Supported Source and Destination Databases

**Table 1** Supported databases
Source DB	Destination DB
On-premises MySQL databases MySQL databases on an ECS	On-premises MySQL databases MySQL databases on an ECS

Prerequisites

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

Suggestions

When a task is being started or in the full synchronization phase, do not perform DDL operations on the source database. Otherwise, the task may be abnormal.
To keep data consistency before and after the synchronization, ensure that no data is written to the destination database during the synchronization.

The success of database synchronization depends on environment and manual operations. To ensure a smooth synchronization, perform a synchronization trial before you start the synchronization to help you detect and resolve problems in advance.
Start your synchronization task during off-peak hours. A less active database is easier to synchronize successfully. If the data is fairly static, there is less likely to be any severe performance impacts during the synchronization. If you have to synchronize data during peak hours, you can select Yes for Flow Control to adjust the synchronization speed.
- If network bandwidth is not limited, the query rate of the source database increases by about 50 MB/s during full synchronization, and two to four CPUs are occupied.
- To ensure data consistency, tables to be synchronized without a primary key may be locked for 3s.
- The data being synchronized may be locked by other transactions for a long period of time, resulting in read timeout.
- Due to the inherent characteristics of MySQL, in certain 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%.
- When 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, data inconsistency may occur, reducing the reliability and validity of the comparison results.
For many-to-one synchronization tasks that involve the synchronization of the same table, DDL operations cannot be performed on source databases. Otherwise, all synchronization tasks fail.

Precautions

Before creating a synchronization task, read the following notes:

