_ADMIN permission is required.

Note

You are advised to create an independent database account for DRS task connection to prevent task failures caused by database account password modification.
After changing the account passwords for the service and DR databases, modify the connection information of the DRS task by referring to Modifying Connection Information to prevent automatic retry after a task failure. Automatic retry will lock the database accounts.
Table 2 lists the minimum permissions required by a DRS task. If you need to migrate the grant permission through a DRS task, ensure that the connection account of the DRS task has the corresponding permission. Otherwise, the destination database user may not be authorized due to grant execution failure. For example, if the connection account of the DRS task does not require the process permission, but you need to migrate the process permission through a DRS task, ensure that the connection account of the DRS task has the process permission.

Prerequisites

You have logged in to the DRS console.
For details about the supported DB types and versions, see Real-Time Disaster Recovery.

Suggestions

Caution

During the DR initialization, do not perform DDL operations on the service database. Otherwise, the task may be abnormal.
During DR initialization, ensure that no data is written to the DR database to ensure data consistency before and after DR.

The success of DR depends on environment and manual operations. To ensure a smooth DR, perform a DR trial before you start the DR task to help you detect and resolve problems in advance.
It is recommended that you start your DR task during off-peak hours to minimize the impact on your services.
- If the bandwidth is not limited, initialization of DR will increase query workload of the source database by 50 MB/s and occupy 2 to 4 vCPUs.
- To ensure data consistency, tables without a primary key may be locked for 3s during disaster recovery.
- The data in the DR process may be locked by other transactions for a long period of time, resulting in read timeout.
- 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 DR, the exclusive lock on that table may be blocked.
Data-Level Comparison
To obtain accurate comparison results, start data comparison 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, data inconsistency may occur, reducing the reliability and validity of the comparison results.

Precautions

Before creating a DR task, read the following precautions:

