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

This topic describes how to migrate data from an ApsaraDB for MongoDB replica set or sharded cluster instance to a Lindorm instance by using Data Transmission Service (DTS).

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.
A Lindorm instance is created and the wide table engine is used. For more information, see Create an instance.
Note
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.
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
- The objects that you create must comply with the requirements described in the topic Quotas and limits.
- 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.

Usage notes

Category	Description
Limits on the source database	The server on which the source database is deployed must have sufficient outbound bandwidth. Otherwise, the data migration speed decreases. The collections to be migrated 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 migrated and you want to modify the collections such as renaming the collections, you can migrate up to 1,000 collections in a single data migration task. If you run a task to migrate more than 1,000 collections, a request error occurs. In this case, we recommend that you configure multiple tasks to migrate the collections in batches. If the source database is an Azure Cosmos DB for MongoDB cluster or an Amazon DocumentDB elastic cluster, only full data migration is supported. To perform incremental data migration, you must make sure that the following requirements are met: The oplog feature is enabled for the source database and operation logs of the source database are retained for at least seven days. Alternatively, change streams are enabled for the source database and DTS can use change streams to subscribe to data changes in the source database within the last seven days. Otherwise, DTS may fail to obtain the operation logs and the data migration task may fail. In exceptional circumstances, data inconsistency or loss may occur. The service level agreement (SLA) of DTS does not cover these issues. Important We recommend that you use the oplog feature to obtain data changes in the source database. You can use change streams to obtain data changes in the source database only if the source database runs MongoDB V4.0 or later. If the source database is an inelastic Amazon DocumentDB cluster, you must enable change streams for the database and set the Migration Method parameter to ChangeStream and the Architecture parameter to Sharded Cluster when you configure the data migration task. If the source instance is an ApsaraDB for MongoDB sharded cluster instance, the _id field in the collections to be migrated must be unique. Otherwise, data inconsistency may occur. If the source instance is an ApsaraDB for MongoDB sharded cluster instance, the number of Mongos nodes in the instance cannot exceed 10. DTS cannot connect MongoDB database over a SRV endpoint. Limits on operations to be performed on the source database: During full data migration, do not perform schema change on databases or collections, including the update of the array type. Otherwise, the data migration task fails, or data inconsistency between the source and destination databases may occur. If you perform only full data migration, do not write data to the source database during data migration. Otherwise, data inconsistency occurs between the source and destination databases. If the source MongoDB instance is deployed in a sharded cluster architecture, do not run commands such as shardCollection, reshardCollection, unshardCollection, moveCollection, and movePrimary to change data distribution for the object to be migrated in the source database when the data migration instance is running. Otherwise, data inconsistency may occur. If the source database contains TTL indexes, data inconsistency may occur between the source and destination databases after the migration. If the source database is a MongoDB with a sharded cluster architecture and the Balancer in the source database has balancing data behavior, it may cause latency in the instance.
Other limits	DTS cannot migrate data from the admin, config, or local database. The destination Lindorm instance cannot contain collections that have the _id or _value column. Otherwise, the data migration task fails. If you want to migrate UPDATE or DELETE operations during incremental data migration, make sure that the following requirements are met: If the wide table is created by executing Lindorm SQL statements, you must add a non-primary key column named _mongo_id_ when you create the table. The data type of the column is determined by that of the _id column in the source ApsaraDB for MongoDB instance. In addition, you must create a secondary index on the non-primary key column. If the wide table is created by calling the Apache HBase API, you must add a non-primary key column named _mongo_id_ whose column family is f when you create the table. The data type of the column is determined by that of the _id column in the source ApsaraDB for MongoDB instance. In addition, you must create a secondary index on the non-primary key column. If you want to add additional columns and use the extract, transform, and load (ETL) feature, make sure that the Lindorm instance does not contain duplicate data. Transaction information is not retained. When transactions are migrated to the destination database, they are converted into a single record. The data to be migrated in the Lindorm instance must meet the requirements specified in Limits on data requests. Otherwise, the task fails. Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. 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. During full data migration, concurrent INSERT operations cause fragmentation in the collections of the destination database. After full data migration is complete, the storage space for collections of the destination database is larger than that of the source database. You must make sure that the precision settings for columns of the FLOAT or DOUBLE data type meet your business requirements. DTS uses the `ROUND(COLUMN,PRECISION)` function to retrieve values from columns of the FLOAT or DOUBLE data type. If you do not specify a precision, DTS sets the precision for the FLOAT data type to 38 digits and the precision for the DOUBLE data type to 308 digits. DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch your workloads to the destination database, you must stop or release the failed tasks. You can also execute the `REVOKE` statement to revoke the write permissions from the accounts that are used by DTS to access the destination database. Otherwise, the data in the source database overwrites the data in the destination instance after the task is automatically resumed. DTS calculates the latency of an incremental data migration based on the timestamp of the latest migrated data in the destination database and the current timestamp in the source database. If no update operation is performed on the source database for an extended period of time, the migration latency may be inaccurate. If the latency of the migration task is excessively high, you can perform an update operation on the source database to update the latency. If a DTS task fails to run, DTS technical support will try to restore the task within 8 hours. During the restoration, the task may be restarted, and the parameters of the task may be modified. Note Only the parameters of the DTS task may be modified. The parameters of databases are not modified. The parameters that may be modified include but are not limited to the parameters in the "Modify instance parameters" section of the Modify the parameters of a DTS instance topic.

