Data Transmission Service:Synchronize ApsaraDB for MongoDB to PolarDB for MySQL

Prerequisites

• If your source is an ApsaraDB for MongoDB sharded cluster, apply for an endpoint for each shard node and ensure that all nodes share the same account and password. For more information, see Apply for a shard endpoint.

• Create a target PolarDB for MySQL cluster with more storage space than the source ApsaraDB for MongoDB instance uses. For more information, see Custom Purchase and Purchase a subscription cluster.

  Note

  We recommend provisioning 10% more storage space than the source database uses.

• In the target PolarDB for MySQL cluster, create a database and a table with a primary key. For more information, see Database management.

  Important

  • Ensure that the data types in the target table are compatible with the source MongoDB data. For example, if the MongoDB _id field is an ObjectId, the corresponding column in the PolarDB for MySQL cluster must be varchar.

  • Do not name columns in the target PolarDB for MySQL table _id or _value.

Notes

Billing

Synchronization types

Database account permissions

Procedure

1. Go to the data synchronization task list page in the destination region. You can do this in one of two ways.

   DTS console

   1. Log on to the DTS console.

   2. In the navigation pane on the left, click Data Synchronization.

   3. In the upper-left corner of the page, select the region where the synchronization instance is located.

   DMS console

   Note

   The actual steps may vary depending on the mode and layout of the DMS console. For more information, see Simple mode console and Customize DMS console layout and style.

   1. Log on to the DMS console.

   2. In the top menu bar, choose Data + AI > DTS (DTS) > Data Synchronization.

   3. To the right of Data Synchronization Tasks, select the region of the synchronization instance.

2. Click Create Task to open the task configuration page.

3. Configure the source and destination databases.

   Category	Parameter	Description
   N/A	Task Name	DTS automatically generates a task name. We recommend that you specify a descriptive name for easy identification. The name does not need to be unique.
   Source Database	Select Existing Connection	Select the registered database instance with DTS from the drop-down list. The database information below is automatically configured. Note In the DMS console, this configuration item is Select a DMS database instance. If you have not registered the database instance or do not need to use a registered instance, manually configure the database information below.
   	Database Type	Select MongoDB.
   	Access Method	Select Alibaba Cloud Instance.
   	Instance Region	Select the region of the source ApsaraDB for MongoDB instance.
   	Replicate Data Across Alibaba Cloud Accounts	For this example, select No, as the database instance belongs to the current Alibaba Cloud account.
   	Architecture	In this example, select Replica Set. Note If your source ApsaraDB for MongoDB instance uses a Sharded Cluster architecture, you must also specify the Shard account and Shard password.
   	Migration Method	Select a method for incremental data synchronization based on your requirements. Oplog (Recommended): This option is available if Oplog is enabled for the source database. Note Oplog is enabled by default for self-managed MongoDB databases and ApsaraDB for MongoDB instances. This method offers lower latency for incremental synchronization tasks because logs are retrieved faster. We recommend selecting Oplog. ChangeStream: This option is available if Change Streams are enabled for the source database. Note If the source database is an Amazon DocumentDB (non-elastic cluster) instance, you can select only ChangeStream. If you set Architecture of the source database to Sharded Cluster, you do not need to specify Shard account and Shard password.
   	Instance ID	Select the ID of the source ApsaraDB for MongoDB instance.
   	Authentication Database	Enter the name of the database to which the database account belongs in the source ApsaraDB for MongoDB instance. If you have not modified it, the default value is admin.
   	Database Account	Enter the database account of the source ApsaraDB for MongoDB instance. For information about the required permissions, see database account permissions.
   	Database Password	Enter the password for the specified database account.
   	Encryption	DTS supports three connection methods: Non-encrypted, SSL-encrypted, and Mongo Atlas SSL. The options for Encryption vary based on the selected Access Method and Architecture. The options displayed in the console prevail. Note A MongoDB database where the Architecture is Sharded Cluster and the Migration Method is Oplog does not support SSL-encrypted. If the source is a self-managed MongoDB database (Access Method is not Alibaba Cloud Instance) with a Replica Set architecture, and you select SSL-encrypted, DTS also allows you to upload a CA certificate to verify the connection.
   Destination Database	Select Existing Connection	Select the registered database instance with DTS from the drop-down list. The database information below is automatically configured. Note In the DMS console, this configuration item is Select a DMS database instance. If you have not registered the database instance or do not need to use a registered instance, manually configure the database information below.
   	Database Type	Select PolarDB for MySQL.
   	Access Method	Select Alibaba Cloud Instance.
   	Instance Region	Select the region of the destination PolarDB for MySQL cluster.
   	Replicate Data Across Alibaba Cloud Accounts	For this example, select No, as the database instance belongs to the current Alibaba Cloud account.
   	PolarDB Cluster ID	Select the ID of the destination PolarDB for MySQL cluster.
   	Database Account	Enter the database account of the destination PolarDB for MySQL cluster. For information about the required permissions, see database account permissions.
   	Database Password	Enter the password for the specified database account.
   	Encryption	Select a connection method based on your business requirements. For more information about SSL encryption, see Configure SSL encryption.

