Updated on 2024-03-28 GMT+08:00

From MongoDB to DDS

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB

  • On-premises MongoDB (versions 3.2, 3.4, 3.6, 4.0, 4.2, and 4.4)
  • ECS-hosted MongoDB (versions 3.2, 3.4, 3.6, 4.0, 4.2, and 4.4)
  • Other Cloud MongoDB 3.2, 3.4, 3.6, 4.0, 4.2, and 4.4
  • DDS DB instances (versions 3.2, 3.4, 4.0, 4.2, and 4.4)
  • DDS DB instances (versions 3.4, 4.0, 4.2, and 4.4)
    NOTE:

    The destination database version must be the same as or later than the source database version.

Database Account Permission Requirements

To start a migration task, the source and destination database users must have permissions listed in the following table. Different types of migration tasks require different permissions. For details, see Table 2. DRS automatically checks the database account permissions in the pre-check phase and provides handling suggestions.

Table 2 Database account permission

Type

Full Migration

Full+Incremental Migration

Source database user

  • Replica set: The source database user must have the readAnyDatabase permission for the admin database.
  • Single node: The source database user must have the readAnyDatabase permission for the admin database.
  • Cluster: The source database user must have the readAnyDatabase permission for the admin database and the read permission for the config database.
  • To migrate accounts and roles of the source database, the source and destination database users must have the read permission for the system.users and system.roles system tables of the admin database.
  • 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 mongos node user must have the readAnyDatabase permission for the admin database and the read permission for the config database. The source shard node user must have the readAnyDatabase permission for the admin database and the read permission for the local database.
  • To migrate accounts and roles of the source database, the source and destination database users must have the read permission for the system.users and system.roles system tables of the admin database.

Destination database user

The user who connects to the destination database must have the dbAdminAnyDatabase permission of the admin database and the readWrite permission of the destination database.

If the destination database is a cluster instance, the database user must have the clusterManager permission for the admin database.

  • 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.
  • For example, the source database user must have the readAnyDatabase permission for the admin database and the read permission for the config database.
    db.grantRolesToUser("Username",[{role:"readAnyDatabase",db:"admin"}, {role:"read",db:"config"}])

Supported Migration Objects

Different types of migration tasks support different migration objects. For details, see Table 3. DRS will automatically check the objects you selected before the migration.

Table 3 Migration objects

Type

Precautions

Migration objects

  • You can select table-, database-, or instance-level (all-level) migration.
  • Replica set: Only collections (including validator and capped collections), indexes, and views can be migrated.
  • Cluster: Only collections (including validator and capped collections), shard keys, indexes, and views can be migrated.
  • Single node: Only collections (including validator and capped collections), indexes, and views can be migrated.
  • Only user data and source database account information can be migrated. The system databases (for example, local, admin, and config) and system collection cannot be migrated. If service data is stored in the system database, run the renameCollection command to move the service data to the user database.
  • The statement for creating a view cannot contain a regular expression.
  • 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.
  • Do not store non-UTF-8 character strings in the String field of the source database collection. Otherwise, data will be inconsistent before and after the migration.
  • If the source is a cluster instance of version 4.4, composite hash indexes and composite hash shard keys are not supported.
  • If the source is a replica set instance of version 4.4, composite hash indexes are not supported.

Precautions

To ensure tasks can run normally, DRS provides automatic pre-check. Before starting a DRS task, DRS checks the configurations and conditions of the source and destination databases. For details about the main check items and handling suggestions, see DRS Pre-Check Items. In addition to the pre-check items, you need to pay attention to the items listed in Table 4.

Table 4 Precautions

Type

Restrictions

Restrictions on the source database

  • The source cannot be a GeminiDB Mongo instance.
  • The source database name cannot contain /\.$ or spaces. The collection name and view name cannot start with system. or contain the dollar sign ($).
  • When multiple source databases are migrated to the same destination database, the name of the database to be migrated must be unique.
  • Replica set: The MongoDB replica set instance must be available and have primary nodes.
  • If you need to perform an incremental migration for a single node instance, the source database must be a DDS single-node instance on the current cloud.

