MongoDB synchronization to Lindorm - Data Transmission Service

Data Transmission Service (DTS) enables the synchronization of MongoDB (ReplicaSet or sharded cluster architecture) to Lindorm (wide table engine). Lindorm provides stability, cost-efficiency, and ease of use, supporting high concurrency, low latency, and reliable system services for use cases such as metadata, orders, billing, profiles, and social networking.

Prerequisites

ApsaraDB for MongoDB is situated in Frankfurt, Germany.
ApsaraDB for MongoDB utilizes either a ReplicaSet or a sharded cluster architecture.

Important
If the source database employs a sharded cluster architecture from ApsaraDB for MongoDB, you must obtain connection addresses for all shard nodes and ensure that the account and password for each shard are consistent. For instructions on how to apply, see Request Shard or ConfigServer node connection addresses.
An instance of Lindorm with more storage space than the source ApsaraDB for MongoDB has been established, utilizing the wide table engine. For instructions on how to create an instance, see Create an instance.

Note
The storage space of the destination instance should be at least 10% larger than that used by the source database.
A wide table has been created in Lindorm to meet business requirements. For instructions on how to create one, see how to connect and use the wide table engine via Lindorm-cli or how to access the wide table engine using Lindorm Shell.

Note
If you create a wide table in Lindorm using HBase, it's advisable to establish column mapping relationships (meaning the wide table's columns function as ordinary columns). For more information, see how to add column mapping for HBase tables.

Notes

Type	Description
Source database limitations	Bandwidth requirements: The server to which the source database is deployed must have sufficient outbound bandwidth. Otherwise, the data synchronization speed is affected. The collections to be synchronized must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records. If the source MongoDB is a sharded cluster architecture instance, the _id field in the collections to be synchronized must be unique. Otherwise, data inconsistency may occur. If the source MongoDB is a sharded cluster architecture instance, the number of Mongos nodes cannot exceed 10. If you select collections as the objects to be synchronized and you need to edit collections in the destination database, such as renaming collections, up to 1,000 collections can be synchronized in a single data synchronization task. If you run a task to synchronize more than 1,000 collections, a request error occurs. In this case, we recommend that you configure multiple tasks to synchronize the collections in batches, or configure a task to synchronize the entire database. The size of a single data entry to be synchronized from the source database cannot exceed 16 MB. Otherwise, the task fails. The source database cannot be an Azure Cosmos DB for MongoDB cluster or an Amazon DocumentDB elastic cluster. The oplog feature must be enabled for the source database and must retain log data for at least seven days. Alternatively, change streams must be enabled to ensure that DTS can subscribe to data changes in the source database within the last seven days. Otherwise, DTS may fail to obtain data changes in the source database and data synchronization fails. In some circumstances, data inconsistency or data loss may occur. Issues that arise in such circumstances are not covered by the service level agreement (SLA) of DTS. Important We recommend that you use the oplog to record data changes in the source database. Only MongoDB 4.0 and later allow you to use change streams to obtain data changes in the source database. Two-way synchronization is not supported when you use change streams to obtain data changes in the source database. If the source database is a non-elastic Amazon DocumentDB cluster, you must enable change streams and set the Migration Method parameter to ChangeStream and the Architecture parameter to Sharded Cluster. Source database operation restrictions: During the full synchronization phase, do not perform schema changes on the database or collections (including updates to array-type data). Otherwise, the data migration task will fail or the data in the source and destination databases will be inconsistent. If only full data synchronization is performed, do not write new data to the source instance. Otherwise, the data in the source and destination databases will be inconsistent. You cannot synchronize collections that contain time to live (TTL) indexes. If the source database contains TTL indexes, data inconsistency may occur between the source and destination databases after the synchronization. Ensure that there are no orphaned documents in the MongoDB instance with a sharded cluster architecture. Otherwise, data inconsistency or even task failure may occur. For more information, see Orphaned Documents and How to clean orphaned documents in MongoDB (sharded cluster architecture). If the source database is a MongoDB with a sharded cluster architecture and the balancer of the source database has balancing data behavior, it may cause instance latency.
Other limitations	Currently, only synchronization tasks between regions in Germany (Frankfurt) are supported. Synchronization of data in the admin and local databases is not supported. The collections in the destination Lindorm cannot have fields named _id and _value. Otherwise, synchronization will fail. If you need to incrementally synchronize UPDATE or DELETE operations, there are the following limitations: If the wide table is created through Lindorm SQL, you must add a non-primary key column _mongo_id_ when creating the table. The type is determined by the type of _id in MongoDB, and a secondary index needs to be created for this column. If the wide table is created through the HBase interface, you must add a non-primary key column with a column family of f _mongo_id_ when creating the table. The type is determined by the type of _id in MongoDB, and a secondary index needs to be created for this column. If you need to use both the newly added columns and the ETL feature, ensure that the data in Lindorm is not duplicated. Transaction information is not retained. When transactions in the source database are synchronized to the destination database, they will be converted into single records. Before performing data synchronization, evaluate the performance of the source and destination databases. It is recommended to perform data synchronization during off-peak business hours. Otherwise, during full data synchronization, DTS will occupy certain read and write resources of the source and destination databases, which may increase the load on the databases. Because full data synchronization will concurrently execute INSERT operations, causing fragmentation in the collections of the destination database, the storage space of the collections in the destination database will be larger than that of the source instance after full synchronization is completed. Confirm whether the synchronization precision of DTS for columns of data types FLOAT or DOUBLE meets business expectations. DTS reads the values of these columns through `ROUND(COLUMN,PRECISION)`. If the precision is not explicitly defined, the synchronization precision for FLOAT is 38 digits, and for DOUBLE, it is 308 digits. DTS will attempt to resume failed synchronization tasks within seven days. Therefore, before switching business to the destination instance, be sure to end or release the task, or use the `revoke` command to revoke the write permissions of the DTS account for the destination instance. Otherwise, the data in the source database will overwrite the data in the destination instance after the task is automatically resumed. Because the delay time of DTS incremental synchronization is determined by comparing the timestamp of the last data synchronized to the destination database with the current timestamp, if the source database does not perform update operations for a long time, the delay information may be inaccurate. If the delay time displayed by the task is too large, you can perform an update operation on the source database to update the delay information. 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 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 overview

