Data Transmission Service：Migrate data from an ApsaraDB for MongoDB instance to a Lindorm instance

Prerequisites

• Only migration tasks within the Germany (Frankfurt) region are supported.

• The ApsaraDB for MongoDB instance is deployed in the replica set or sharded cluster architecture.

  Important

  If the source instance is an ApsaraDB for MongoDB sharded cluster instance, endpoints are assigned to the shard nodes and the shard nodes share the same account and password. For more information, see Apply for an endpoint for a shard node or the ConfigServer node in a sharded cluster instance.

• A Lindorm instance is created and the wide table engine is used. For more information, see Create an instance.

• A wide table is created in the Lindorm instance. For more information, see Use Lindorm-cli to connect to and use LindormTable and Use Lindorm Shell to connect to LindormTable.

  Note

  If the wide table is created by calling the Apache HBase API, we recommend that you create column mappings. For more information, see the Example of adding column mappings for a table created by calling the Apache HBase API section of this topic.

• The available storage space of the destination instance is 10% larger than the total size of the data in the source instance. This is a recommended prerequisite.

Usage notes

Billing

Migration types

Permissions required for database accounts

Procedure

In this example, a wide table created by executing SQL statements in the Lindorm instance is used.

1. Go to the Data Migration Tasks page.

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

   2. In the top navigation bar, move the pointer over DTS.

   3. Choose DTS (DTS) > Data Migration.

   Note

   You can also go to the Data Migration Tasks page of the new DTS console.

2. From the drop-down list next to Data Migration Tasks, select the region in which the source instance resides.

   Note

   If you use the new DTS console, select the region where your data migration instance resides in the upper-left corner.

3. Click Create Task. In the Create Data Migration Task wizard, configure the source and destination databases. The following table describes the parameters.

   Section	Parameter	Description
   N/A	Task Name	The name of the DTS task. DTS automatically generates a task name. 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 use 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 configure the following database information.
   	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.
   	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. Select No.
   	Architecture	The architecture in which the source instance is deployed. In this example, Replica Set is selected. Note If the source ApsaraDB for MongoDB instance is deployed in the sharded cluster architecture, you must configure the Shard Account and Shard Password parameters.
   	Instance ID	The ID of the source ApsaraDB for MongoDB instance.
   	Authentication Database	The name of the authentication database that stores the database accounts and passwords of the source ApsaraDB for MongoDB instance. If you did not change the name of the authentication database before, the default value is admin.
   	Database Account	The database account of the source ApsaraDB for MongoDB instance.
   	Database Password	The password that is used to access the database instance.
   Destination Database	Select an existing DMS database instance	The database instance that you want to use. You can choose whether to use 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 configure the following database information.
   	Database Type	The type of the destination database. Select Lindorm.
   	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
   	Instance Region	The region in which the destination Lindorm instance resides.
   	Instance ID	The ID of the destination Lindorm instance.
   	Database Account	The database account of the destination Lindorm instance.
   	Database Password	The password that is used to access the database instance.

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 IP address 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 make sure that the ECS instance can access the database. If the self-managed database is hosted on multiple ECS instances, you must manually add the CIDR blocks of DTS servers to the security group rules of each ECS instance. 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 IP address whitelist of the database to allow DTS to access the database. For more information, see the CIDR blocks of DTS servers section of the Add the CIDR blocks of DTS servers topic.

   Warning

   If the public CIDR blocks of DTS servers are automatically or manually added to the whitelist of a database instance or to the security group rules of an ECS instance, security risks may arise. Therefore, before you use DTS to migrate 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 security group rules and forbidding unauthorized CIDR blocks, or connecting the database instance to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

