From DDS to MongoDB

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB

  • DDS instances

  • On-premises MongoDB databases

  • MongoDB databases on an ECS

  • MongoDB database on other clouds

Prerequisites

  • You have logged in to the DRS console.

  • For details about the DB types and versions supported by real-time synchronization, see Real-Time Synchronization.

Suggestions

  • 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.

  • It is recommended that you start a task during off-peak hours to minimize the impact of synchronization on your services.

Precautions

Before creating a synchronization task, read the following notes:

Note

  • You are advised to create an independent database account for DRS task connection to prevent task failures caused by account 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

Source database (minimum permissions):

  • Permission requirements for incremental synchronization:

    • Replica set: The source database user must have the readAnyDatabase permission for the admin database and the read permission for the local database.

    • Single node: The source database user must have the readAnyDatabase permission for the admin database and the read permission for the local database.

    • Cluster: The source database user must have the readAnyDatabase permission for the admin database and the read permission for the config database.

Minimum permission requirements: The destination database user must have the dbAdminAnyDatabase permission for the admin database and the readWrite permission for the destination database. If the destination database is a cluster instance, the database user must have the read permission for the config database.

Synchronization object

  • Replica set: Only collections (including validator and capped and non-capped collections), indexes, and views can be synchronized.

  • Cluster: Currently, only collections (including validator and capped and non-capped collections), shard keys, indexes, and views can be synchronized.

  • Single node: Only collections (including validator and capped collections), indexes, and views can be synchronized.

  • Collections that contain the _id field without indexes are not supported.

  • The first parameter of BinData() cannot be 2.

  • If ranged sharding is used, maxKey cannot be used as the primary key.

  • If the source database is a cluster database, DBPointer and DBRef are not supported.

Source database

  • During the incremental synchronization, the Oplog of the source database must be enabled.

  • If the storage space is sufficient, store the source database Oplog for as long as possible. The recommended retention period is three days.

  • The source database name cannot contain /\.$ or spaces. The collection name and view name cannot start with system. or contain the dollar sign ($).

Destination database

  • Data cannot be synchronized from a newer version database to an older version database.

  • The destination DB instance is running properly.

  • The destination DB instance must have sufficient storage space.

Precautions

  • If the source is not a cluster instance, the following operations and commands are supported during incremental synchronization:

    • Creating and deleting databases

    • Adding, deleting, and updating documents

    • Creating and deleting collections

    • Creating and deleting indexes

    • Creating and deleting views

    • The convertToCapped, collMod, and renameCollection commands are supported.

  • If the source is a cluster instance:

    • The cluster version cannot be earlier than 4.0.

    • Do not delete synchronization objects in the incremental synchronization phase. Otherwise, the synchronization task will fail.

    • The synchronization process consumes certain CPU and memory resources of the source database. Evaluate the source database resources in advance.

    • If the load on the source database is heavy, the processing speed of change streams cannot keep up with the oplog generation speed. As a result, DRS synchronization delay occurs.

    • Only the following DDLs are supported: drop database, drop collection and rename

    • In the incremental synchronization phase, the synchronization speed can reach up to 10,000 rows in a single table per second.

  • During startup, the specified start point must be within the Oplog range.

  • The destination database user must have the write permission. If the destination is a cluster instance, the database user must have the read permission for the config data.

  • If a Time-to-Live (TTL) index already exists in the collection of the source database or is created during an incremental synchronization, data consistency cannot be ensured when source and destination databases are in different time zone.

  • The value of block_compressor is determined by stats().wiredTiger.creationString.block_compressor of the collection in the source database. If the destination database contains corresponding empty collections, the compression parameters will not be migrated. If the compression parameters in the source database are not supported by the destination database, configure the compression parameters based on net.compression.compressors of the destination database. If the storage engine of the destination database is not WiredTiger, DRS does not synchronize compression parameters.

  • If the destination is a replica set instance out of the cloud, enter information about all primary and secondary nodes to reduce the impact of a primary/secondary switchover on the synchronization task. If you enter information about primary and secondary nodes, ensure that all nodes belong to the same replica set instance.

  • If the destination is a cluster instance out of the cloud, enter information about multiple mongos nodes to reduce the impact of the single-node failure on the synchronization task. In addition, multiple mongos nodes support load balancing. In addition, ensure that all mongos nodes belong to the same cluster instance.