Use restrictions

General

  • During the migration, do not modify or delete the usernames, passwords, and permissions of the source and destination databases or change the ports of the source and destination databases.
  • During migration, do not modify the destination database (including but not limited to DDL and DML operations) that is being migrated.
  • During migration, data rollback caused by a primary/standby switchover of the source database is not supported.
  • During the migration, documents larger than 16 MB in the source database cannot be inserted or updated.
  • During the migration, do not run sh.moveChunk() on the source database. Otherwise, the migrated data will be inconsistent.

Full migration

  • During task startup and full migration, do not perform DDL operations on the source database. Otherwise, the task may be abnormal.

Incremental migration

  • During an incremental migration of collections, you are advised not to rename the collections.
  • To ensure the migration performance, concurrent replay is performed at the set level in the incremental task phase. 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.

Data comparison

  • You are advised to compare data during off-peak hours of the source database 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.
  • During row comparison, if an orphan document exists in a cluster instance or chunks are being migrated, the number of returned rows is incorrect and the comparison results are inconsistent. For details, see MongoDB official documents.

Troubleshooting

  • If any problem occurs during task creation, startup, full synchronization, incremental synchronization, or completion, rectify the fault by referring to Troubleshooting.

Other restrictions

  • If the source database is not on a cluster instance, the following operations and commands are supported during incremental migration:
    • 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.
  • During a full plus incremental migration between clusters, the objects to be migrated cannot be deleted. Otherwise, the migration task fails.
  • If you select Cluster (MongoDB 4.0+) for Source DB Instance Type, DRS will use the MongoDB change streams feature during the migration. Note the following before you use change streams:
    • Data subscription using change streams consumes a certain amount of CPU and memory resources of the source database. Evaluate the resources of the source database 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.
    • Change streams support only the following DDLs: drop database, drop collection and rename
    • The DBPointer and DBRef data types are not supported.
    • In the incremental migration phase,the migration speed can reach up to 10,000 rows in a single table per second.
    • Currently, only whitelisted users can use Change Streams.
  • If you select Oplog for Source Database Type, DRS will create multiple subtasks based on the number of source shards. If Task Rate Limit is selected, the configured rate limit value is synchronized to each subtask.
  • If a Time-to-Live (TTL) index already exists in the collection of the source database or is created during an incremental migration, 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 destination database version is DDS 4.2, DRS does not migrate compression parameters because the destination database does not support compression parameter settings.
  • If the accounts and roles to be migrated conflict with those in the destination database, DRS will skip the conflict data and continue the migration.
  • If the MongoDB service of the source database is deployed with other services on the same server, set the value of the cacheSizeGB parameter to the half of the minimum idle cache for the WiredTiger engine of the source database.
  • If the source is a replica set instance, enter information about all primary and secondary nodes to reduce the impact of a primary/secondary switchover on the migration task. If you enter information about multiple primary and secondary nodes, ensure that all nodes belong to the same replica set instance.
  • If the source is a cluster instance, enter information about multiple mongos nodes to reduce the impact of single-node failure on the migration task. In addition, ensure that all mongos nodes belong to the same cluster instance. For an incremental migration of a cluster instance, you are advised to enter information about all primary and secondary nodes of the shard node and ensure that all node information belongs to the same shard to reduce the impact of a primary/secondary switchover on the migration task. Ensure that all shard nodes belong to the same cluster.
  • During the creation of a migration task, the destination database can be set to read-only or read/write if the DDS kernel version supports this setting. After the task is created, this setting cannot be changed.
    • Read-only: During the migration, the destination database is read-only. After the migration is complete, it restores to the read/write status. This option ensures the integrity and success rate of data migration.
    • Read/Write: During the migration, the destination database can be queried or modified. Data being migrated may be modified when operations are performed or applications are connected. It should be noted that background processes can often generate or modify data, which may result in data conflicts, task faults, and upload failures. Do not select this option if you do not fully understand the risks.
  • In some migration scenarios, to prevent the drop database operation from deleting the existing collections in the destination database, the drop database operation will not be synchronized to the destination database.
    • If the source database version is earlier than MongoDB 3.6, running the drop database command will delete the collections only from the source database. The collections in destination database will not be deleted.
    • If the source database version is MongoDB 3.6 or later, the drop database operation is represented by the drop database and drop collection operations in oplog. Running the drop database command will delete the collections from both the source and destination databases.
  • To accelerate the migration, delete unnecessary indexes from the source database and retain only necessary indexes before the migration. You are advised not to create indexes for the source database during the migration. If indexes must be created, create them in the background.
  • To prevent loopback, do not start tasks that migrate the same database to and out of the cloud at the same time.

