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Data Transmission Service:Synchronize data from an ApsaraDB for MongoDB instance (replica set architecture) to another ApsaraDB for MongoDB instance (replica set architecture or sharded cluster architecture)

Last Updated:Dec 21, 2023

You can use Data Transmission Service (DTS) to synchronize data from a MongoDB database(replica set architecture) to another MongoDB database(replica set architecture or sharded cluster architecture).

Supported source and destination databases

The following table lists the types of source and destination MongoDB databases that are supported by DTS. In this example, the source database is an ApsaraDB for MongoDB instance (replica set architecture) and the destination database is an ApsaraDB for MongoDB instance (replica set architecture or sharded cluster architecture). You can also follow the procedure to configure data synchronization tasks for other types of MongoDB databases.

Source database

Destination database

ApsaraDB for MongoDB instance (replica set architecture)

ApsaraDB for MongoDB instance (replica set architecture or sharded cluster architecture)

Self-managed MongoDB database (replica set architecture) that is hosted on an Elastic Compute Service (ECS) instance

Self-managed MongoDB database (replica set architecture or sharded cluster architecture) that is hosted on an ECS instance

Self-managed MongoDB database (replica set architecture) that is connected over Express Connect, VPN Gateway, or Smart Access Gateway

Self-managed MongoDB database (replica set architecture or sharded cluster architecture) that is connected over Express Connect, VPN Gateway, or Smart Access Gateway

Prerequisites

  • The source ApsaraDB for MongoDB instance (replica set architecture) and the destination ApsaraDB for MongoDB instance (replica set architecture or sharded cluster architecture) are created. For more information, see Create a replica set instance and Create a sharded cluster instance.

    Note

    For more information about the supported database versions, see Overview of data synchronization scenarios.

  • The available storage space of the destination ApsaraDB for MongoDB instance is 10% larger than the total size of the data in the source ApsaraDB for MongoDB instance.

  • Databases and collections to be sharded are created in the destination ApsaraDB for MongoDB instance and sharding is configured based on your business requirements if the destination ApsaraDB for MongoDB instance is deployed in the sharded cluster architecture. For more information, see Configure sharding to maximize the performance of shards.

    Note

    After you configure sharding for a sharded cluster instance, the synchronized data will be distributed among different shards. This maximizes the performance of the sharded cluster.

Limits

CategoryDescription
Limits on the source database
  • Bandwidth requirements: The server to which the source database is deployed must have a sufficient outbound bandwidth. Otherwise, the data synchronization speed is affected.
  • The collections to be synchronized must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records.
  • If you select collections as the objects to be synchronized and you want to edit collections, such as renaming collections, up to 1,000 collections can be synchronized in a single data synchronization task. If you run a task to synchronize more than 1,000 collections, a request error occurs. In this case, we recommend that you configure multiple tasks to synchronize the collections in batches or configure a task to synchronize the entire database.
  • The oplog feature must be enabled.
    Note

    For an incremental data synchronization task, the oplogs of the source database must be stored for more than 24 hours. If you perform both full data synchronization and incremental data synchronization, the oplogs of the source database must be stored for at least seven days. Otherwise, DTS may fail to obtain the oplogs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. After the full data synchronization is complete, you can set the retention period to more than 24 hours. Make sure that you set the retention period of oplogs in accordance with the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not guarantee service reliability or performance.

Other limits
  • To ensure compatibility, the version of the destination MongoDB database must be the same as or later than the version of the source MongoDB database. If the version of the destination database is earlier than that of the source database, database compatibility issues may occur.
  • DTS cannot synchronize data from the admin or local database.
  • Transaction information is not retained. When transactions are synchronized to the destination database, transactions are converted into a single record.
  • Before you synchronize data, evaluate the impact of data synchronization on the performance of the source and destination databases. We recommend that you synchronize data during off-peak hours. During full data synchronization, DTS uses read and write resources of the source and destination databases. This may increase the loads on the database servers.
  • During full data synchronization, concurrent INSERT operations cause fragmentation in the collections of the destination database. After full data synchronization is complete, the storage usage of collections in the destination database is larger than that of collections in the source database.
  • During data synchronization, we recommend that you use only DTS to write data to the destination database. This prevents data inconsistency between the source and destination databases. If you use tools other than DTS to write data to the destination database, data loss may occur in the destination database when you use Data Management (DMS) to perform online DDL operations.
  • The data is concurrently written to the destination database. Therefore, the storage space occupied in the destination database is 5% to 10% larger than the size of the data in the source database.
  • You must use the db.$table_name.aggregate([{ $count:"myCount"}]) syntax to query the return value of a count operation on the destination MongoDB database.
  • Make sure that the destination MongoDB database does not have the same primary key as the source database. The default primary key is _id. Otherwise, data loss may occur in the destination database. If the destination database has the same primary key as the source database, clear the related data in the destination database without interrupting the services of DTS. If the same primary key is _id, you can delete the data in the destination database that has the same _id as the source database.
Special casesIf the source database is a self-managed MongoDB database, take note of the following limits:
  • If you perform a primary/secondary switchover on the source database when the data synchronization task is running, the task fails.
  • DTS calculates synchronization latency based on the timestamp of the latest synchronized data in the destination database and the current timestamp in the source database. If no update operation is performed on the source database for a long time, the synchronization latency may be inaccurate. If the latency of the synchronization task is too high, you can perform an update operation on the source database to update the latency.
Note If you select an entire database as the object to be synchronized, you can create a heartbeat. The heartbeat is updated or receives data every second.