Synchronization type	Link configuration fees
Full data synchronization	Free of charge.
Incremental data synchronization	Charged. For details, see Billing overview.

Synchronization type description

Synchronization type	Description
Full synchronization	Synchronize all historical data of the synchronization objects from the source ApsaraDB for MongoDB to the destination Lindorm. Note Supports full synchronization of data in DATABASE and COLLECTION.
Incremental synchronization	On the basis of full synchronization, synchronize the incremental updates of the source ApsaraDB for MongoDB to the destination Lindorm. Note Only supports incremental synchronization of operations such as inserting, updating, and deleting documents in collections. When a DTS task synchronizes incremental data of a file, Only `$set` command can be synchronously run.

Permissions required for database accounts

Database	Required permissions	Account creation and authorization method
Source ApsaraDB for MongoDB	Read permissions for the database to be synchronized, admin database, and local database.	MongoDB database account permission management
Destination Lindorm	Read and write permissions for the target namespace.	Manage ACL permissions

Procedure

Use one of the following methods to go to the Data Synchronization page and select the region in which the data synchronization instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Synchronization.
3. In the upper-left corner of the page, select the region in which the data synchronization instance resides.
DMS console
Note
The actual operations 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 and choose DTS (DTS) > Data Synchronization.
3. From the drop-down list to the right of Data Synchronization Tasks, select the region in which the data synchronization instance resides.
Click Create Task to go to the task configuration page.
Optional. Click New Configuration Page in the upper-right corner of the page.
Note
- Skip this step if the Back to Previous Version button is displayed in the upper-right corner of the page.
- Specific parameters in the new and previous versions of the configuration page may be different. We recommend that you use the new version of the configuration page.

Configure the source and destination databases. The following table describes the parameters.

Category	Configuration	Description
None	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	The database that you want to use. You can choose whether to use an existing database based on your business requirements. If you select an existing database, DTS automatically populates the parameters for the database. If you do not select an existing database, you must configure the following database information. Note In the DTS console, register a database with DTS on the Database Connections page or the new configuration page. For more information, see Manage database connections. In the DMS console, you can select an existing database from the Select a DMS database instance. drop-down list. You can also click Add DMS Database Instance or go back to the homepage of the DMS console to register a database with DMS. For more information, see Register an Alibaba Cloud database instance and Register a database hosted on a third-party cloud service or a self-managed database.
	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	This example is a synchronization between the same Alibaba Cloud account. Select No.
	Architecture	This example selects Replica Set. Note If your source ApsaraDB for MongoDB is a Sharded Cluster, you also need to fill in the Shard account and Shard password.
	Migration Method	The method used to synchronize 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 synchronize incremental data at a low latency because of a fast log pulling speed. Therefore, we recommend 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	Select the instance ID of the source ApsaraDB for MongoDB.
	Authentication Database	Enter the name of the database to which the database account of the source ApsaraDB for MongoDB instance belongs. If it has not been modified, it is the default admin.
	Database Account	Enter the database account of the source ApsaraDB for MongoDB instance. For permission requirements, see Permissions required for database accounts.
	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	The database that you want to use. You can choose whether to use an existing database based on your business requirements. If you select an existing database, DTS automatically populates the parameters for the database. If you do not select an existing database, you must configure the following database information. Note In the DTS console, register a database with DTS on the Database Connections page or the new configuration page. For more information, see Manage database connections. In the DMS console, you can select an existing database from the Select a DMS database instance. drop-down list. You can also click Add DMS Database Instance or go back to the homepage of the DMS console to register a database with DMS. For more information, see Register an Alibaba Cloud database instance and Register a database hosted on a third-party cloud service or a self-managed database.
	Database Type	Select Lindorm.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination Lindorm resides.
	Instance ID	Select the instance ID of the destination Lindorm.
	Database Account	Enter the database account of the destination Lindorm. For permission requirements, see Permissions required for database accounts.
	Database Password	The password that is used to access the database.