Billing

Migration type	Task configuration fee	Data transfer fee
Full Data Migration	Free of charge.	Free of charge in this example. When the Access Method parameter of the destination database is set to Public IP Address, you are charged for Internet traffic. For more information, see Billable items.
Incremental Data Migration	Charged. For more information, see Billing overview.

Migration types

Migration type	Description
Full Data Migration	DTS migrates the existing data of the objects to be migrated from the source ApsaraDB for MongoDB instance to the destination Lindorm instance. Note DTS supports full data migration for databases and collections.
Incremental Data Migration	After full data migration is complete, DTS migrates incremental data from the source ApsaraDB for MongoDB instance to the destination Lindorm instance. Note Only the operations that are performed to insert, update, or delete documents in a collection can be migrated during incremental data migration. When you migrate the incremental data of updated documents, migrate only updates from `$set`.

Permissions required for database accounts

Database type	Full Data Migration	Incremental Data Migration	References
Source ApsaraDB for MongoDB instance	Read permission on the source database.	Read permission on the source database, the admin database, and the local database.	Manage the permissions of MongoDB database users
Destination Lindorm instance	Read and write permissions on the Lindorm instance.		Manage users

Procedure

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

Use one of the following methods to go to the Data Migration page and select the region in which the data migration instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Migration.
3. In the upper-left corner of the page, select the region in which the data migration instance resides.
DMS console
Note
The actual operation may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Customize the layout and style of the DMS console.
1. Log on to the DMS console.
2. In the top navigation bar, move the pointer over Data + AI > DTS (DTS) > Data Migration.
3. From the drop-down list to the right of Data Migration Tasks, select the region in which the data synchronization instance resides.
Click Create Task to go to the task configuration page.

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 Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, 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 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.
	Migration Method	The method used to migrate incremental data from the source database. Select a method based on your business requirements. Valid values: Oplog (recommended): This option is available if the oplog feature is enabled for the source database. Note By default, the oplog feature is enabled for both self-managed MongoDB databases and ApsaraDB for MongoDB instances. This feature allows you to migrate incremental data at a low latency because of a fast log pulling speed. Therefore, we recommended that you select Oplog for the Migration Method parameter. ChangeStream: This option is available if change streams are enabled for the source database. For more information, see Change Streams. Note If the source database is an inelastic Amazon DocumentDB cluster, you can set the Migration Method parameter only to ChangeStream. If you select Sharded Cluster for the Architecture parameter, you do not need to 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.
	Encryption	Specifies whether to encrypt the connection to the source database. You can select Non-encrypted, SSL-encrypted, or Mongo Atlas SSL based on your business requirements. The options available for the Encryption parameter are determined by the values selected for the Access Method and Architecture parameters. The options displayed in the DTS console prevail. Note If the Architecture parameter is set to Sharded Cluster, and the Migration Method parameter is set to Oplog for the ApsaraDB for MongoDB database, the Encryption parameter SSL-encrypted is unavailable. If the source database is a self-managed MongoDB database that uses the Replica Set architecture, the Access Method parameter is not set to Alibaba Cloud Instance, and the Encryption parameter is set to SSL-encrypted, you can upload a certification authority (CA) certificate to verify the connection to the source database.
Destination Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, 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.