Prerequisites

Procedure

This section uses a MongoDB sharded cluster as an example to describe how to configure a task for migrating data from MongoDB to DDS Community Edition over a public network.

  1. On the Online Migration Management page, click Create Migration Task.
  2. On the Create Replication Instance page, select a region and project, specify the task name, description, and the replication instance details, and click Create Now.

    • Task information description
      Figure 1 Migration task information
      Table 5 Task information

      Parameter

      Description

      Region

      The region where the replication instance is deployed. You can change the region. To reduce latency and improve access speed, select the region closest to your services.

      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 !=<>'&"\

    • Replication instance information
      Figure 2 Replication instance information

      Table 6 Replication instance settings

      Parameter

      Description

      Data Flow

      Select To the cloud.

      The destination database must be a database on the current cloud.

      Source DB Engine

      Select MongoDB.

      Destination DB Engine

      Select DDS.

      Network Type

      Available options: VPC, VPN or Direct Connect, and Public network. By default, the value is Public network.

      • VPC is suitable for migrations between cloud databases of the same account in the same region.
      • Public network is suitable for migrations from on-premises or external cloud databases to the destination databases bound with an EIP.
      • VPN or Direct Connect is suitable for migrations from on-premises databases to cloud databases or between cloud databases across regions.

      Destination DB Instance

      Select the DB instance you have created.

      Replication Instance Subnet

      The subnet where the replication instance resides. 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 there are available IP addresses for the subnet. To ensure that the replication instance is successfully created, only subnets with DHCP enabled are displayed.

      Migration Type

      • Full: This migration type is suitable for scenarios where service interruption is permitted. It migrates all objects and data in non-system databases to the destination database at one time. The objects include collections, views, and indexes.
        NOTE:

        If you are performing a full migration, do not perform operations on the source database. Otherwise, data generated in the source database during the migration will not be synchronized to the destination database.

      • Full+Incremental: This migration type allows you to migrate data without interrupting services. After a full migration initializes the destination database, an incremental migration initiates and parses logs to ensure data consistency between the source and destination databases.
        NOTE:

        If you select Full+Incremental, data generated during the full migration will be continuously synchronized to the destination database, and the source remains accessible.

      Source DB Instance Type

      If you select Full+Incremental for Migration Type, set this parameter based on the source database.

      • If the source database is a cluster instance, set this parameter to Cluster.
      • If the source database is a replica set or a single node instance, set this parameter to Non-cluster.

      Obtain Incremental Data

      If Source DB Instance Type is set to Cluster and Migration Mode is set to Full+Incremental, you need to determine how to capture data changes during the incremental synchronization. Also, the balancer of the source database must be disabled and orphaned documents must be deleted. For details, see How Do I Disable the Balancer? and How Do I Delete Orphaned Documents in MongoDB Sharded Clusters?

      • oplog: For MongoDB 3.2 or later, DRS directly connects to each shard of the source DB instance to extract data. If you select this method, you need to enter the connection information of each shard in the source database when testing the connection between the source database and the DRS instance.
      • changeStream: This method is recommended. For MongoDB 4.0 and later, DRS connects to mongos nodes of the source database to extract data. If you select this method, you must enable the WiredTiger storage engine of the source database.
      NOTE:

      Only whitelisted users can use changeStream. To use this function, submit a service ticket. In the upper right corner of the management console, choose Service Tickets > Create Service Ticket to submit a service ticket.

      Destination Database Access

      During the migration, the destination DDS instance can be set to read-only or read/write. This setting is available only for DDS 4.0 and cannot be changed after a migration task is created.

      • Read-only

        During migration, the destination database is read-only. After the migration is complete, it restores to the read/write status. This option ensures the integrity and success rate of data migration.

      • Read/Write

        During the migration, the destination database can be queried or modified. Data being migrated may be modified when operations are performed or applications are connected. It should be noted that background processes can often generate or modify data, which may result in data conflicts, task faults, and upload failures. Do not select this option if you do not fully understand the risks. Set the destination database to Read/Write only when you need to modify other data in the database during the migration.

        The task cannot be modified after being created.