4. After completing the configuration, click Test Connectivity and Proceed at the bottom of the page.

   Note

   • Ensure that you add the CIDR blocks of the DTS servers (either automatically or manually) to the security settings of both the source and destination databases to allow access. For more information, see Add the IP address whitelist of DTS servers.

   • If the source or destination is a self-managed database (i.e., the Access Method is not Alibaba Cloud Instance), you must also click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

5. Configure the task objects.

   1. On the Configure Objects page, specify the objects to synchronize.

      Parameter	Description
      Synchronization Types	By default, Incremental Data Synchronization is selected, which supports only Full Data Synchronization. Schema Synchronization is not supported. After the precheck is complete, DTS initializes the synchronization objects in the destination cluster with data from the source instance. This initial data serves as the baseline for subsequent incremental synchronization.
      Processing Mode of Conflicting Tables	Precheck and Report Errors: Checks for tables with the same names in the destination database. If any tables with the same names are found, an error is reported during the precheck and the data synchronization task does not start. Otherwise, the precheck is successful. Note If you cannot delete or rename the table with the same name in the destination database, you can map it to a different name in the destination. For more information, see Object name mapping. Ignore Errors and Proceed: Skips the check for tables with the same name in the destination database. Warning Selecting Ignore Errors and Proceed may cause data inconsistency and put your business at risk. For example: If the table schemas are consistent and a record in the destination database has the same primary key or unique key value as a record in the source database: During full data synchronization, DTS retains the destination record and skips the source record. During incremental synchronization, DTS overwrites the destination record with the source record. If the table schemas are inconsistent, data initialization may fail. This can result in only partial data synchronization or a complete synchronization failure. Use with caution.
      Capitalization of Object Names in Destination Instance	Configure the case-sensitivity policy for database, table, and column names in the destination instance. By default, the DTS default policy is selected. You can also choose to use the default policy of the source or destination database. For more information, see Case policy for destination object names.
      Source Objects	In the Source Objects box, click the objects, and then click to move them to the Selected Objects box. Note You can select objects to synchronize at the collection level.
      Selected Objects	Edit database name mapping. In the Selected Objects box, right-click the database that contains the collection to be synchronized. Change the Schema Name to the name of the database in the destination PolarDB for MySQL cluster that will receive the data. Click OK. Edit table name mapping. In the Selected Objects box, right-click the collection to be synchronized. Change the Table Name to the name of the table in the destination PolarDB for MySQL cluster that will receive the data. Optional: Set filter conditions for full data synchronization. For more information, see Set filter conditions. The syntax for filter conditions differs from standard SQL WHERE clauses and must use MongoDB query syntax. For example, to filter by user ID, enter {"_id": {$gt:"user100844658590795****",$lte:"user101674868045948****"}}, where $gt means "greater than" and $lte means "less than or equal to". Optional: In the Select DDL and DML Operations to Be Synchronized section, select the operations to synchronize incrementally. Available DDL operations include CREATE INDEX and DROP INDEX. Available DML operations include insert, update, and delete. You can click Select All to select all operations at once. Configure the MongoDB fields to be synchronized. By default, DTS maps the data of the collections to be synchronized and configures an expression in the Parameter Value column. You must verify that the expression meets your requirements and specify the Column Name, Type, Length, and Precision parameters. Important You must assign the value bson_value("_id") to the primary key column of the destination table. When you configure a bson_value() expression, you must specify the path down to the lowest-level subfield in the hierarchy. Otherwise, data loss may occur or the task may fail. In the Parameter Value column, view the MongoDB field name for the current row in the bson_value() expression. The field name is specified within double quotation marks (""). For example, if the expression is bson_value("age"), the row corresponds to the age field in MongoDB. Optional: Delete fields that you do not need to synchronize. Note To delete a field that you do not need to synchronize, click the icon in the corresponding row. Configure the fields to be synchronized. Proceed based on whether the bson_value() expression meets your requirements. Default expression Enter a Column Name. Note This is the name of the column in the table that receives data in the destination PolarDB for MySQL cluster. Select a data Type for the column. Important Ensure that the data type of the destination table is compatible with the data in the source MongoDB database. For more information about data type mappings, see Data type mapping. Optional: Configure the Length and Precision for the column data. Repeat the preceding steps to map all relevant fields. Custom expression Note This includes fields with hierarchical relationships, such as parent-child structures. In the Actions column, click the icon in the corresponding row. Click + Add Column. Configure the Column Name, Type, Length, and Precision. In the text box under Parameter Value, enter a bson_value() expression. For more information, see Value assignment examples. Repeat the preceding steps to map all relevant fields. Click OK.

