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

Prerequisites

• If the source database is an ApsaraDB for MongoDB sharded cluster, apply for an endpoint for each shard node. Ensure that all shard nodes use the same account and password. For instructions, see Apply for a shard endpoint.

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

  Note

  We recommend that the target cluster has at least 10% more storage space than the used storage space of the source database.

• In the target PolarDB for MySQL cluster, create a database and a table to receive the data. The table must have a primary key. For more information, see Database management.

  Important

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

  • In the PolarDB for MySQL cluster, column names in the target table cannot be _id or _value.

Notes

Billing

Migration types

Required permissions for database accounts

Procedure

1. Navigate to the migration task list page for the destination region using one of the following methods.

   From the DTS console

   1. Log on to the Data Transmission Service (DTS) console.

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

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

   From the DMS console

   Note

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

   1. Log on to the Data Management (DMS) console.

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

   3. To the right of Data Migration Tasks, select the region where the migration instance is located.

2. Click Create Task to navigate to 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	To use a database instance that has been added to the system (created or saved), select the desired database instance from the drop-down list. The database information below will be automatically configured. Note In the DMS console, this parameter is named Select a DMS database instance.. If you have not registered the database instance with the system, 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 where the source ApsaraDB for MongoDB instance resides.
   	Replicate Data Across Alibaba Cloud Accounts	In this example, a database instance under the current Alibaba Cloud account is used. Select No.
   	Architecture	In this example, select Replica Set. Note If your source ApsaraDB for MongoDB instance is a Sharded Cluster, you must also specify the Shard account and Shard password.
   	Migration Method	Select a method for incremental data migration based on your requirements. Oplog (Recommended): This option is available if an oplog is enabled for the source database. Note An oplog is enabled by default for both self-managed MongoDB databases and ApsaraDB for MongoDB instances. This method offers lower latency for incremental data migration due to faster log pulling. Therefore, 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 instance (non-elastic cluster), you can only select ChangeStream. If you set Architecture to Sharded Cluster for the source database, you do not need to enter a Shard account or Shard password.
   	Instance ID	Select the ID of the source ApsaraDB for MongoDB instance.
   	Authentication Database	Enter the name of the database that the database account belongs to in the source ApsaraDB for MongoDB instance. If you have not changed it, the default value is admin.
   	Database Account	Enter the database account for the source ApsaraDB for MongoDB instance. For more 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	To use a database instance that has been added to the system (created or saved), select the desired database instance from the drop-down list. The database information below will be automatically configured. Note In the DMS console, this parameter is named Select a DMS database instance.. If you have not registered the database instance with the system, 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 where the destination PolarDB for MySQL cluster resides.
   	Replicate Data Across Alibaba Cloud Accounts	In this example, a database instance under the current Alibaba Cloud account is used. Select No.
   	PolarDB Cluster ID	Select the ID of the destination PolarDB for MySQL cluster.
   	Database Account	Enter the database account for the destination PolarDB for MySQL cluster. For more information about the required permissions, see Database account permissions.
   	Database Password	Enter the password for the database account.
   	Encryption	Select an option based on your business requirements. For more information about the SSL encryption feature, see Enable SSL encryption.

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

   Note

   • Ensure that the IP address segment of the DTS service is automatically or manually added to the security settings of the source and destination databases to allow access from DTS servers. For more information, see Add DTS server IP addresses to a whitelist.