**Table 2** Precautions
Type	Restrictions
Database permissions	The source database user must have the following permissions: SELECT, SHOW VIEW, EVENT, LOCK TABLES, REPLICATION SLAVE, and REPLICATION CLIENT. The destination database user must have the following permissions: SELECT, CREATE, DROP, DELETE, INSERT, UPDATE, ALTER, and REFERENCES.
Synchronization object	Only tables, primary key indexes, unique indexes, common indexes, store procedures, views, and functions can be synchronized. During database mapping, the source database cannot contain stored procedures, views, or functions. The databases to be mapped to the destination can only contain tables during synchronization. Otherwise, the synchronization task fails. If the database table name contains characters other than letters, digits, and underscores (_), or the mapped database table name contains hyphens (-) and number signs (#), the name length cannot exceed 42 characters. Tables with storage engine different to MyISAM and InnoDB cannot be synchronized. For an incremental synchronization task, ensure that the synchronization objects exist in the destination database.
Source database	During the incremental synchronization, the binlog of the source MySQL database must be enabled and use the row-based format. If the storage space is sufficient, store the source database binlog for as long as possible. The recommended retention period is three days. If the expire_logs_days value of the source database is set to 0, the synchronization may fail. Enable GTID for the source database. If GTID is not enabled for the source database, primary/standby switchover is not supported. DRS tasks will be interrupted and cannot be restored during a switchover. During an incremental synchronization, the server_id value of the MySQL source database must be set. If the source database version is MySQL 5.6 or earlier, the server_id value ranges from 2 to 4294967296. If the source database is MySQL 5.7 or later, the server_id value ranges from 1 to 4294967296. The source database names cannot contain non-ASCII characters, or the following characters: '<`>/\ The table and view names in the source database cannot contain non-ASCII characters, or special characters '<>/\ The source database name or mapped name cannot start with ib_logfile or be ib_buffer_pool, ib_doublewrite, ibdata1 or ibtmp1. Tables with storage engine different to MyISAM and InnoDB cannot be synchronized to RDS. Database mapping does not support views or stored procedures. If the source database contains views or stored procedures, the synchronization may fail.
Destination database	Data cannot be synchronized from a newer version database to an older version database. The destination DB instance is running properly. If the destination DB instance type is primary/standby, the replication status must also be normal. The destination DB instance must have sufficient storage space. If the destination database (excluding MySQL system database) has the same name as the source database, the table structures in the destination database must be consistent with those in the source database. The character set of the destination database must be the same as that of the source database. The time zone of the destination database must be the same as that of the source database. During a synchronization, a large amount of data is written to the destination database. If the value of the max_allowed_packet parameter of the destination database is too small, data cannot be written. You are advised to set the max_allowed_packet parameter to a value greater than 100 MB. If the MyISAM tables are included in the synchronization objects, the sql_mode parameter in the destination database cannot contain the no_engine_substitution parameter. Otherwise, the synchronization fails. The source database names mapped to the destination database cannot contain the following characters: dots (.), angle brackets (<>), backslash (\), and single quotation marks (')
Precautions	Objects that have dependencies must be synchronized at the same time to avoid synchronization failure. Common dependencies: tables referenced by views, views referenced by views, views and tables referenced by stored procedures/functions/triggers, and tables referenced by primary and foreign keys Only MySQL to MySQL synchronization supports many-to-one synchronization. During table-level many-to-one synchronization, tables without primary keys cannot exist in the source database. If the source or 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. The destination table can contain more columns than the source table. However, the following failures must be avoided: Assume that extra columns on the destination cannot be null or have default values. If newly inserted data records are synchronized from the source to the destination, the extra columns will become null, which does not meet the requirements of the destination and will cause the task to fail. Assume that extra columns on the destination must be fixed at a default value and have a unique constraint. If newly inserted data records are synchronized from the source to the destination, the extra columns will contain multiple default values. That does not meet the unique constraint of the destination and will cause the task to fail. The source database does not support point-in-time recovery (PITR). The destination database cannot be restored to a point in time when a full synchronization was being performed. 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. Binlogs cannot be forcibly deleted. Otherwise, the synchronization task fails. The source database does not support the reset master or reset master to command, which may cause DRS task failures or data inconsistency. Set the expire_log_day parameter to a proper value to ensure that the binlog does not expire before data transfer resumes. This ensures that services can be recovered after interruption. After a task is created, the destination database cannot be set to read-only. A real-time synchronization task may fail due to the change of the username and password of the source or destination database. If it happens, rectify the information and then retry the synchronization task on the DRS console. Generally, you are advised not to modify the preceding information during synchronization. If the source or destination database port is changed during data synchronization, the synchronization task fails. You can rectify the fault as follows: If the source database port is wrong, correct the port number on the DRS console and then retry the synchronization task. If the destination database port is wrong, DRS automatically changes the port to the correct one, and then you need to retry the synchronization task. Generally, do not modify the port number during synchronization. During real-time synchronization, do not change the IP address. DDL operations are not supported during full synchronization. Data inconsistency may occur when the MyISAM table is modified during a full synchronization. In a full plus incremental synchronization task, the source database cannot contain a table with the same name as a table without a primary key in the destination database. For an incremental synchronization task, if the synchronization point is not precise, data inconsistency may occur. During table-level incremental synchronization, only DDL operations on tables are allowed. During an incremental synchronization of table-level objects, renaming tables is not recommended. For an incremental synchronization task, the start point must be in the standard format. You can run the show master status command in the source database to obtain the start point. If GTID mode is disabled, the format of the start point is File:Position (for example, mysql-bin.014734:8937). After the GTID is enabled, the format of the start point is File:Position. Executed_Gtid_Set (for example, mysql-bin.014734:8937;ea352a82-e9a0-11ea-b650-fa163e1e82ed:1-23377228, 8404bb4b-cc96-11ea-ae7f-fa163ead1b99:1-59684135)

Procedure

On the Data Synchronization Management page, click Create Synchronization Task.

On the Create Synchronization Instance page, specify the task name, description, and the synchronization instance details, and click Next.

**Table 3** Task and recipient description
Parameter	Description
Region	The region where the synchronization instance is deployed. You can change the region.
Project	The project corresponds to the current region and can be changed.
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 !=<>'&"\