Click Test Connectivity and Proceed in the lower part of the page.
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 synchronized.

In the Configure Objects step, configure the objects that you want to synchronize.

Configuration	Description
Synchronization Types	By default, Incremental Data Synchronization is selected. You can select only Full Data Synchronization. You cannot select Schema Synchronization. After the precheck is complete, DTS synchronizes the historical data of the selected objects from the source database to the destination database. The historical data is the basis for subsequent incremental synchronization.
Processing Mode of Conflicting Tables	No configuration is required. Keep the default settings.
Capitalization of Object Names in Destination Instance	The capitalization of database names and collection names in the destination instance. By default, DTS default policy is selected. You can select other options to ensure that the capitalization of object names is consistent with the default capitalization of object names in the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.
Source Objects	Select one or more objects from the Source Objects section and click the icon to add the objects to the Selected Objects section. Note The selection granularity of synchronization objects is at the collection level.
Selected Objects	If the wide table in the destination database is created through Lindorm SQL, you need to synchronize data by configuring newly added columns. Columns that are not configured will not be synchronized to the destination database. Edit schema name mapping. Right-click the library containing the Selected Objects you want to synchronize. Modify the Schema Name to match the name of the target database in Lindorm. Optional: In Select DML Operations to Be Synchronized, choose the operations necessary for incremental synchronization. Click Confirm . Edit table name mapping. Right-click the collection you want to synchronize within the Selected Objects area. Change the Table Name to the name of your target table in Lindorm. Optional: Configure filter conditions. For instructions on how to do this, see Setting Filter Conditions. Optional: In Select DML Operations to Be Synchronized, choose the operations necessary for incremental synchronization. Configure the fields to be synchronized in MongoDB. DTS automatically maps the data from the collections set to sync. In the Assignment column, configure the expressions. Ensure that these expressions align with your requirements and provide details for fields such as Column Name, Type, Length, and Precision. In the Assignment column, you can view the field name corresponding to the row data in MongoDB using the `bson_value()` expression. The `""` represents a field name in MongoDB. For instance, when using the expression `bson_value("age")`, it refers to the row data for the `age` field within MongoDB. Optional: Delete fields that do not need to be synchronized. Note For fields that do not need to be synchronized, you can click after the row data. Configure the fields to be synchronized. Proceed with subsequent operations if the `bson_value()` expression meets your requirements. Fields with expressions that meet the requirements Fill in the Column Name. Note Enter the column name of the target table in Lindorm here. If you created the target table using SQL, enter its column name in Lindorm in the Column Name field. If you are using HBase to create the target table and want to utilize the new column feature, it is necessary to establish column mapping relationships beforehand. To modify the column name, refer to Example of adding column mapping for HBase tables. The Column Name content is detailed below: If the column serves as a primary key, enter ROW . If the column is not a primary key, use the format `column family:column name`, such as person:name . Select the Type of column data. Important Ensure that the data type of the target table is compatible with the data in the source MongoDB. Optional: You can configure the Length and Precision settings for the column data. Repeat the above operations to map the relevant fields one by one. Fields with expressions that do not meet the requirements Note For example, fields with hierarchical relationships (parent-child structures). In the Operation column, click the icon following the row data. Click the + Add Column button. Configure the Column Name, Type, Length, and Precision settings. In the text box below Assignment, enter the `bson_value()` expression. For more information, see the example of assignment configuration. Important The target table's primary key column must be set to `bson_value("_id")`. When setting up the `bson_value()` expression, ensure it targets the most granular subfield based on the hierarchy to prevent data loss or task failure. Repeat the above operations to map the relevant fields one by one. Click the Confirm button.

Click Next: Advanced Settings to configure advanced settings.