Table 3 Precautions
Type	Constraint
Disaster recovery objects	Only MyISAM and InnoDB tables support disaster recovery. System tables are not supported. Triggers and events do not support disaster recovery. Accounts that have operation permissions on customized objects in the system database cannot be used for disaster recovery. Disaster recovery cannot be configured for a specific service database. Disaster recovery for non-standard floating-point data that can be written in loose mode but cannot be written in strict mode is not supported. Such non-standard floating-point data may fail to be hit, causing data disaster recovery failures.
Service database configuration	During data disaster recovery, do not upgrade the MySQL instance across major versions. Otherwise, data may become inconsistent or the synchronization task may fail (data, table structures, and keywords may cause compatibility changes after the cross-version upgrade). You are advised to create a DR task again if the MySQL instance is upgraded across major versions. The binlog of the MySQL service database must be enabled and use the row-based format. If the storage space is sufficient, store the service database binlog for as long as possible. The recommended retention period is seven days. For self-built MySQL databases, you can set the expire_logs_days parameter to specify the binlog retention period. If the source database is an RDS for MySQL instance, set the binlog retention period by following the instructions provided in RDS User Guide. The service database username or password cannot be empty. server_id in the MySQL service database must be set. If the service database version is MySQL 5.6 or earlier, the server_id value ranges from 2 to 4294967296. If the service database is MySQL 5.7 or later, the server_id value ranges from 1 to 4294967296. During disaster recovery, if the session variable character_set_client is set to binary, some data may include garbled characters. GTID must be enabled for the database. During the disaster recovery, 0 cannot be written to the auto-increment primary key column in the service database. Otherwise, the data of the auto-increment column in the service database is inconsistent with that in the DR database. The service database name must contain 1 to 64 characters, including only lowercase letters, digits, hyphens (-), and underscores (_). The table name and view name in the service database cannot contain non-ASCII characters, or the following characters: .'<>/\" The column names in the service database tables cannot end with a backslash (\). If the expire_logs_days value of the service database is set to 0, the disaster recovery may fail. If tables that have no primary key contain hidden primary keys in the service database, the DR task may fail or data may be inconsistent.
DR database configuration	During data disaster recovery, do not upgrade the MySQL instance across major versions. Otherwise, data may become inconsistent or the synchronization task may fail (data, table structures, and keywords may cause compatibility changes after the cross-version upgrade). You are advised to create a DR task again if the MySQL instance is upgraded across major versions. The DR DB instance is running properly. If the DR DB instance is a primary/standby instance, the replication status must also be normal. The DR DB instance must have sufficient storage space. The major version of the DR database must be the same as that of the service database. The binlog of the DR database must be enabled and use the row-based format. GTID must be enabled for the DR database. The DR DB instance cannot contain any service databases except the MySQL system database. If you select an RDS DB instance on the console as the DR database, the DR instance will be set to read-only after the DR task starts.
Precautions	If a physically generated column in a table is generated based on a time type, the data in the column may be inconsistent. Cascade operations cannot be performed on tables with foreign keys. If the foreign key index of a table is a common index, the table structure may fail to be created. You are advised to use a unique index. The service database does not support point-in-time recovery (PITR). Binlogs cannot be forcibly deleted. Otherwise, the DR task fails. The service database does not support the reset master or reset master to command, which may cause DRS task failures or data inconsistency. If the network is reconnected within 30 seconds, disaster recovery will not be affected. If the network is interrupted for more than 30 seconds, the DR task will fail. Resumable upload is supported, but data may be repeatedly inserted into a table that does not have a primary key. If there is a DR task in a database, you are not allowed to create a migration or synchronization task (The database cannot be used as the source or destination database of the migration or synchronization task). The parameter modification of the service database is not recorded in logs and is not synchronized to the DR database. Therefore, you need to modify the parameters after the DR database is promoted to the primary. If the service database and DR database are RDS for MySQL instances, tables with TDE enabled cannot be created. If the DR database version is 5.7, the last digit 0 after the decimal point is lost in the floating point number of the JSON type due to version restrictions. The value comparison result will be inconsistent due to precision loss. Before creating a DRS task, if concurrency control rules of SQL statements are configured for the service or DR database, the DRS task may fail. DB instances that you need to enter their IP addresses are external databases. If a high-privilege user created in an external database is not supported by RDS for MySQL, the user will not be synchronized to the DR database, for example, the super user. If the external database does not provide the superuser permission, it cannot be set to read-only when it acts as a standby database. Ensure that the data of the standby node is synchronized only from the primary node. Any other write operations will pollute the data in the standby database, data conflicts may occur in the DR center and cannot be resolved. If the external database is a standby and read-only database, only the account with the superuser permission can write data to that database. But you still need to ensure that data is written only by this account. Otherwise, the standby database may be polluted, and data conflicts occur in the DR center and cannot be resolved. During disaster recovery, if the password of the service database is changed, the DR task will fail. To rectify the fault, you can correct the service database information on the DRS console and retry the task to continue disaster recovery. Generally, you are advised not to modify the preceding information during disaster recovery. If the service database port is changed during disaster recovery, the DR task fails. Generally, you are advised not to modify the service database port during disaster recovery. During disaster recovery, if the service database is on an RDS DB instance that does not belong the current cloud platform, the IP address cannot be changed. If the service database is an RDS instance on the current cloud and the DR task fails due to changes on the IP address, DRS automatically changes the IP address to the correct one. Then, you can retry the task to continue disaster recovery. Therefore, changing the IP address is not recommended. During disaster recovery, you can create accounts for the service database. During the DR initialization, do not perform DDL operations on the source database. Otherwise, the DR task may be abnormal. Do not write data to the source database during the primary/standby switchover. Otherwise, data pollution or table structure inconsistency may occur, resulting in data inconsistency between the service database and DR database.

Procedure

On the Disaster Recovery Management page, click Create Disaster Recovery Task.

On the Create Disaster Recovery Instance page, specify the task name, description, and the DR instance details, and click Create Now.