**Table 4** Synchronization instance settings
Parameter	Description
Data Flow	Choose Self-built to self-built.
Source DB Engine	Select MySQL.
Destination DB Engine	Select MySQL.
Network Type	The Public network is used as an example. Available options: Public network and VPN or Direct Connect
Instance Type	DRS instance type. The value can be single or primary/standby. primary/standby: This architecture provides HA, improving the reliability of DRS instances. After the primary and standby instances are created, the DRS creates an active subtask and a standby subtask at the same time. If the task on the active node is abnormal, the DRS automatically starts the task on the standby node to continue the synchronization, improving the reliability of the synchronization task. Single: The single-node deployment architecture is used, which is cost-effective.
VPC	Select an available VPC.
Synchronization Instance Subnet	Select the subnet where the synchronization instance is located. 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 ensure that there are available IP addresses. To ensure that the synchronization instance is successfully created, only subnets with DHCP enabled are displayed.
Security Group	Select a security group. You can use security group rules to allow or deny access to the instance.
Synchronization Mode	Select Incremental. Full+Incremental This synchronization mode allows you to synchronize data in real time. After a full synchronization initializes the destination database, an incremental synchronization parses logs to ensure data consistency between the source and destination databases. NOTE: If you select Full+Incremental, data generated during the full synchronization will be continuously synchronized to the destination database, and the source remains accessible. Incremental Through log parsing, incremental data generated on the source database is synchronized to the destination database. During synchronization, the source database continues to provide services for external systems with zero downtime.
AZ	Select the AZ where you want to create the DRS instance. Selecting the one housing the source or destination database can provide better performance. If Instance Type is set to primary/standby, you can specify Primary AZ and Standby AZ.
Tags	This setting 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.

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

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

**Table 5** Source database settings
Parameter	Description
IP Address or Domain Name	The IP address or domain name of the source database.
Port	The port of the source database. Range: 1 – 65535
Database Username	The username for accessing the source database.
Database Password	The password for the database username.
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.

**Table 6** Destination database settings
Parameter	Description
IP Address or Domain Name	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.
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.

The username and password of the source and destination databases are encrypted and stored in DRS, and will be cleared after the task is deleted.

On the Set Synchronization Task page, select the synchronization policy, objects, and data format, and click Next.

**Table 7** Synchronization mode and object
Parameter	Description
Conflict Policy	The conflict policy refers to the conflict handling policy during incremental synchronization. By default, conflicts in the full synchronization phase are ignored. Select any of the following conflict policies: Ignore The system will skip the conflicting data and continue the subsequent synchronization process. Report error The synchronization task will be stopped and fail. Overwrite Conflicting data will be overwritten.
Filter DROP DATABASE	During real-time synchronization, executing DDL operations on the source database may affect the synchronization performance. To reduce the risk of synchronization failure, DRS allows you to filter out DDL operations. Currently, only the delete operations on databases can be filtered by default. If you select Yes, the database deletion operation performed on the source database is not synchronized during data synchronization. If you select No, related operations are synchronized to the destination database during data synchronization.
Synchronize	Supports index synchronization. You can determine whether to synchronize indexes based on the service requirements.
Start Point	The position where the incremental log was created based on the source log. It allows you to perform resumable data transfer. For an incremental synchronization task, the start point must be in the standard format. You can run the show master status command in the source database to obtain the start point. If GTID mode is disabled, the format of the start point is File:Position (for example, mysql-bin.014734:8937). After the GTID is enabled, the format of the start point is File:Position; Executed_Gtid_Set (for example, mysql-bin.014734:8937;ea352a82-e9a0-11ea-b650-fa163e1e82ed:1-23377228, 8404bb4b-cc96-11ea-ae7f-fa163ead1b99:1-59684135)
Synchronization Object	Select Tables, Databases, or Import object file as required. NOTE: To quickly select the desired database objects, you can use the search function. If there are changes made to the source databases or objects, click in the upper right corner to update the objects to be synchronized. If the object name contains spaces, the spaces before and after the object name are not displayed. If there are multiple spaces between the object name and the object name, only one space is displayed. The name of the selected synchronization object cannot contain spaces.

On the Check Task page, check the synchronization task.
- If any check fails, review the cause and rectify the fault. After the fault is rectified, click Check Again.
- If all check items are successful, 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.

On the displayed page, specify Start Time, 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. NOTE: After a synchronization task is started, the performance of the source and destination databases may be affected. You are advised to start a synchronization task during off-peak hours.

After the task is submitted, you can view and manage it on the Data Synchronization 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.

From MySQL to MySQL

Supported Source and Destination Databases

Prerequisites

Suggestions

Precautions

Procedure