Synchronize MongoDB data to AnalyticDB for PostgreSQL - Data Transmission Service

Data Transmission Service (DTS) supports the synchronization of MongoDB data to an AnalyticDB for PostgreSQL instance. This guide details the steps for synchronizing data from an ApsaraDB for MongoDB instance with a ReplicaSet architecture to AnalyticDB for PostgreSQL.

Prerequisites

A target AnalyticDB for PostgreSQL instance with storage space larger than the storage space occupied by the source ApsaraDB for MongoDB instance has been created. For more information, see Create an instance.
Note
It is recommended that the storage space of the target instance be 10% larger than the storage space used by the source database.
A database, schema, and tables with primary keys have been created in the target AnalyticDB for PostgreSQL instance to receive data. For more information, see SQL syntax.
Important
- Ensure that the data types of the target tables are compatible with the data in the source MongoDB. For example, if the _id in MongoDB is of the ObjectId type, the corresponding data type in the AnalyticDB for PostgreSQL instance must be varchar.
- The column names of the target tables in the AnalyticDB for PostgreSQL instance cannot be _id and _value.
If the source is a sharded cluster architecture of ApsaraDB for MongoDB, you must apply for connection addresses for all shard nodes, and the accounts and passwords of each shard must be consistent. For more information, see Apply for shard or ConfigServer node connection addresses.

Notes

Type	Description
Source database limitations	Bandwidth requirements: The server where the source database resides must have sufficient outbound bandwidth. Otherwise, the data synchronization speed will be affected. If you need to perform editing (such as collection name mapping), a single synchronization task supports synchronizing up to 1,000 collections. If the number exceeds the limit, a request error will be displayed after the task is submitted. In this case, we recommend that you split the collections to be synchronized, configure multiple tasks in batches, or configure a task to synchronize the entire database. 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 source Mongos nodes cannot exceed 10. Also, ensure that there are no orphaned documents in the sharded cluster architecture MongoDB instance. 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). The source database does not support standalone architecture MongoDB, Azure Cosmos DB for MongoDB, and elastic cluster Amazon DocumentDB. 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 limitations: During the full synchronization phase, do not perform schema changes (including updates to array-type data) on the database or collections. Otherwise, the data synchronization task will fail, or the data in the source and target databases will be inconsistent. If you only perform full data synchronization, do not write new data to the source instance. Otherwise, the data in the source and target databases will be inconsistent. To maintain data consistency in real-time, we recommend selecting both full data synchronization and incremental data synchronization. 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	Only collection-level synchronization is supported. The table in the target AnalyticDB for PostgreSQL instance that receives data must have a unique primary key column (not a composite primary key). When configuring synchronization fields in Selected Objects, the primary key column's Assignment must be `bson_value("_id")`. The table in the target AnalyticDB for PostgreSQL instance that receives data cannot have fields named _id and _value. Otherwise, synchronization will fail. If the data type in the AnalyticDB for PostgreSQL instance is not compatible with MongoDB data, the task will fail. Synchronization of data in the admin and local databases is not supported. AO tables are not supported in the target table. 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.

Pricing

Synchronization type	Link configuration fee
Full data synchronization	Free of charge.
Incremental data synchronization	Charged. For more information, see Billing overview.