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

5. Configure the task objects.

   1. On the Configure Objects page, configure the objects that you want to migrate.

      Parameter	Description
      Migration Types	If you only need to perform a full migration, select Full Data Migration. To perform a migration with no downtime, select both Full Data Migration and Incremental Data Migration. Note If you do not select Incremental Data Migration, do not write new data to the source instance during data migration to ensure data consistency.
      Processing Mode of Conflicting Tables	Precheck and Report Errors: Checks whether collections with the same names exist in the destination database. If no collections with the same names exist, the precheck is passed. If collections with the same names exist, an error is reported during the precheck, and the data migration task does not start. Note If a collection in the destination database has the same name but cannot be easily deleted or renamed, you can change the name of the collection in the destination database. For more information, see Object name mapping. Ignore Errors and Proceed: Skips the check for collections with the same names. Warning Selecting Ignore Errors and Proceed may cause data inconsistency and business risks. For example: If a record in the destination database has the same primary key value as a record in the source database, the record in the destination database is kept. The record from the source database is not migrated to the destination database. Data initialization may fail, only some data may be migrated, or the migration may fail.
      Capitalization of Object Names in Destination Instance	You can configure the case sensitivity policy for the names of migrated objects, such as databases, tables, and columns, in the destination instance. By default, DTS default policy is selected. You can also choose to keep the case sensitivity consistent with the default policy of the source or destination database. For more information, see Case sensitivity of object names in the destination database.
      Source Objects	In the Source Objects box, click the objects to migrate, and then click to move them to the Selected Objects box. Note You can select objects at the collection level.
      Selected Objects	Edit database name mapping. In the Selected Objects box, right-click the source database that contains the collections to migrate. In this example, the database name is dtsdb, which is at the root of the tree structure. Change the Schema Name to the name of the database that receives data in the destination PolarDB for MySQL cluster. In the Edit Schema panel, change the Schema Name to the destination name (for example, dtsdb). Click OK. Edit table name mapping. In the Selected Objects box, right-click the collection you want to migrate. For example, if the tree structure in the Selected Objects panel is dtsdb > Table > class, right-click the target collection. Change the Table Name to the name of the table that receives data in the destination PolarDB for MySQL cluster. After you right-click, you can modify the Table Name in the Edit Table page that appears (for example, class). Note: After you edit the table name or column names, the table name and column names in the destination database are changed to the new names. Optional: Set filter conditions for the full data migration. For more information, see Set filter conditions. In the Filter Conditions text box, you can enter a filter statement. The syntax is different from a standard SQL WHERE clause. For example, to filter by user ID, you can use: {"_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 for incremental data migration. In the Select DML Operations to Synchronize section, you can select insert, update, and delete. Configure the fields to migrate from MongoDB. By default, DTS maps the data of the collections to be migrated and configures expressions in the Parameter Value column. Check if the expressions meet your requirements and configure parameters such as Column Name, Type, Length, and Precision. Important You must assign the value bson_value("_id") to the primary key column of the destination table. When configuring a bson_value() expression, you must specify the path down to the lowest-level subfield in the hierarchy. Otherwise, data loss or task failure may occur. In the bson_value() expression of the Parameter Value column, check the name of the corresponding field in MongoDB. The text within the quotation marks ("") is the field name in MongoDB. For example, if the expression is bson_value("age"), this row corresponds to the age field in MongoDB. Optional: Delete fields that you do not need to migrate. Note To delete a field, click the icon in that row. Configure the fields to migrate. The next steps depend on whether the default bson_value() expression meets your requirements. Custom expressions Note This may apply to fields with a hierarchical structure, such as a parent-child relationship. In the Actions column, click the icon in the row. Click + Add Column. Configure the Column Name, Type, Length, and Precision. Important Ensure that the data types of the destination table are compatible with the source MongoDB data. For more information about data type mappings, see Data type mapping. In the text box under Parameter Value, enter the bson_value() expression. For more information, see Assignment configuration examples. Repeat these steps to map all relevant fields. Default expressions Enter the Column Name. Note This is the name of the column in the table that receives data in the destination PolarDB for MySQL cluster. Select the data Type for the column. Important Ensure that the data types of the destination table are compatible with the source MongoDB data. For more information about data type mappings, see Data type mapping. Optional: Configure the Length and Precision for the column data. Repeat these steps to map all relevant fields. Click OK.