5. Configure the objects to be migrated.

   Parameter	Description
   Migration Types	To perform only full data migration, select only Full Data Migration. To ensure service continuity during data migration, select Full Data Migration and Incremental Data Migration. Note If you do not select Incremental Data Migration, we recommend that you do not write data to the source database during data migration. This ensures data consistency between the source and destination databases.
   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 names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started. Note If the source and destination databases contain collections with identical names and the collections in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the collections that are migrated to the destination database. For more information, see Map object names. 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 consistency is not ensured and your business may be exposed to potential risks. DTS does not migrate data records that have the same primary keys as data records in the destination database. Data may fail to be initialized, only specific columns are migrated, or the data migration task fails.
   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 the collections that you want to migrate in the Source Objects section and click the icon to move the collections to the Selected Objects section.
   Selected Objects	If the wide table in the destination database is created by executing SQL statements, create required columns in the table based on the objects to be migrated from the source instance. Columns that exist in the source instance but are not created in the table are not migrated to the destination database. Edit the schema name. In the Selected Objects section, right-click the database that contains the collections to be migrated. In the Edit Schema dialog box, enter the database name that you want to use in the Lindorm instance in the Schema Name field. Optional. In the Select DDL and DML Operations to Be Synchronized section, you can select the operations that you want to migrate during incremental data migration. Click OK. Edit table names. In the Selected Objects section, right-click a collection to be migrated. In the Edit Table Name dialog box, enter the table name that you want to use in the Lindorm instance in the Table Name field. Optional. You can specify conditions to filter data. For more information, see Specify filter conditions. Optional. In the Select DDL and DML Operations to Be Synchronized section, you can select the operations that you want to migrate during incremental data migration. Specify the columns to be migrated from the source ApsaraDB for MongoDB instance. Click + Add Column. Specify Column Name. Note Enter the column names that you want to use in the destination table in the Lindorm instance. If the destination table is created by executing SQL statements, specify these column names as the value of the Column Name parameter. If the destination table is created by calling the Apache HBase API and additional columns are required, you must create column mappings before you edit column names. For more information, see the Example of adding column mappings for a table created by calling the Apache HBase API section of this topic. Take note of the following rules when you specify the Column Name parameter: If a column is a primary key, specify ROW as the column name. If a column is not a primary key, specify the Column Name parameter in the Column family:Column name format. Example: person:name. Set the data type for each column. Optional. Set the data length and precision for each column. Enter bson_value() expressions in the Assign Value column. For more information, see the Example of value assignment section of this topic. Important You must specify the field and subfield of each column in the corresponding bson_value() expression based on the hierarchical relationship. Otherwise, data loss may occur or the task may fail. Repeat the preceding steps to map the columns of the source table onto the columns of the destination table. Click OK.

6. Click Next: Advanced Settings to configure advanced settings. The following table describes the parameters.

   Parameter	Description
   Dedicated Cluster for Task Scheduling	By default, DTS schedules the data migration task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data migration tasks, purchase a dedicated cluster. For more information, see What is a DTS dedicated cluster.
   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 receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see the Configure monitoring and alerting when you create a DTS task section of the Configure monitoring and alerting topic.
   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 the earliest opportunity after the source database and destination instance are released.
   Retry Time for Other Issues	The retry time range for other issues. For example, if DDL or DML operations fail to be performed after the data migration task is started, DTS immediately retries the operations within the retry time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set the parameter to a value greater than 10. If the failed operations are successfully performed within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Important The value of the Retry Time for Other Issues parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
   Enable Throttling for Full Data Migration	Specifies whether to enable throttling for full data migration. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. You can enable throttling for full data migration based on your business requirements. To configure throttling, you must configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Full Data Migration for the Migration Types parameter.
   Enable Throttling for Incremental Data Migration	Specifies whether to enable throttling for incremental data migration. To configure throttling, you must configure the RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Incremental Data Migration for the Migration Types parameter.
   Environment Tag	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements. In this example, you do not need to configure this parameter.
   Configure ETL	Specifies whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature. Note If the destination table in the Lindorm instance is created by calling the Apache HBase API, take note of the following items: You must specify the columns to be migrated and those not to be migrated in the ETL script. By default, the top-level fields of the specified documents in the ETL task are stored in the f column family of the table created by calling the Apache HBase API during data migration. The following code shows how to write data rows of columns other than _id and name as dynamic columns to the destination table. For more information, see the Example of configuring an ETL task for a table created by calling the Apache HBase API section of this topic. script:e_expand_bson_value("*", "_id,name") If you want to add additional columns and use the ETL feature, make sure that the Lindorm instance does not contain duplicate data. DTS does not migrate the additional columns or columns that are not contained in the ETL task.

7. Click Next: Save Task Settings and Precheck in the lower part of the page.

   Note

   • Before you can start the data migration task, DTS performs a precheck. You can start the data migration 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 analyze the causes based on the check results, troubleshoot the issues. Then, 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 the 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 Instance Class parameter for the data migration instance. The following table describes the parameters.

   Section	Parameter	Description
   New Instance Class	Resource Group	The resource group to which the data migration instance belongs. Default value: default resource group. For more information, see What is Resource Management?
   	Instance Class	DTS provides instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Instance classes of data migration instances.

10. Read and select Data Transmission Service (Pay-as-you-go) Service Terms.

11. Click Buy and Start. In the message that appears, click OK.

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

Example of adding column mappings for a table created by calling the Apache HBase API

1. Create a column mapping for the table created by calling the Apache HBase API:

   ALTER TABLE test MAP DYNAMIC COLUMN f:_mongo_id_ HSTRING/HINT/..., person:name HSTRING, person:age HINT;

2. Create a secondary index for the table created by calling the Apache HBase API:

   CREATE INDEX idx ON test(f:_mongo_id_);

Example of configuring an ETL task for a table created by calling the Apache HBase API

A document in the source ApsaraDB for MongoDB instance

{
  "_id" : 0,
  "person" : {
    "name" : "cindy0",
    "age" : 0,
    "student" : true
  }
}

ETL syntax

script:e_expand_bson_value("*", "_id")

Migration result

Example of value assignment

Data structure of the source ApsaraDB for MongoDB instance

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

Schema of the destination table in the Lindorm instance.

Configuration of additional columns