From GaussDB Distributed to Oracle

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 User Permission Requirements

Before you 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.
• If a distributed database is the source database, the connectivity of each DN needs to be checked. You are advised to perform data synchronization as a non-root database user to prevent user locking due to incorrect password during DN connection.

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 consists of four phases: task startup, full synchronization, incremental synchronization, and task completion. A single full or incremental 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

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	Choose Self-built to self-built.
     Source DB Engine	Select GaussDB Distributed.
     Destination DB Engine	Select Oracle.
     Network Type	Public network is used as an example. Available options: Public network and VPN or Direct Connect
     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	Available options: Full+Incremental, Full, and Incremental. Full+Incremental is used as an example. 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. Full In this mode, data is synchronized from the source to the destination at a time. Incremental Through log parsing, incremental data generated on the source database is synchronized to the destination database.
     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.
     Source Shard Quantity	The value must be the same as the number of DNs in the distributed source database. Run the following SQL statement to check the value of Source Shard Quantity: SELECT count(DISTINCT node_name) FROM pgxc_node WHERE node_type = 'D';

   • 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, 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 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.
   Figure 4 Source database information
   

   Table 8 Source database settings

   Parameter	Description
   CN IP Address or Domain Name	Enter the IP addresses of GaussDB. Ensure that the entered IP addresses or domain names belong to the same instance.
   Database Username	The username for accessing the source database.
   Database Password	The password for the database username.
   DN IP Address or Domain Name	You can log in to the CN and run the following SQL statement to query the DN IP address: SELECT node_name as dn_name, string_agg(node_host || ':' || node_port, ',' order by node_type) AS dn_ip FROM pgxc_node WHERE node_type != 'C' GROUP BY node_name; The resource types of different database instances are different. Therefore, you are advised to contact O&M personnel.

   

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

   Figure 5 Destination database information
   

   Table 9 Destination database settings

   Parameter	Description
   IP Address or Domain Name	The IP address or domain name of the destination database. NOTE: For a RAC cluster, use a scan IP address and specify Service Name to improve access performance.
   Port	The port of the destination database. Range: 1 - 65535
   Database Service Name	Enter a database service name (Service Name/SID). The client can connect to the Oracle database through the database service name. For details about how to query the database service name, see the prompt on the GUI.
   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 SSL is not enabled, your data may be at risk.

   

   The username and password of the destination database are encrypted and stored in the database 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 objects to be synchronized, and then click Next.
   Figure 6 Synchronization mode
   

   Table 10 Synchronization Object

   Parameter	Description
   Flow Control	You can choose whether to control the flow. Yes You can customize the maximum migration speed. 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 All day. A maximum of three 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. Figure 7 Flow control No The synchronization speed is not limited and the outbound bandwidth of the source database is maximally used, which will increase the read burden on the source database. 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: The flow control mode takes effect only in the full synchronization phase. You can also change the flow control mode after creating a task. For details, see Modifying the Flow Control Mode.
   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. Overwrite Conflicting data will be overwritten.
   Synchronization Object	The left pane displays the source database objects, and the right pane displays the selected objects. You can select Tables or Import object files for Synchronization Object 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. For details about how to import an object file, see Importing Synchronization Objects. 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 Advanced Settings page, set the parameters for full+incremental synchronization selected in 2 and click Next.
   Figure 8 Parameter settings
   

   Table 11 Full synchronization settings

   Parameter	Description	Default Value
   Concurrent Export Tasks	Number of export threads. Value range: 1 to 16. A larger value indicates higher load on the source database.	8
   Concurrent Import Tasks	Number of import threads. Value range: 1 to 16. A larger value indicates higher load on the destination database.	8
   Rows per Shard	Value range: 0 or 520,000 to 1,000,000,000 0 All tables are not sharded, and each table is synchronized as a whole. Other values The table is sharded based on the specified value (or the primary key column). If the number of records in a table is less than the value of this parameter, the table is not sharded.	520000

   Table 12 Incremental synchronization settings

   Parameter	Description	Default Value
   Concurrent Replay Tasks	Number of concurrent threads for data replay. Value range: 1 to 64. Incremental data is concurrently written to the destination database. A larger value indicates higher load on the destination database.	64

6. On the Process Data page, set the filtering rules for data processing.
   • If data processing is not required, click Next.
   • If you need process columns or filter out data, set the corresponding rules by referring to Processing Data.
   Figure 9 Processing data
   

7. 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 10 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.

8. 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 11 Task startup settings
   

   Table 13 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.

9. 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.