      NOTE:

      Only whitelisted users can use Destination Database Access. To use this function, submit a service ticket. In the upper right corner of the management console, choose Service Tickets > Create Service Ticket to submit a service ticket.

      Source Shard Quantity

      If Source DB Instance Type is set to Cluster and Obtain Incremental Data is set to oplog, you need to enter the number of source database shards.

      The number of source shards ranges from 2 to 32. Specify this parameter based on the actual number of shards in the source DB.

    • AZ
      Figure 3 AZ
      Table 7 Task AZ

      Parameter

      Description

      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 8 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 projects, 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 replication 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 replication instance. After the connection tests are successful, select the check box before the agreement and click Next.

    • Source database information
      Figure 5 Source database information
      Table 9 Source database information

      Parameter

      Description

      mongos Address

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

      You can enter a maximum of three 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 sharded cluster.

      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 authentication database. For example: The default authentication database of DDS instance is admin.

      mongos Username

      The username for accessing the source database.

      mongos 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 disabled, your data may be at risk.

      Sharded Database

      Enter the information about the sharded databases in the source database. If the source is a DDS instance, apply for an IP address for the shard node by referring to Document Database Service User Guide.

      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.

    • Destination database configuration
      Figure 6 Destination database information
      Table 10 Destination database settings

      Parameter

      Description

      DB Instance Name

      The DB instance you selected when creating the migration task. This parameter cannot be changed.

      Authentication Database

      The name of the authentication database. For example: The default authentication database of DDS instance is admin.

      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 disabled, your data may be at risk.

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

  4. On the Set Task page, select migration objects and click Next.

    Figure 7 Migration object
    Table 11 Migrate Object

    Parameter

    Description

    Flow Control

    You can choose whether to control the flow. Flow Control takes effect in the full phase only.

    • 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 migration speed is not limited and the outbound bandwidth of the source database is maximally used, which causes read consumption on the source database accordingly. 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:
      • Flow control mode takes effect only during a full migration.
      • If you select Cluster for Source DB Instance Type and oplog for Obtain Incremental Data in 2, the flow control settings will be synchronized to each subtask.
      • You can also change the flow control mode after creating a task. For details, see Modifying the Flow Control Mode.

    Migrate Account

    Accounts to be migrated can be classified into the following types: accounts that can be migrated and accounts that cannot be migrated. You can choose whether to migrate the accounts. Accounts that cannot be migrated or accounts that are not selected will not exist in the destination database. Ensure that your services will not be affected by these accounts.
    • No

      During the migration, accounts and roles are not migrated.

    Migrate Object

    The left pane displays the source database objects, and the right pane displays the selected objects. You can choose to migrate all objects, tables, or databases based on your service requirements.

    • All: All objects in the source database are migrated to the destination database. After the migration, the object names will remain the same as those in the source database and cannot be modified.
    • Tables: The selected table-level objects will be migrated.
    • Databases: The selected database-level objects will be migrated.

    If the source database is changed, click in the upper right corner before selecting migration objects to ensure that the objects to be selected are from the changed source database.

    NOTE:
    • If you choose not to migrate all of the databases, the migration may fail because the objects, such as stored procedures and views, in the databases to be migrated may have dependencies on other objects that are not migrated. To prevent migration failure, migrate all of the databases.
    • 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 migration object cannot contain spaces.
    • To quickly select the desired database objects, you can use the search function.

  5. On the Check Task page, check the migration 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.

      Figure 9 Pre-check
    • If the check is complete and the check success rate is 100%, click Next.

      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 and confirm that the configured information is correct and click Submit to submit the task.

    Figure 10 Task startup settings
    Table 12 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. The Start at a specified time option is recommended.

    NOTE:

    The migration task may affect the performance of the source and destination databases. You are advised to start the task in off-peak hours and reserve two to three days for data verification.

    Send Notifications

    This parameter is optional. After enabled, select a SMN topic. If the status, latency metric, or data of the migration 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 migration, 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:
    • In the early stages of an incremental migration, there is more delay because more data is waiting to be synchronized. In this situation, no notifications will be sent.
    • Before setting the delay threshold, enable Send Notifications.
    • If the delay threshold is set to 0, no notifications will be sent to the recipient.

    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:

    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, view and manage it on the Online Migration 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 reconfigure the task, DRS applies for resources again.