   2. Click Next: Advanced Settings.

      Parameter	Description
      Dedicated Cluster for Task Scheduling	By default, DTS uses a shared cluster for tasks, so you do not need to make a selection. For greater task stability, you can purchase a dedicated cluster to run the DTS synchronization task. For more information, see What is a DTS dedicated cluster?.
      Select the engine type of the destination database	Select an engine type for the destination database based on your business requirements. InnoDB: The default storage engine. X-Engine: A database storage engine for online transaction processing (OLTP).
      Retry Time for Failed Connections	If the connection to the source or destination database fails after the synchronization task starts, DTS reports an error and immediately begins to retry the connection. The default retry duration is 720 minutes. You can customize the retry time to a value from 10 to 1,440 minutes. We recommend a duration of 30 minutes or more. If the connection is restored within this period, the task resumes automatically. Otherwise, the task fails. Note If multiple DTS instances (e.g., Instance A and B) share a source or destination, DTS uses the shortest configured retry duration (e.g., 30 minutes for A, 60 for B, so 30 minutes is used) for all instances. DTS charges for task runtime during connection retries. Set a custom duration based on your business needs, or release the DTS instance promptly after you release the source/destination instances.
      Retry Time for Other Issues	If a non-connection issue (e.g., a DDL or DML execution error) occurs, DTS reports an error and immediately retries the operation. The default retry duration is 10 minutes. You can also customize the retry time to a value from 1 to 1,440 minutes. We recommend a duration of 10 minutes or more. If the related operations succeed within the set retry time, the synchronization task automatically resumes. Otherwise, the task fails. Important The value of Retry Time for Other Issues must be less than that of Retry Time for Failed Connections.
      Enable Throttling for Full Data Synchronization	During full data synchronization, DTS consumes read and write resources from the source and destination databases, which can increase their load. To mitigate pressure on the destination database, you can limit the migration rate by setting Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s). Note This parameter is available only if Synchronization Types is set to Full Data Synchronization. You can also adjust the rate of full data synchronization when the synchronization instance is running.
      Only one data type for primary key _id in a table of the data to be synchronized	Specifies whether the primary key _id has a single, consistent data type within each collection to be synchronized. Important Select an option based on your actual data. An incorrect selection may lead to data loss. This parameter is available only if Synchronization Types includes Full Data Synchronization. Yes: The data types are unique. During the full synchronization phase, DTS does not scan the data types of the primary keys in the source data. For each collection, DTS synchronizes only the data corresponding to one primary key data type. No: The data types are not unique. During the full synchronization phase, DTS scans the data types of the primary keys in the source data and synchronizes all the data.
      Enable Throttling for Incremental Data Synchronization	You can also limit the incremental synchronization rate to reduce pressure on the destination database by setting RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s).
      Environment Tag	You can select an environment tag to identify the instance based on your business requirements. No tag is needed in this example.
      Configure ETL	Choose whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: Enables the ETL feature. Enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: Disables the ETL feature.
      Monitoring and Alerting	Choose whether to set up alerts. If the synchronization fails or the latency exceeds the specified threshold, DTS sends a notification to the alert contacts. No: No alerts are configured. Yes: Configures alerts. You must also set the alert threshold and alert notifications. For more information, see Configure monitoring and alerting during task configuration.

6. Save the task and perform a precheck.

   • To view the parameters for configuring this instance via an API operation, hover over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the tooltip.

   • If you have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.

   Note

   • Before a synchronization task starts, DTS performs a precheck. You can start the task only if the precheck passes.

   • If the precheck fails, click View Details next to the failed item, fix the issue as prompted, and then rerun the precheck.

   • If the precheck generates warnings:

     • For non-ignorable warning, click View Details next to the item, fix the issue as prompted, and run the precheck again.

     • For ignorable warnings, you can bypass them by clicking Confirm Alert Details, then Ignore, and then OK. Finally, click Precheck Again to skip the warning and run the precheck again. Ignoring precheck warnings may lead to data inconsistencies and other business risks. Proceed with caution.

7. Purchase the instance.

   1. When the Success Rate reaches 100%, click Next: Purchase Instance.

   2. On the Purchase page, select the billing method and link specifications for the data synchronization instance. For more information, see the following table.

      Category	Parameter	Description
      New Instance Class	Billing Method	Subscription: You pay upfront for a specific duration. This is cost-effective for long-term, continuous tasks. Pay-as-you-go: You are billed hourly for actual usage. This is ideal for short-term or test tasks, as you can release the instance at any time to save costs.
      	Resource Group Settings	The resource group to which the instance belongs. The default is default resource group. For more information, see What is Resource Management?.
      	Instance Class	DTS offers synchronization specifications at different performance levels that affect the synchronization rate. Select a specification based on your business requirements. For more information, see Data synchronization link specifications.
      	Subscription Duration	In subscription mode, select the duration and quantity of the instance. Monthly options range from 1 to 9 months. Yearly options include 1, 2, 3, or 5 years. Note This option appears only when the billing method is Subscription.

   3. Read and select the checkbox for Data Transmission Service (Pay-as-you-go) Service Terms.

   4. Click Buy and Start, and then click OK in the OK dialog box.

      You can monitor the task progress on the data synchronization page.

Data type mapping

Assignment configuration example

{
  "_id":"62cd344c85c1ea6a2a9f****",
  "person":{
    "name":"neo",
    "age":26,
    "sex":"male"
  }
}