   2. Click Next: Advanced Settings to configure advanced parameters.

      Parameter	Description
      Dedicated Cluster for Task Scheduling	By default, DTS schedules tasks on a shared cluster. You do not need to select one. If you want more stable tasks, you can purchase a dedicated cluster to run DTS migration tasks.
      Select the engine type of the destination database	Select the storage engine for the destination database based on your requirements. InnoDB: The default storage engine. X-Engine: An online transaction processing (OLTP) database storage engine.
      Retry Time for Failed Connections	After the migration task starts, if the connection to the source or destination database fails, 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 1440 minutes. We recommend that you set the duration to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified duration, the migration task automatically resumes. Otherwise, the task fails. Note For multiple DTS instances that share the same source or destination, the network retry time is determined by the setting of the last created task. Because you are charged for the task during the connection retry period, we recommend that you customize the retry time based on your business needs, or release the DTS instance as soon as possible after the source and destination database instances are released.
      Retry Time for Other Issues	After the migration task starts, if a non-connectivity issue, such as a DDL or DML execution exception, occurs in the source or destination database, DTS reports an error and immediately begins to retry the operation. The default retry duration is 10 minutes. You can customize the retry time to a value from 1 to 1440 minutes. We recommend that you set the duration to more than 10 minutes. If the related operations succeed within the specified retry duration, the migration task automatically resumes. Otherwise, the task fails. Important The value of Retry Time for Other Issues must be less than the value of Retry Time for Failed Connections.
      Enable Throttling for Full Data Migration	During full migration, DTS consumes read and write resources on the source and destination databases, which may increase the database load. If required, you can enable throttling for the full migration task. You can set Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) to reduce the load on the destination database. Note This configuration item is available only if you select Full Data Migration for Migration Types. You can also adjust the full migration speed after the migration instance is running.
      Only one data type for primary key _id in a table of the data to be synchronized	Indicates whether the data type of the primary key _id is unique within the same collection for the data to be migrated. Important Select an option based on your requirements. Otherwise, data loss may occur. This parameter is available only if you select Full Data Migration for Migration Types. Yes: The data type is unique. During full data migration, DTS does not scan the data types of primary keys in the source data. For a single collection, DTS migrates only the data corresponding to one primary key data type. No: The data type is not unique. During full data migration, DTS scans the data types of primary keys in the source data and migrates all data.
      Enable Throttling for Incremental Data Migration	If required, you can also choose to set speed limits for the incremental migration task. You can set RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) to reduce the load on the destination database. Note This configuration item is available only if you select Incremental Data Migration for Migration Types. You can also adjust the incremental migration speed after the migration instance is running.
      Environment Tag	You can select an environment tag to identify the instance based on your requirements. No tag is required for 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	Select whether to set alerts and receive alert notifications based on your business needs. No: Does not set an alert. Yes: Configure alerts by setting an alert threshold and an alert notifications. If a migration fails or the latency exceeds the threshold, the system sends an alert notification.

6. Save the task and run a precheck.

   • To view the parameters for configuring this instance when you call the API operation, move the pointer over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the bubble that appears.

   • If you do not need to view or have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.

   Note

   • Before the migration task starts, DTS performs a precheck. The task starts only after it passes the precheck.

   • If the precheck fails, click View Details next to the failed check item, fix the issue based on the prompt, and then run the precheck again.

   • If a warning is reported during the precheck:

     • For check items that cannot be ignored, click View Details next to the failed item, fix the issue based on the prompt, and then run the precheck again.

     • For check items that can be ignored, you can click Confirm Alert Details, Ignore, OK, and Precheck Again to skip the alert item and run the precheck again. If you choose to ignore a warning, it may cause issues such as data inconsistency and pose risks to your business.

7. Purchase the instance.

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

   2. On the Purchase page, select the link specification for the data migration instance. For more information, see the following table.

      Category	Parameter	Description
      New Instance Class	Resource Group Settings	Select the resource group to which the instance belongs. The default value is default resource group. For more information, see What is Resource Management?
      	Instance Class	DTS provides migration specifications with different performance levels. The link specification affects the migration speed. You can select a specification based on your business scenario. For more information, see Data migration link specifications.

   3. After the configuration is complete, read and select Data Transmission Service (Pay-as-you-go) Service Terms.

   4. Click Buy and Start. In the OK dialog box that appears, click OK.

      You can view the progress of the migration task on the Data Migration Tasks list page.

      Note

      • If the migration task does not include incremental migration, it stops automatically after the full migration is complete. After the task stops, its Status changes to Completed.

      • If the migration task includes incremental migration, it does not stop automatically. The incremental migration task continues to run. While the incremental migration task is running, the Status of the task is Running.

Data type mapping

Assignment configuration example

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