Task information description

Table 4 Task and recipient description
Parameter	Description
Task Name	The task name must start with a letter and consist of 4 to 50 characters. It can contain only letters, digits, hyphens (-), and underscores (_).
Description	The description consists of a maximum of 256 characters and cannot contain special characters !=<>'&"\

DR instance information

Table 5 DR instance settings
Parameter	Description
Disaster Recovery Relationship	Select Current cloud as standby. By default, Current cloud as standby is selected. You can also select Current cloud as active. Current cloud as standby: The DR database is on the current cloud. Current cloud as active: The service database is on the current cloud.
Service DB Engine	Select MySQL.
DR DB Engine	Select MySQL.
Network Type	The public network is used as an example. Available options: VPN or Direct Connect and Public network. By default, the value is Public network.
DR DB Instance	RDS DB instance you have created as the destination database of the DR task.
Disaster Recovery Instance Subnet	Select the subnet where the disaster recovery instance is located. You can also click View Subnets to go to the network console to view the subnet where the instance resides. By default, the DRS instance and the DR DB instance are in the same subnet. You need to select the subnet where the DRS instance resides and ensure that there are available IP addresses. To ensure that the disaster recovery instance is successfully created, only subnets with DHCP enabled are displayed.
Destination DB Instance Access	Select Read-only. During disaster recovery, the entire DR database instance becomes read-only. To change the DR database to Read/Write, you can change the DR database (or destination database) to a service database by clicking Promote Current Cloud on the Disaster Recovery Monitoring tab. If a DR task fails, the DR database does not automatically change to the read/write state. If a DR task is paused, you can disable read-only for the DR database. For details, see Disabling or Enabling Read-Only. After read-only is disabled and the DR task is resumed, the DR database automatically changes to read-only. The read-only settings of the DR DB instance are also affected by the access settings of the DB instance itself. Therefore, you are advised not to set the access settings of the DB instance on the RDS console. After the DR task is complete, the DR database changes to Read/Write. When the external database functions as the DR database, the user with the superuser permission can set the database to read-only. If a DRS instance node is rebuilt due to a fault, to ensure data consistency during the DRS task restoration, the current cloud standby database is set to read-only before the task is restored. After the task is restored, the synchronization relationship recovers.
Enable Binlog Cleanup	This parameter is available when you set Disaster Recovery Relationship to Current cloud as standby. It indicates whether to enable the function of quickly clearing binlogs of the destination database. After this function is enabled, binlog clearing is enabled for the DR database during the full synchronization and disabled during the incremental synchronization.
Specify EIP	This parameter is available when you select Public network for Network Type. Select an EIP to be bound to the DRS instance. DRS will automatically bind the specified EIP to the DRS instance and unbind the EIP after the task is complete. The number of specified EIPs must be the consistent with that of DB instances.

Specifications

Table 6 Specifications
Parameter
Description
AZ
Select the AZ where you want to create the DRS task. Selecting the one housing the source or destination database can provide better performance.

Table 6 Specifications
Parameter	Description
AZ	Select the AZ where you want to create the DRS task. Selecting the one housing the source or destination database can provide better performance.

Enterprise Project and Tags

Table 7 Enterprise Project and Tags
Parameter	Description
Enterprise Project	An enterprise project you would like to use to centrally manage your cloud resources and members. Select an enterprise project from the drop-down list. The default project is default.
Tags	Tags a task. This configuration is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 20 tags. After a task is created, you can view its tag details on the Tags tab. For details, see Tag Management.

Note

If a task fails to be created, DRS retains the task for three days by default. After three days, the task automatically stops.

On the Configure Source and Destination Databases page, wait until the DR 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 DR instance. After the connection tests are successful, select the check box before the agreement and click Next.

Select Current cloud as standby for Disaster Recovery Relationship in 2.

Table 8 Service database settings
Parameter	Description
Database Type	By default, Self-built on ECS is selected.
IP Address or Domain Name	The IP address or domain name of the service database.
Port	The port of the service database. Range: 1 – 65535
Database Username	The username for accessing the service database.
Database Password	The password for the service 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, Initializing, Disaster recovery in progress, or Disaster recovery failed status, in the Connection Information area on the Basic Information tab, click Modify Connection Details. In the displayed dialog box, change the password.

Note

The IP address, domain name, username, and password of the service database are encrypted and stored in DRS and will be cleared after the task is deleted.