Billing

Synchronization typeTask configuration fee
Schema synchronization and full data synchronizationFree of charge.
Incremental data synchronizationCharged. For more information, see Billing overview.

Supported synchronization topologies

  • One-way one-to-one synchronization

  • One-way one-to-many synchronization

  • One-way many-to-one synchronization

  • One-way cascade synchronization

For more information about the synchronization topologies that are supported by DTS, see Synchronization topologies.

Synchronization types

Synchronization type

Description

Schema synchronization

DTS synchronizes the schemas of objects from the source ApsaraDB for MongoDB instance to the destination ApsaraDB for MongoDB instance.

Full data synchronization

DTS synchronizes all existing data of objects from the source ApsaraDB for MongoDB instance to the destination ApsaraDB for MongoDB instance.

Note

DTS supports full data synchronization for the following types of objects: database and collection.

Incremental data synchronization

DTS synchronizes incremental data from the source ApsaraDB for MongoDB instance to the destination ApsaraDB for MongoDB instance.

Note

DTS does not support incremental data synchronization from databases that are created after the task starts to run. DTS synchronizes incremental data generated by the following operations:

  • CREATE COLLECTION and CREATE INDEX

  • DROP DATABASE, DROP COLLECTION, and DROP INDEX

  • RENAME COLLECTION

Procedure

  1. Go to the Data Synchronization Tasks page.
    1. Log on to the Data Management (DMS) console.
    2. In the top navigation bar, click DTS.
    3. In the left-side navigation pane, choose DTS (DTS) > Data Synchronization.
    Note
  2. From the drop-down list to the right of Data Synchronization Tasks, select the region in which the data synchronization instance resides.
    Note If you use the new DTS console, you must select the region in which the data synchronization instance resides in the top navigation bar.
  3. Click Create Task. On the page that appears, configure the source and destination databases.

    Warning

    After you configure the source and destination databases, we recommend that you read the limits that are displayed in the upper part of the page. Otherwise, the task may fail or data inconsistency may occur.

    Section

    Parameter

    Description

    N/A

    Task Name

    The name of the task. DTS automatically assigns a name to the task. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to specify a unique task name.

    Source Database

    Select an existing DMS database instance

    The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements.

    • If you select an existing instance, DTS automatically populates the parameters for the database.

    • If you do not select an existing instance, you must manually configure parameters for the database.

    Database Type

    The type of the source database. Select MongoDB.

    Access Method

    The access method of the source database. Select Alibaba Cloud Instance.

    Instance Region

    The region in which the source ApsaraDB for MongoDB instance resides.

    Architecture

    The architecture in which the source instance is deployed. Select Replica Set.

    Instance ID

    The ID of the source ApsaraDB for MongoDB instance.

    Authentication Database

    The name of the authentication database to which the objects to be synchronized in the source ApsaraDB for MongoDB instance belong. If you did not change the name before, the default value is admin.

    Database Account

    The database account of the source ApsaraDB for MongoDB instance. The account must have read permissions on the source, admin, and local databases.

    Database Password

    The password of the database account.

    Destination Database

    Select an existing DMS database instance

    The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements.

    • If you select an existing instance, DTS automatically populates the parameters for the database.

    • If you do not select an existing instance, you must manually configure parameters for the database.

    Database Type

    The type of the destination database. Select MongoDB.

    Access Method

    The access method of the destination database. Select Alibaba Cloud Instance.

    Instance Region

    The region in which the destination ApsaraDB for MongoDB instance resides.

    Architecture

    The architecture in which the destination ApsaraDB for MongoDB instance is deployed.

    Instance ID

    The ID of the destination ApsaraDB for MongoDB instance.

    Authentication Database

    The name of the authentication database to which the synchronized objects in the destination ApsaraDB for MongoDB instance belong. If you did not change the name before, the default value is admin.

    Database Account

    The database account of the destination ApsaraDB for MongoDB instance. The account must have the dbAdminAnyDatabase permission, read and write permissions on the destination database, and read permissions on the local database.

    Database Password

    The password of the database account.

  4. In the lower part of the page, click Test Connectivity and Proceed.

    If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance, and you must ensure that the ECS instance can access the database. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the whitelist of the database to allow DTS to access the database. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.

