Help Center/ Data Replication Service/ Real-Time Synchronization/ To the Cloud/ From Microsoft SQL Server to GaussDB(DWS)

Updated on 2023-04-26 GMT+08:00

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From Microsoft SQL Server to GaussDB(DWS)

Supported Source and Destination Databases

**Table 1** Supported databases
Source DB	Destination DB
On-premises Microsoft SQL Server (Enterprise Edition 2012 or later, Standard Edition 2016 SP1 or later) Microsoft SQL Server database on an ECS (Enterprise Edition 2012 or later, Standard Edition 2016 SP1 or later) Microsoft SQL Server database on other clouds (Enterprise Edition 2012 or later, Standard Edition 2016 SP1 or later) RDS for SQL Server (Enterprise Edition 2012 or later, Standard Edition 2016 SP1 or later)	GaussDB(DWS) cluster

Only whitelisted users can use this function.

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.

**Table 2** Supported synchronization objects
Type	Precautions
Objects	Supported field types: TINYINT, SMALLINT, INT, BIGINT, DECIMAL, NUMERIC, FLOAT, REAL, SMALLMONEY, MONEY, BIT, DATE, DATETIME, DATETIME2, DATETIMEOFFSET, TIME, TIMESTAMP, XML, CHAR, VARCHAR, NCHAR, NVARCHAR, BINARY, VARBINARY, IMAGE, HIERARCHYID, NTEXT, TEXT, and UNIQUEIDENTIFIER Unsupported field types: SQL_VARIANT, GEOMETRY, and GEOGRAPHY Scope of full synchronization Structures, data, and indexes of a table are supported. A database or table name can contain a maximum of 64 characters, including only letters, digits, underscores (_), and hyphens (-). The number of tables selected for the synchronization object cannot exceed 1000. If there are more than 1000 tables, you are advised to synchronize them in batches. (Create a new task after the synchronization task is complete.) Transparent Data Encryption (TDE) encrypted databases in the source instance cannot be synchronized. If you do not need to synchronize TDE encrypted databases, deselect them. If you need to synchronize TDE encrypted databases, disable TDE first. Column encryption is not supported. Scope of incremental synchronization DML statements, including INSERT, UPDATE, and DELETE, are supported DDL statements are not supported.

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.

**Table 3** Database account permission
Type	Full+Incremental Synchronization
Source database user	Sysadmin or view server state and db_datareader or db_owner permissions for databases to be synchronized
Destination database user	If the destination instance does not contain the database to be synchronized, the CREATEDB permission is required. If the destination instance contains databases but does not have schemas, the CONNECT and CREATE permissions for the databases are required. If the destination instance contains databases and schemas but does not contain tables, the CONNECT permission for databases and the USAGE and CREATE permissions for schemas are required. If the destination instance contains databases, schemas, and tables, the CONNECT permission for databases, the USAGE permission for schemas, and the INSERT, UPDATE, DELETE, SELECT, ALTER, REFERENCES, and INDEX permissions for tables are required.

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.
- 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

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

**Table 4** Precautions
Type	Constraints
Starting a task	Source database parameter requirements: The source database mode must be set to FULL. The SQL Server Agent proxy service must be enabled for the source database. If Force Protocol Encryption is set to Yes for the source database, Trust Server Certificate also must be set to Yes, as shown in Figure 1. Figure 1 Client configuration Source database object requirements: If the source database contains disabled clustered indexes of tables, the synchronization fails. The source database cannot contain the username cdc or schema. The database name can contain a maximum of 64 characters, including only letters, digits, underscores (_), and hyphens (-). The table name in the source database cannot contain special characters '<>" Destination database object requirements: The destination DB instance must have sufficient storage space. The destination DB instance cannot contain databases with the same name as the source database (except SQL Server system databases). 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. Other notes: Do not perform primary/standby switchover on the source database. Otherwise, the synchronization task will fail. Incremental synchronization of the source SQL Server database is based on the CDC capability provided by the SQL Server database. If CDC of the source SQL Server database is abnormal (for example, CDC is disabled or the transaction log is full), incremental synchronization will be affected.
Full synchronization	Do not change the port of the source and destination databases, or change or delete the passwords and permissions of the source and destination database users. Otherwise, the task may fail. Do not run any DDL statement in the source database. Otherwise, data may be inconsistent or the task may fail. Do not write data to the destination database. Otherwise, data may be inconsistent.
Incremental synchronization	Do not change the port of the source and destination databases, or change or delete the passwords and permissions of the source and destination database users. Otherwise, the task may fail. Do not write data to the destination database. Otherwise, data may be inconsistent. DDL operations performed on the source database will not be synchronized to the destination database. The IMAGE, TEXT, and NTEXT big data types cannot be deleted. You can add additional synchronization objects.
Synchronization comparison	You are advised to compare data in the source database during off-peak hours to prevent inconsistent data from being falsely reported and reduce the impact on the source database and DRS tasks. During incremental synchronization, if data is written to the source database, the comparison results may be inconsistent. Data cannot be compared during full synchronization. Do not limit the synchronization speed during data comparison.

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 Microsoft SQL Server to GaussDB(DWS) synchronization as an example to describe how to use DRS to configure a real-time synchronization task over a public network.

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 2 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 3 Synchronization instance details

**Table 6** Synchronization instance settings
Parameter	Description
Data Flow	Select To the cloud.
Source DB Engine	Select Microsoft SQL Server.
Destination DB Engine	Select GaussDB(DWS).
Network Type	Available options: VPC, Public network and VPN or Direct Connect. Public network 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 Projects and Tags

Figure 4 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.

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 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 5 Source database information

**Table 8** Source database settings
Parameter	Description
IP Address or Domain Name	The IP address or domain name of the source Microsoft SQL Server database.
Port	The port of the source database. Range: 1 – 65535
Database Username	The username for logging in to the source Microsoft SQL Server 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.

Figure 6 Destination database information

**Table 9** Destination database settings
Parameter	Description
DB Instance Name	The GaussDB(DWS) instance that you selected during task creation and 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.

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

Figure 7 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 8 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.
Synchronization Object Type	Available options: Table structure, Data, and Constraint Data is selected by default. If Table structure is selected, the destination database cannot contain tables whose names are the same as the source tables to be synchronized. If Table structure is not selected, the destination database must have tables that match the source tables, and the table structure must be the same as the selected source table structures.
Synchronization Object	The left pane displays the source database objects, and the right pane displays the selected objects. DRS supports table-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. The number of tables selected for the synchronization object cannot exceed 1000. If there are more than 1000 tables, you are advised to synchronize them in batches. (Create a new task after the synchronization task is complete.) 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 9 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 10 Task startup settings

**Table 11** 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.