Table 9 DR database settings
Parameter	Description
DB Instance Name	The DB instance you selected when creating the DR task and cannot be changed.
Database Username	The username for accessing the DR database.
Database Password	The password for the database username. The password can be changed after a task is created. If the task is in the Starting, Initializing, Disaster recovery in progress, or Disaster recovery failed status, in the DR Information area on the Basic Information tab, click Modify Connection Details. In the displayed dialog box, change the password. The database username and password are encrypted and stored in DRS, and will be cleared after the task is deleted.
SSL Connection	If SSL connection is required, enable SSL on the DR database, ensure that related parameters have been correctly configured, and upload an SSL certificate. NOTE: The maximum size of a single certificate file that can be uploaded is 500 KB. If SSL is disabled, your data may be at risk.

Select Current cloud as active for Disaster Recovery Relationship in 2.

Table 10 Service database settings
Parameter	Description
DB Instance Name	The RDS instance selected when you created the DR task. This parameter cannot be changed.
Database Username	The username for accessing the service 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, Initializing, Disaster recovery in progress, or Disaster recovery failed status, in the DR Information area on the Basic Information tab, click Modify Connection Details. In the displayed dialog box, change the password. The database username and password are encrypted and stored in the system and will be cleared after the task is deleted.
SSL Connection	If SSL connection is required, enable SSL on the service database, ensure that related parameters have been correctly configured, and upload an SSL certificate. NOTE: The maximum size of a single certificate file that can be uploaded is 500 KB. If SSL is disabled, your data may be at risk.

Table 11 DR database settings
Parameter	Description
Database Type	By default, Self-built on ECS is selected. The destination database can be a Self-built on ECS or an RDS DB instance. If you select RDS DB instance, you need to select the region where the destination database is located.
IP Address or Domain Name	The IP address or domain name of the DR database.
Port	The port of the DR database. Range: 1 – 65535
Region	The region where the RDS DB instance is located. This parameter is available only when the destination database is an RDS DB instance.
DB Instance Name	DR instance name. This parameter is available only when the destination database is an RDS DB instance. NOTE: When the DB instance is used as the DR database, it is set to read-only. After the task is complete, the DB instance can be readable and writable.
Database Username	Username for logging in to the DR database.
Database Password	Password for the database username.

Note

The IP address, domain name, username, and password of the DR database are encrypted and stored in DRS and will be cleared after the task is deleted.

On the Configure DR page, specify flow control and click Next.

Table 12 DR settings
Parameter	Description
Flow Control	You can choose whether to control the flow. Yes You can customize the maximum disaster recovery speed. During the disaster recovery, the speed of each task (or each subtask in multi-task mode) does not exceed the value of this parameter. 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 Always. A maximum of 10 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 DR speed is not limited and the outbound bandwidth of the source database is maximally used, which causes read consumption on the source database accordingly. 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 in the DR initialization phase. You can also change the flow control mode when the task is in the Configuration state. For details, see Modifying the Flow Control Mode.
Migrate Definer to User	Indicates whether to migrate the Definers of all source database objects to the destination database user entered during the connection test. 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. Note that if the Definer account is not found in the destination database, unavailable objects will be created.

On the Check Task page, check the DR task.
- If any check fails, review the failure 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%, go to the Compare Parameter page.
  Note
  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.

On the Confirm Task page, specify Start Time. After confirming that the configured information about the DR task is correct, click Submit.

Table 13 Task settings
Parameter	Description
Start Time	Set Start Time to Start upon task creation or Start at a specified time based on site requirements. NOTE: Starting a DR task may slightly affect the performance of the service and DR databases. You are advised to start a DR task during off-peak hours.

After the task is submitted, view and manage it on the Disaster Recovery 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.
- By default, DRS retains a task in the Configuration state for three days. After three days, DRS automatically deletes background resources, but the task status remains unchanged. When you reconfigure the task, DRS applies for resources again.
- For a public network task, DRS needs to delete background resources after you stop the task. The EIP bound to the task cannot be restored to the Unbound state until background resources are deleted.
- For a task that is in the Disaster recovery in progress state, you can use data comparison to check whether data is consistent before and after the disaster recovery.

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