From DDM to DDM

Supported Source and Destination Databases

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.
• You are advised to start your synchronization task during off-peak hours by setting Start Time to Start at a specified time. 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.
  • 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, 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 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 and 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.

Procedure

1. On the Data Synchronization Management page, click Create Synchronization Task.
2. 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 information

     Parameter	Description
     Region	The region where the replication 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 DDM.
     Destination DB Engine	Select DDM.
     Network Type	Public network is used as an example. Available options: Public network, VPC, VPN or Direct Connect VPC is suitable for data synchronization between cloud databases of the same account in the same region. Public network is suitable for data synchronization from on-premises or external cloud databases to the destination databases bound with an EIP. VPN or Direct Connect is suitable for synchronization of data between on-premises databases and cloud databases, between cloud databases of different accounts in the same region, or between cloud databases across regions.
     Destination DB Instance	The DDM instance you created.
     Synchronization Instance Subnet	Select the subnet where the synchronization 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 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 synchronization instance is successfully created, only subnets with DHCP enabled are displayed.
     Synchronization Mode	The synchronization mode supported by a DRS task. Full+Incremental is used as an example. For details about the underlying working principles for full or incremental synchronization, see Product Architecture and Function Principles. 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.
     Source DB Instance Quantity	Specifies the number of DB instances bound to the source DDM database. The default value is 2. The value ranges from 1 to 64. Set this parameter based on the site requirements.

   • Task type
     Figure 3 Task type
     

     Table 5 Task type information

     Parameter	Description
     Specifications	DRS instance specifications. Different specifications have different performance upper limits. For details, see Real-Time Synchronization. NOTE: DRS allows you to upgrade specifications only for single-AZ synchronization tasks. Task specifications cannot be downgraded. For details, see Changing Specifications.
     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
     Figure 4 Enterprise projects and tags
     

     Table 6 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. 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 Project Management Service page is displayed. For details, see Creating an Enterprise Project in Enterprise Management User Guide.
     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. If your organization has configured tag policies for DRS, add tags to tasks based on the policies. If a tag does not comply with the policies, task creation may fail. Contact your organization administrator to learn more about tag policies. 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 stops.

3. 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 5 Source database information
   

   Table 7 Source database settings

   Parameter	Description
   Middleware IP Address or Domain Name	The IP address or domain name of the source DDM middleware.
   Port	The port of the source DDM middleware. Value range: 1 to 65535
   Middleware Username	The username of the source DDM instance.
   Middleware Password	The password for the source DDM instance 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 disabled, your data may be at risk.
   DB Instance	The sharded database details.

   

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

   Figure 6 Destination database information
   

   Table 8 Destination database settings

   Parameter	Description
   DB Instance Name	The DDM instance you selected when you create the synchronization task. The instance name 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.

4. On the Set Synchronization Task page, select the objects to be synchronized, and then click Next.
   Figure 7 Synchronization mode
   

   Table 9 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. If you select Ignore, data in the source database may be inconsistent with that in the destination database. Overwrite Conflicting data will be overwritten.
   Synchronization Object	The left pane displays the source database objects, and the right pane displays the selected objects. DRS supports table- and database-level synchronization. You can select data for 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 an object name contains spaces, 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 name of the selected synchronization object cannot contain spaces.

5. 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 Solutions to Failed Check Items in Data Replication Service User Guide.

   • If all check items are successful, click Next.
     Figure 8 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.

6. On the displayed page, specify Start Time, Send Notifications, SMN Topic, Delay Threshold (s), 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 9 Task startup settings
   

   Table 10 Task startup settings

   Parameter	Description
   Start 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	This parameter is optional. After enabled, select a SMN topic. If the status, latency metric, or data of the synchronization task is abnormal, DRS will send a notification.
   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.
   Delay Threshold (s)	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 Notifications.
   Data Exception Notification	This parameter is optional. After enabled, DRS will send a notification if the task data is abnormal.
   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: You can set this parameter only for pay-per-use tasks. 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, 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, but the task status remains unchanged. When you configure the task again, DRS applies for resources for the task again. In this case, the IP address of the DRS instance changes.