Configuration	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data synchronization 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 synchronization task is started, DTS immediately retries a connection within the time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set this parameter to a value greater than 30. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Note If you specify different retry time ranges for multiple data synchronization tasks that have the same source or destination database, the shortest retry time range takes precedence. When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
Retry Time for Other Issues	The retry time range for other issues. For example, if the DDL or DML operations fail to be performed after the data synchronization task is started, DTS immediately retries the operations within the time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set this parameter to a value greater than 10. If the failed operations are successfully performed within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization 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	During full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the load on the database servers. You can 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 for full data synchronization tasks to reduce the load on the destination database server. Note This parameter is displayed only if Full Data Synchronization is selected for the Synchronization Types parameter.
Only one data type for primary key _id in a single table	Whether the data type for primary key `_id` in a collection of the data to be synchronized is unique. Valif value: Note This parameter is displayed only if Full Data Synchronization is selected for the Synchronization Types parameter. Yes: The data type is unique. During full data synchronization, DTS does not scan the data type for primary key `_id` of the data to be synchronized from the source database. No: The data type is not unique. During full data synchronization, DTS scans the data type for primary key `_id` of the data to be synchronized from the source database.
Enable Throttling for Incremental Data Synchronization	Specifies whether to enable throttling for incremental data synchronization. You can enable throttling for incremental data synchronization based on your business requirements. To configure throttling, you must configure the RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s) parameters. This reduces the load on the destination database server.
Environment Tag	You can select an environment tag to identify the instance based on your actual situation. In this example, no environment tag is selected.
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 target table is created using HBase, consider the following: The ETL syntax encompasses columns to be configured along with those to be omitted. During sync, all top-level fields of MongoDB documents configured for ETL are stored in the default HBase column family 'f'. The example below demonstrates that all elements, with the exception of the two top-level elements _id and name, are written as dynamic columns in the destination table. For more information, see the HBase table synchronization example (ETL). `script:e_expand_bson_value("*", "_id,name")` If you need to use both the newly added columns and the ETL feature, ensure that the data in Lindorm is not duplicated. Columns that are not configured with the newly added columns and the ETL feature will not be synchronized to the destination database.
Monitoring and Alerting	Specifies whether to configure alerting for the data synchronization task. If the task fails or the synchronization latency exceeds the specified threshold, alert contacts will receive notifications. Valid values: No: does not enable 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 synchronization task, DTS performs a precheck. You can start the data synchronization task only after the task passes the precheck.
- If the data synchronization task fails the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, rerun the precheck.
- 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 issue. Then, run a precheck again.
  If an alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur, and your business may be exposed to potential risks.

Purchase an instance.

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

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

Section	Parameter	Description
New Instance Class	Billing Method	Subscription: You pay for a subscription when you create a data synchronization instance. The subscription billing method is more cost-effective than the pay-as-you-go billing method for long-term use. Pay-as-you-go: A pay-as-you-go instance is billed on an hourly basis. The pay-as-you-go billing method is suitable for short-term use. If you no longer require a pay-as-you-go data synchronization instance, you can release the instance to reduce costs.
	Resource Group Settings	The resource group to which the data synchronization instance belongs. Default value: default resource group. For more information, see What is Resource Management?
	Instance Class	DTS provides instance classes that vary in synchronization speed. You can select an instance class based on your business requirements. For more information, see Instance classes of data synchronization instances.
	Subscription Duration	If you select the subscription billing method, specify the subscription duration and the number of data synchronization instances that you want to create. The subscription duration can be one to nine months, one year, two years, three years, or five years. Note This parameter is available only if you select the Subscription billing method.

Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start. In the dialog box that appears, click OK.
You can view the progress of the task in the task list.

Example of adding column mapping for HBase tables

This example demonstrates how to use SQL Shell to add column mapping.

Note

Lindorm must be version 2.4.0 or later.

Add column mapping to the table created by HBase.

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

Add a secondary index to the table created by HBase.
```
CREATE INDEX idx ON test(f:_mongo_id_);
```

HBase table synchronization example (ETL)

MongoDB Document

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

ETL Data Processing Statement

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

Synchronization Result

迁移结果

Example of assignment configuration

Source MongoDB Data Structure

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

Target Lindorm Table Structure

Column Name	Type
id	STRING
person_name	STRING
person_age	INT

New Column Configuration

Important

Ensure that the bson_value() expression is correctly configured to reflect the hierarchical relationship; otherwise, data loss or task failure may occur. For instance, configuring the expression as bson_value("person") means DTS will be unable to write the incremental change data for subfields such as name, age, or sex of the person field in the source to the target.

Column Name	Type	Assignment
id	STRING	bson_value("_id")
person_name	STRING	bson_value("person","name")
person_age	BIGINT	bson_value("person","age")