Synchronization type description

Synchronization type	Description
Full synchronization	Synchronizes all historical data of the objects in the source ApsaraDB for MongoDB to the target AnalyticDB for PostgreSQL instance.
Incremental synchronization	Based on full synchronization, synchronizes incremental updates from the source ApsaraDB for MongoDB to the target AnalyticDB for PostgreSQL instance. 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 on the databases to be synchronized, admin database, and local database.	MongoDB database account permission management
Target AnalyticDB for PostgreSQL	Read and write permissions on the target database.	Create and manage users and User permission management. Note You can use the initial account or an account with RDS_SUPERUSER 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 Development 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 resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database of the current Alibaba Cloud account is used. Select No.
	Architecture	In this example, select 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. 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 AnalyticDB for PostgreSQL.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the target AnalyticDB for PostgreSQL instance resides.
	Instance ID	Select the instance ID of the target AnalyticDB for PostgreSQL instance.
	Database Name	Enter the name of the database in the target AnalyticDB for PostgreSQL instance that receives the synchronization objects.
	Database Account	Enter the database account of the target AnalyticDB for PostgreSQL instance. 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.
DDL and DML Operations to Be Synchronized	Select the operations for incremental synchronization at the instance level. Note To select operations for incremental synchronization at the collection level, right-click the object in Selected Objects and choose from the options in the pop-up box.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that have the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck, and the data synchronization task cannot be started. Note If the source and destination databases contain tables with identical names and the tables in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the tables that are synchronized to the destination database. For more information, see Map object names. Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to potential risks. If the source and destination databases have the same schema and a data record in the destination database has the same primary key value or unique key value as a data record in the source database: During full data synchronization, DTS does not synchronize the data record to the destination database. The existing data record in the destination database is retained. During incremental data synchronization, DTS synchronizes the data record to the destination database. The existing data record in the destination database is overwritten. If the source and destination databases have different schemas, data may fail to be initialized. In this case, only some columns are synchronized, or the data synchronization task fails. Proceed with caution.
```html 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 granularity for selecting synchronization objects is at the collection level.
Selected Objects	Edit the schema name mapping. Right-click the database containing the collection to be synchronized in Selected Objects. Change the Schema Name to the corresponding schema name in the target AnalyticDB for PostgreSQL instance. Optional: In the Select DDL and DML Operations to Be Synchronized section, choose the operations you want to incrementally sync. Click OK. Edit the table name mapping. Right-click the collection to be synchronized in Selected Objects. Change the Table Name to the corresponding table name in the target AnalyticDB for PostgreSQL instance. Optional: Define filter conditions. For more information, see how to set filter conditions. Optional: In the Select DDL and DML Operations to Be Synchronized area, you can choose the operations you want to incrementally sync. Configure the MongoDB fields for synchronization. By default, DTS maps the data from the collections to be synchronized and configures expressions in the Assignment column. Verify that the expressions meet your requirements and configure details such as Column Name, Type, Length, and Precision. In the Assignment column, review the MongoDB field name within the `bson_value()` expression. The field within `""` is the MongoDB field name. For example, if the expression is `bson_value("age")`, the corresponding MongoDB field is `age`. Optional: Remove fields that are not required for synchronization. Note For fields that are not required, click after the row of data to remove them. Configure the fields for synchronization. Proceed based on whether the `bson_value()` expression meets your requirements. Fields with expressions that meet the requirements Enter the Column Name. Note This is the column name in the target AnalyticDB for PostgreSQL instance. Select the Type for the column data. Important Ensure the target table's data types are compatible with the source MongoDB data. Optional: Set the Length and Precision for the column data. Map the relevant fields one by one. Fields with expressions that do not meet the requirements Note This includes fields with hierarchical relationships (parent-child structures). In the Operation column, click after the row of data. Click + Add Column. Configure the Column Name, Type, Length, and Precision. In the textbox below Assignment, enter the `bson_value()` expression. For more information, see Assignment Configuration Example. Important The primary key column of the target table must be assigned as `bson_value("_id")`. When configuring the `bson_value()` expression, ensure it is set to the smallest subfield according to the hierarchical relationship to avoid data loss or task failure. Map the relevant fields one by one. Click OK.

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.
```html 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	Select an environment tag to categorize the instance according to your needs. 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.
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.

Assignment Configuration Example

Data structure of the source MongoDB

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

Table structure of the target AnalyticDB for PostgreSQL Table structure

Column name	Type
mongo_id	varchar Note Primary key column.
person_name	varchar
person_age	decimal

New column configuration

Important

Ensure the bson_value() expression is configured correctly to reflect the hierarchical relationship, to prevent data loss or task failure. For instance, configuring the expression as bson_value("person") means DTS cannot write incremental changes of subfields such as name, age, or sex within the person field from the source to the target.

Column name	Type	Assignment
mongo_id	STRING	bson_value("_id")
person_name	STRING	bson_value("person","name")
person_age	DECIMAL	bson_value("person","age")