From MySQL to GaussDB Distributed

Supported Source and Destination Databases

**Table 1** Supported databases
Source DB	Destination DB
On-premises MySQL databases MySQL databases on an ECS MySQL databases on other clouds RDS for MySQL	GaussDB distributed

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 synchronization, 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 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 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.
- 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.
- 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, data inconsistency may occur, reducing the reliability and validity of the comparison results.

Precautions

Before creating a synchronization task, read the following notes:

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 source or destination databases, modify the connection information in the DRS task as soon as possible to prevent automatic retry after a task failure. Automatic retry will lock the database accounts.

**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 GaussDB database user must have the following permissions: Database-level permissions: Log in to the postgres base database as user root or other DATABASE users with the Sysadmin role, and grant the CREATE and CONNECT permissions to user DATABASE. Schema-level permission: Log in to the database as user root or user DATABASE with the Sysadmin role, or the owner of the object, and grant the CREATE and USAGE permissions of the schema to the user. Table-level permission: Log in to the database as user root or user DATABASE with the Sysadmin role, or the owner of the object, and grant the SELECT, UPDATE, INSERT, ALTER, INDEX, and DELETE permissions for all tables in the SCHEMA to the user.
Synchronization object	Only tables can be synchronized. Other database objects such as stored procedures cannot be synchronized. Only tables with primary keys can be synchronized. Tables without primary keys cannot be synchronized. Incremental synchronization does not support synchronization of DDL. MySQL tables containing virtual columns cannot be synchronized. The following data types are not supported: XML, JSON, geometry, point, lineString, polygon, geometrycollection, multipoint, multilinestring, and multipolygon. Tables with storage engine different to MyISAM and InnoDB cannot be synchronized.
Source database	During the incremental synchronization, the binlog of the source 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 this period is set to 0, the synchronization may fail. If the source database is an on-premises MySQL database, set expire_logs_days to specify the binlog retention period. Set expire_logs_day 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. If the source database is an RDS for MySQL instance, set the binlog retention period by following the instructions provided in RDS User Guide. GTID must be enabled 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. For MySQL 5.7, the value of server_id ranges from 1 to 4294967296. The names of the source databases and tables cannot contain non-ASCII characters, or special characters .<'>/\
Destination database	The destination DB instance is running properly. The destination DB instance must have sufficient storage space. The time zone of the destination database must be the same as that of the source database. The mapped database configured for the task must exist in the destination database.
Precautions	If the DCC does not support instances with 4 vCPUs and 8 GB memory or higher instance specifications, the synchronization task cannot be created. Cascading one-way synchronization is not supported. For example, data cannot be synchronized from instance A to instance B and then from instance B to instance C. If the network is reconnected within 30 seconds, real-time synchronization will not be affected. If the network is interrupted for more than 30 seconds, the synchronization task will fail. If the character sets of the source and destination databases are different, data may be inconsistent or synchronization may fail. If the data types are incompatible, the synchronization may fail. After a table in the source database is synchronized to the destination database, the table is distributed in hash mode and cannot be replicated. If the source DB instance is an RDS for MySQL instance, tables encrypted using Transparent Data Encryption (TDE) cannot be synchronized. If the source 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 5.7.0 and 5.7.28), you need to submit an O&M application for testing the SSL connection. 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 changes to the source database cannot be synchronized to the destination database in multiple tasks at the same time. Otherwise, data inconsistency and synchronization failure may occur. In a full synchronization for the table structure, the length of char, varchar, nvarchar, enum, and set characters in the source database automatically increases by byte in the destination database (because the length of the destination database is in the unit of byte). The increase multiple depends on the character set of columns in the source database. For example, if the character set of the source database is UTF8, increase the length (byte) by three times. If the character set of the source database is UTF8MB4, increase the length (byte) by four times. During an incremental synchronization, do not modify or delete the usernames, passwords, permissions, or ports of the source and destination databases. During an incremental synchronization, DDLs of the source database cannot be replicated. During an incremental synchronization, do not perform the restoration operation on the source database. During task startup or full synchronization, you are not advised to perform DDL operations, such as the deletion operation. Otherwise, the task may fail. 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 source database cannot be restored. The source database does not support the reset master or reset master to command, which may cause DRS task failures or data inconsistency. Do not use an imprecise value type as the primary key in the database. This feature affects the synchronization of UPDATE and DELETE statements in the DRS incremental scenario. If tables without primary keys contain large fields (BLOB, TEXT, CLOB, NCLOB, or BYTEA), data of the large fields may be inconsistent during incremental synchronization. Floating-point data is approximate numbers and depends on the OS platform and underlying implementation. FLOAT and DOUBLE data is inaccurate. If you synchronize floating-point data between MySQL and GaussDB, there may be some differences. For details, see the official MySQL documentation. Two-phase commit is not supported. The ongoing synchronization task cannot be paused. Data processing is not supported. If the source table to be synchronized has the AUTO_INCREMENT attribute, DRS automatically updates the start value of the GaussDB auto-increment sequence corresponding to the integer sequence of the table when the task is complete. The updated value is the maximum value of the sequence plus 10,000.