    Warning

    If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database or instance, or to the ECS security group rules, security risks may arise. Therefore, before you use DTS to synchronize data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

  5. Configure objects to synchronize and advanced settings.

    Parameter

    Description

    Synchronization Type

    By default, Incremental Data Synchronization is selected. You must also select Schema Synchronization and Full Data Synchronization. After the precheck is complete, DTS synchronizes the historical data of selected objects from the source instance to the destination instance. The historical data is the basis for subsequent incremental synchronization.

    Note

    For more information, see Synchronization types.

    Processing Mode of Conflicting Tables

    • Precheck and Report Errors: checks whether the destination database contains collections that have the same names as collections in the source database. If the source and destination databases do not contain collections that have identical collection names, the precheck is passed. Otherwise, an error is returned during the precheck and the data synchronization task cannot be started.
      Note You can use the object name mapping feature to rename the collections that are synchronized to the destination database. You can use this feature if the source and destination databases contain collections that have identical names and the collections in the destination database cannot be deleted or renamed. For more information, see Rename an object to be synchronized.
    • Ignore Errors and Proceed: skips the precheck for identical collection names in the source and destination databases.
      Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to potential risks.
      • DTS does not synchronize data records that have the same primary key values as data records in the destination database.
      • Data may fail to be initialized, only some columns are synchronized, or the data synchronization task fails.

    Synchronization Topology

    Select One-way Synchronization.

    Capitalization of Object Names in Destination Instance

    The capitalization of database names and collection names in the destination instance. By default, DTS default policy is selected. You can select other options to ensure that the capitalization of object names is consistent with the default capitalization of object names in the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.

    Source Objects

    Select one or more objects from the Source Objects section and click the Rightwards arrow icon to add the objects to the Selected Objects section.

    Note

    You can select databases or collections as the objects to be synchronized.

    Selected Objects

    • To rename an object that you want to synchronize to the destination instance, right-click the object in the Selected Objects section. For more information, see Map the name of a single object.

    • To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time.

    Note
    • To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to synchronize. For more information about the SQL operations that can be synchronized, see Synchronization types.

    • To specify WHERE conditions to filter data, right-click an object in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Use SQL conditions to filter data.

  6. Click Next: Advanced Settings to configure advanced settings.

    • Data Verification Settings

      For more information about how to enable data verification, see Enable data verification.

    • Advanced Settings

      Parameter

      Description

      Set Alerts

      Specifies whether to configure alerting for the data migration task. If the task fails or the migration latency exceeds the specified threshold, the alert contacts will receive notifications. Valid values:

      • No: does not configure alerting.

      • Yes: configures alerting. If you select Yes, you must also specify the alert threshold and alert contacts. For more information, see Configure monitoring and alerting.

      Retry Time for Failed Connections

      The retry time range for failed connections. If the source or destination database fails to be connected after the data migration task is started, DTS immediately retries a connection within the retry time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS is reconnected to the source and destination databases within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails.

      Note
      • If you specify different retry time ranges for multiple data migration tasks that share the same source or destination database, the value that is specified later takes precedence.

      • When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.

      Configure ETL

      Specifies whether to configure the extract, transform, and load (ETL) feature. For more information, see What is ETL?. Valid values:
  7. Click Next: Save Task Settings and Precheck in the lower part of the page.

    You can move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters to view the parameter settings of the API operation that is called to configure the instance.

    Note
    • Before you can start the data synchronization task, DTS performs a precheck. You can start the data synchronization task only after the task passes the precheck.

    • If the task fails to pass the precheck, click View Details next to each failed item. After you troubleshoot the issues based on the causes, run a precheck again.

    • If an alert is triggered for an item during the precheck:

      • If an alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issues. Then, run a precheck again.

      • If an alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur, and your business may be exposed to potential risks.

  8. Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.

  9. On the Purchase Instance page, configure the Billing Method and Instance Class parameters for the data synchronization instance. The following table describes the parameters.

    Section

    Parameter

    Description

    New Instance Class

    Billing Method

    • Subscription: You pay for the instance when you create an instance. The subscription billing method is more cost-effective than the pay-as-you-go billing method for long-term use.

    • Pay-as-you-go: A pay-as-you-go instance is charged on an hourly basis. The pay-as-you-go billing method is suitable for short-term use. If you no longer require a pay-as-you-go instance, you can release the pay-as-you-go instance to reduce costs.

    Resource Group

    The resource group on which the instance is run. Default value: default resource group. For more information, see What is Resource Management?.

    Instance Class

    DTS provides various synchronization specifications that provide different performance. The synchronization speed varies based on the synchronization specifications that you select. You can select a synchronization specification based on your business scenario. For more information, see Specifications of data synchronization instances.

    Subscription Duration

    If you select the subscription billing method, set the subscription duration and the number of instances that you want to create. The subscription duration can be one to nine months, one year, two years, three years, or five years.

    Note

    This parameter is available only if you select the Subscription billing method.

  10. Read and select the check box to agree to the Data Transmission Service (Pay-as-you-go) Service Terms.

  11. Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.