  • During synchronization, do not modify or delete the usernames, passwords, permissions, or ports of the source and destination databases.

  • To ensure data consistency, do not modify the destination database (including but not limited to DDL and DML operations) during the entire synchronization process.

  • During the synchronization, data rollback caused by a primary/standby switchover of the source database is not supported.

  • The system database cannot be synchronized. The username and role must be manually created in the destination database.

  • Documents larger than 16 MB in the source database cannot be inserted or updated during incremental synchronization.

  • In the incremental synchronization phase, concurrent replay is performed at the collection level to maintain the synchronization performance. In the following scenarios, only single-thread write is supported and concurrent replay is not supported:

    • The collection index contains a unique key.

    • The value of capped of the collection attribute is true.

    In either of the preceding scenarios, the task delay may increase.

  • To prevent loopback, the to-the-cloud migration task and out-of-cloud synchronization task cannot be started at the same time.

  • During row comparison, if an orphan document exists in a cluster instance or chunks are being synchronized, the number of returned rows is incorrect and the comparison results are inconsistent.

Procedure

This section uses real-time incremental synchronization from DDS to MongoDB as an example to describe how to configure a real-time synchronization task.

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

  2. On the Create Synchronization Instance page, specify the task name, description, and the synchronization instance details, and click Next.

    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 !=<>'&"\

    Table 4 Synchronization instance settings

    Parameter

    Description

    Data Flow

    Select Out of the cloud.

    Source DB Engine

    Select DDS.

    Destination DB Engine

    Select MongoDB.

    Network Type

    The Public network is used as an example. Available options: VPC, Public network and VPN or Direct Connect

    Source DB Instance

    An available DDS 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

    • Incremental

      Through log parsing, incremental data generated on the source database is synchronized to the destination database.

      During synchronization, the source database continues to provide services for external systems with zero downtime.

    Specifications

    DRS instance specifications. Different specifications have different performance upper limits. For details, see Real-Time Synchronization.

    Tags

    • This setting is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 20 tags.

    • After a task is created, you can view its tag details on the Tags tab. For details, see Tag Management.

    Note

    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.

    Table 5 Source database settings

    Parameter

    Description

    DB Instance Name

    The DDS instance that you selected when creating the replication instance and cannot be changed.

    Database Username

    The username for accessing the source database.

    Database Password

    The password for the database username.

    Note

    The IP address, port, username, and password of the source database are encrypted and stored in the database and the synchronization instance, and will be cleared after the task is deleted.

    Table 6 Destination database settings

    Parameter

    Description

    IP Address or Domain Name

    IP address or domain name of the destination database in the IP address/Domain name:Port format. The port of the destination database. Range: 1 - 65535

    You can enter up to 3 groups of IP addresses or domain names of the source database. Separate multiple values with commas (,). For example: 192.168.0.1:8080,192.168.0.2:8080. Ensure that the entered IP addresses or domain names belong to the same instance.

    Note

    If multiple IP addresses or domain names are entered, the test connection is successful as long as one IP address or domain name is accessible. Therefore, you must ensure that the IP address or domain name is correct.

    Authentication Database

    The name of the destination database.

    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 the SSL certificate is not used, your data may be at risk.

    Note

    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 Task page, select the start point and synchronization objects, and click Next.

    Table 7 Synchronization Object

    Parameter

    Description

    Start Point

    The start time of incremental synchronization. The value is in the format of timestamp:incre. timestamp is the Unix timestamp (unit: second), and incre is the command execution sequence in a second. A synchronization task obtains incremental logs of the source database from the start position (including the current start position).

    • Run db.getSiblingDB("local").oplog.rs.find() to query the source database oplog. The format of the ts field is timestamp:incre.

    • A cluster cannot query the oplog from mongos. timestamp can be converted into the Unix timestamp format based on the start time. The value of incre is 1.

    Synchronization Object

    DRS supports database- and table-level synchronization. You can select data for synchronization based on your service requirements.

    Note

    • You can search for table names to quickly select the required database objects.

    • 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.

    • If all check items are successful, click Next.

      Note

      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 Confirm Task page, specify Start Time, confirm that the configured information is correct, and click Submit to submit the task.

    Table 8 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.

  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 image1 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 reconfigure the task, DRS applies for resources for the task again.

last updated: 2025-08-29 16:31 UTC - commit: 8af522c0c2f5c7b2f476683f03e2977dd6b4a90a