From PostgreSQL to GaussDB(DWS)

Supported Source and Destination Databases

Supported Synchronization Objects

Table 2 lists the objects that can be synchronized in different scenarios. DRS will automatically check the objects you selected before the synchronization.

Database Account Permission Requirements

To start a synchronization task, the source and destination database users must meet the requirements in the following table. Different types of synchronization tasks require different permissions. For details, see Table 3. DRS automatically checks the database account permissions in the pre-check phase and provides handling suggestions.

• 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.

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.
  • 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.
  • 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

The full+incremental synchronization process consists of four phases: task startup, full synchronization, incremental synchronization, and task completion. A single full synchronization task contains three phases. To ensure smooth synchronization, read the following notes before creating a synchronization task.

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.

• You have read Suggestions and Precautions.

Procedure

This section uses PostgreSQL to GaussDB(DWS) as an example to describe how to use DRS to configure a real-time synchronization task in the VPC network scenario.

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 5 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 6 Synchronization instance settings

     Parameter	Description
     Data Flow	Select To the cloud.
     Source DB Engine	Select PostgreSQL.
     Destination DB Engine	Select GaussDB(DWS).
     Network Type	Available options: VPC, Public network and VPN or Direct Connect. VPC is used as an example.
     Destination DB Instance	The destination is a GaussDB(DWS) 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.
     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.

   • Enterprise Projects and Tags
     Figure 3 Enterprise projects and tags
     

     Table 7 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.

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.

   Establish the connectivity between the DRS instance and the source and destination databases.

   • Network connectivity: Ensure that the source and destination databases accept connections from the IP address of the DRS instance. To access databases over a public network, configure the database to accept connections from the EIP of the DRS instance. To access databases over a VPC, VPN, or Direct Connect network, configure the database to accept connections from the private IP address of the DRS instance.For details, see Network Preparations.
   • Account connectivity: Ensure that the source and destination databases allows connections from the DRS instance using the username and password.
   

   The source database can be an ECS database or an RDS instance. Configure parameters based on different scenarios.

   • Scenario 1: Databases on an ECS - source database configuration
     Figure 4 Self-build on ECS - source database information
     

     Table 8 Self-build on ECS - source database information

     Parameter	Description
     Source Database Type	Select Self-built on ECS.
     VPC	A dedicated virtual network in which the source database is located. It isolates networks for different services. You can select an existing VPC or create a VPC.
     Subnet	A subnet provides dedicated network resources that are isolated from other networks, improving network security. The subnet must be in the AZ where the source database resides. You need to enable DHCP for creating the source database subnet.
     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 Name	Indicates whether to specify a database. If this option is enabled, enter the database name.
     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.

     

     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.

   • Scenario 2: RDS DB instance - source database configuration
     Figure 5 RDS DB instance - source database information
     

     Table 9 RDS DB instance - source database information

     Parameter	Description
     Source Database Type	Select RDS DB Instance.
     DB Instance Name	Select the RDS PostgreSQL instance to be synchronized as the source DB instance.
     Database Username	The username for accessing the source database.
     Database Password	The password for the database username.

   Figure 6 Destination database information
   

   Table 10 Destination database information

   Parameter	Description
   DB Instance Name	The GaussDB(DWS) instance selected when you created the migration task. This parameter cannot be changed.
   Database Username	The username for accessing the destination database.
   Database Password	The password for the database username.

   

   The username and password of the source and destination databases are encrypted and stored in the databases and the synchronization instance during the synchronization. After the task is deleted, the username and password are permanently deleted.

4. On the Set Synchronization Task page, select the synchronization objects and accounts and click Next.
   Figure 7 Synchronization Mode
   

   Table 11 Synchronization 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.
   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. When you map a schema name or table name to the target object, name the indexes and constraints of the mapped table in the following format: prefix + full name-based hash value + original index/constraint name + _key to prevent index/constraint name conflicts. The prefix of the index is i_, the prefix of the constraint is c_, and the full name is "schema name_table name_index/constraint name". The original index/constraint name may be truncated due to length limitation. 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.

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 Checking Whether the Source Database Is Connected 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 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 9 Task startup settings
   

   Table 12 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.

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, and the task status remains unchanged. When you restart the task configuration, DRS applies for resources again.