In the lower part of the page, click Test Connectivity and Proceed.
Note
- Make sure that the CIDR blocks of DTS servers can be 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 the CIDR blocks of DTS servers.
- If the source or destination database is a self-managed database and its Access Method is not set to Alibaba Cloud Instance, click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

Configure the objects to be migrated.

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

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	You do not need to specify this parameter.
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 another option to ensure that the capitalization of object names is the same as that of 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. DTS defaults to map data of the collection to be migrated and configure an expression in the Assign Value column. You need to check that the expression meets your business requirements and configure parameters such as Column Name, Type, Length, and Precision. View the field name of a column in the ApsaraDB for MongoDB instance in the `bson_value()` expression. The field in the `""` of the expression is the field name in the ApsaraDB for MongoDB instance. For example, if the expression is `bson_value("age")`, the `age` is the field name in the ApsaraDB for MongoDB instance. Optional: You can delete the fields that do not need to be migrated. Note Click the icon next to the column to delete the fields that do not meed to be migrated. Configure fields to be migrated. Check that the `bson_value()` expression meets your business requirements and perform subsequent operations. The expression meets required fields Enter 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. Select Type of the column data. Important Make sure that the data type of the destination table is compatible with the data type in the source ApsaraDB for MongoDB instance. Optional: Specify Length and Precision for the column data. Repeat the preceding steps to map the fields one by one. The expression does not meet required fields Note For example, the fields that displays the hierarchical relationships between parent and child. Click the icon next to the column in the Actions column. Click + Add Column. Specify the Column Name, Type, Length, and Precision parameters. Enter `bson_value()` expression in the Assign Value column. For more information, see Example of value assignment. Important Assign the primary key column of the destination table as `bson_value("_id")`. Specify the field and subfield of each column in the `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 fields one by one. Click OK.

Click Next: Advanced Settings to configure advanced settings.

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.
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 1,440. 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.
Only one data type for primary key _id in a table of the data to be synchronized	Specifies whether the data type of the primary key `_id` is unique in a collection to be migrated. Important Enable this parameter based on your business requirements. Otherwise, data loss may occur. This parameter is required only if you select Full Data Migration for the Migration Types parameter. Valid values: Yes: The data type is unique. During full migration, DTS does not scan the data type of the primary key in source database. No: The data type is not unique. During full migration, DTS scans the data type of the primary key in source database.
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.
Monitoring and Alerting	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.

Save the task settings and run a precheck.
- To view the parameters to be specified when you call the relevant API operation to configure the DTS task, move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters.
- If you do not need to view or have viewed the parameters, 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.

Purchase an instance.

Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.

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?
New Instance Class	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.

Read and agree to Data Transmission Service (Pay-as-you-go) Service Terms by selecting the check box.
Click Buy and Start. In the message that appears, click OK.
You can view the progress of the task on the Data Migration page.
Note
- If a data migration task cannot be used to migrate incremental data, the task automatically stops. The Completed is displayed in the Status section.
- If a data migration task can be used to migrate incremental data, the task does not automatically stop. The incremental data migration task never stops or completes. The Running is displayed in the Status section.

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

In this example, SQL Shell is used.

Note

The engine version of the Lindorm instance must be 2.4.0 or later.

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;

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

迁移结果

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.

Column name	Category
id	STRING
person_name	STRING
person_age	INT

Configuration of additional columns

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. For example, if you specify only the person field of the source column by using the bson_value("person") expression, DTS cannot write the incremental data in the subfields of the person field, such as name, age, and sex, to the destination column.

Column name	Category	Value
id	STRING	bson_value("_id")
person_name	STRING	bson_value("person","name")
person_age	BIGINT	bson_value("person","age")