Procedure

This section uses real-time synchronization from MySQL to GaussDB distributed as an example to describe how to configure a real-time synchronization task.

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

On the Create Synchronization Instance page, select a region and project, specify the task name, description, and the synchronization instance details, and click Create Now.

Task information description

Figure 1 Synchronization task information

**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 !=<>'&"\

Synchronization instance details

Figure 2 Synchronization instance details

**Table 4** Synchronization instance settings
Parameter	Description
Data Flow	Select To the cloud.
Source DB Engine	Select MySQL.
Destination DB Engine	Select GaussDB Distributed.
Network Type	The Public network is used as an example. Available options: VPC, Public network and VPN or Direct Connect
Destination DB Instance	An available GaussDB distributed instance.
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.
Synchronization mode	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.

Enterprise Projects and Tags

Figure 3 Enterprise projects and tags

**Table 5** Enterprise Projects and Tags
Parameter	Description
Enterprise Project	An enterprise project you would like to use to centrally manage your Global Accelerator resources. Select an enterprise project from the drop-down list. The default project is default. For more information about enterprise project, see Enterprise Management User Guide. To customize an enterprise project, click Enterprise in the upper right corner of the console. The Enterprise Management page is displayed. For details, see Creating an Enterprise Project in Enterprise Management 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.

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.

Figure 4 Source database information

**Table 6** 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 SSL is not enabled, your data may be at risk.

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

Figure 5 Destination database information

**Table 7** Destination database settings
Parameter	Description
DB Instance Name	The GaussDB distributed DB instance selected during synchronization task creation. This parameter cannot be changed.
Database Username	The username for accessing the destination database.
Database Password	The database username and password are encrypted and stored in the system and will be cleared after the task is deleted.

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

Figure 6 Synchronization mode

**Table 8** Synchronization mode and object
Parameter	Description
Incremental 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.
Synchronization Object	The left pane displays the source database objects, and the right pane displays the selected objects. You can select table-level synchronization based on your service requirements. If the synchronization objects in source and destination databases have different names, you can map the source object name to the destination one. For details, see Mapping Object Names. 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.
  For details about how to handle check failures, see Checking Whether the Source Database Is Connected in Data Replication Service User Guide.
- If all check items are successful, click Next.
  Figure 7 Pre-check
  
  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, Send Notification, SMN Topic, Synchronization Delay Threshold, and Stop Abnormal Tasks After, confirm that the configured information is correct, select the check box before the agreement, and click Submit to submit the task.

Figure 8 Task startup settings

**Table 9** 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.
Send Notifications	SMN topic. This parameter is optional. If an exception occurs during synchronization, 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 synchronization, 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: If the delay threshold is set to 0, no notifications will be sent to the recipient. In the early stages of an incremental synchronization, the synchronization delay is long because a large quantity of data is awaiting synchronization. In this case, no notifications will be sent. Before setting the delay threshold, enable Send Notification.
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.

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.
- By default, DRS retains a task in the Configuration state for three days. After three days, DRS automatically deletes background resources, and the task status remains unchanged. When you restart the task configuration, DRS applies for resources again.