Synchronize data: ApsaraDB for MongoDB to AnalyticDB for PostgreSQL-Data Transmission Service(DTS)-阿里云帮助中心

Prerequisites

You have created a target AnalyticDB for PostgreSQL instance. Its storage space must be larger than the storage used by the source ApsaraDB for MongoDB instance. For more information, see Create an instance.

Note
The target instance's storage space should be at least 10% larger than the storage used by the source database.
In the target AnalyticDB for PostgreSQL instance, you have created a database, a schema, and a table with a primary key. For more information, see SQL syntax.
Important
- Ensure that the data types in the target table are compatible with the source MongoDB data. For example, if the _id field in MongoDB is of the ObjectId type, the corresponding data type in the AnalyticDB for PostgreSQL instance must be varchar.
- The target table in the AnalyticDB for PostgreSQL instance cannot have columns named _id or _value.
If the source ApsaraDB for MongoDB instance is a sharded cluster, you must obtain endpoints for all shard nodes. The database account and password for each shard must be the same. For more information, see Apply for a shard endpoint.

Notes

Type	Description
Source database limits	Bandwidth requirement: The server where your source database resides must have sufficient outbound bandwidth. Otherwise, synchronization speed may be affected. To edit objects (such as rename collections), one synchronization task supports up to 1,000 collections. If you exceed this limit, the task fails with an error after submission. To resolve this, split the collections into batches and configure multiple tasks. Or configure a full-database synchronization task. If your source MongoDB is a sharded cluster instance, the _id field in the collections to synchronize must have unique values. Otherwise, data inconsistency may occur. If your source MongoDB is a sharded cluster instance, the number of Mongos nodes cannot exceed 10. Also ensure no orphaned documents exist in your MongoDB sharded cluster instance. Otherwise, data inconsistency or task failure may occur. For more information, see orphaned documents and How to clean orphaned documents in MongoDB (sharded cluster architecture). If your source instance is a self-managed MongoDB sharded cluster: Access Method supports only Express Connect, VPN Gateway, or Smart Access Gateway and Cloud Enterprise Network (CEN). If your MongoDB version is 8.0 or later and Migration Method is Oplog, ensure the Shard account used by the synchronization task has the `directShardOperations` permission. Add this permission using the command `db.adminCommand({ grantRolesToUser: "username", roles: [{ role: "directShardOperations", db: "admin"}]})`. Note Replace `username` in the command with the Shard account used by the synchronization task. If Migration Method is Oplog and the task includes full data synchronization, ensure the Mongos account for your source MongoDB sharded cluster has permission to run the `db.runCommand({"balancerStatus":1})` command. DTS checks whether the Balancer is disabled using this command during precheck. Your source database does not support standalone MongoDB, Azure Cosmos DB for MongoDB, or Amazon DocumentDB (elastic cluster). Your source database must enable Oplog and retain Oplog for at least seven days. Or enable Change Streams and ensure DTS can subscribe to data changes in the last seven days through Change Streams. Otherwise, DTS may fail to capture data changes, causing task failure. In extreme cases, this may cause data inconsistency or loss. These issues are not covered by the DTS Service-level agreement (SLA). Important We recommend using Oplog to capture data changes. Only MongoDB 4.0 and later support Change Streams. Change Streams do not support two-way synchronization. If your source database is Amazon DocumentDB (non-elastic cluster), manually enable Change Streams. When you configure the task, set Migration Method to ChangeStream and set Architecture to Sharded Cluster. Source database operation limits: During full data synchronization, do not change the schema of databases or collections (including array-type data updates). Otherwise, the synchronization task may fail or cause data inconsistency between the source and destination databases. If your source MongoDB is a sharded cluster instance, while the synchronization instance is running, do not run commands that change data distribution on the objects to synchronize in the source database (for example, shardCollection, reshardCollection, unshardCollection, moveCollection, or movePrimary). Otherwise, data inconsistency may occur. If your source MongoDB is a sharded cluster and the Balancer balances data, latency may occur. DTS does not support connecting to MongoDB databases using SRV addresses.
Other limits	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 (cannot be a composite primary key). When you configure synchronization fields in the Selected Objects section, the Assignment for this primary key column must be `bson_value("_id")`. The table that receives data in the target AnalyticDB for PostgreSQL instance must not have fields named _id or _value. Otherwise, the synchronization will fail. If the data types in the AnalyticDB for PostgreSQL instance are incompatible with MongoDB data, the task fails. DTS does not support synchronizing data from the admin, config, and local databases. The destination table does not support AO tables. Transaction information is not preserved. Transactions in the source database become individual records in the destination database. Evaluate the performance of both the source and destination databases before synchronization. Run synchronization during off-peak hours. Otherwise, full data synchronization consumes read and write resources, increasing database load. Full data synchronization runs INSERT operations concurrently. This creates fragmentation in the destination database collection. After full synchronization, the collection storage space in the destination database is larger than in the source instance. Confirm that DTS synchronization precision for FLOAT or DOUBLE columns meets your business expectations. DTS reads these columns using `ROUND(COLUMN,PRECISION)`. If precision is not defined, DTS uses 38 digits for FLOAT and 308 digits for DOUBLE. DTS attempts to recover failed synchronization tasks within seven days. Before switching traffic to the destination instance, end or release the task. Or use the `revoke` command to revoke write permissions for the DTS account on the destination instance. This prevents automatic recovery from overwriting destination data with source data. DTS calculates incremental synchronization latency by comparing the timestamp of the last synchronized document with the current timestamp. If the source database has no updates for a long time, latency information may be inaccurate. If latency appears too high, run an update operation in the source database to refresh latency information. DTS does not support synchronizing time-series collections introduced in MongoDB 5.0 and later. If a task fails, DTS support staff will attempt to restore it within eight hours. During restoration, they may restart the task or adjust its parameters. Note Only DTS task parameters are modified—not database parameters. Parameters that may be adjusted include those listed in Modify instance parameters.

Billing

Type	Fee
Full data synchronization	Free.
Incremental data synchronization	Charged. For details, see Billing overview.

Synchronization types

Type	Description
Full data synchronization	A full data synchronization transfers all existing data for selected objects from the source ApsaraDB for MongoDB instance to the destination AnalyticDB for PostgreSQL instance.
Incremental data synchronization	After a full data synchronization is complete, incremental updates from the source ApsaraDB for MongoDB instance are synchronized to the destination AnalyticDB for PostgreSQL instance. Note Incremental data synchronization supports only operations to insert, update, or delete documents in a collection. For document updates, it replicates only operations that use the `$set` command.

Database account permissions

Database	Required permissions	Actions
Source ApsaraDB for MongoDB	Read permission on the databases to be synchronized, the admin database, and the local database.	Manage the permissions of MongoDB database users
Destination AnalyticDB for PostgreSQL	Read and write permissions on the destination database.	Create and manage database accounts and user permission management. Note You can use the initial account or a database account that has the RDS_SUPERUSER permission.

Procedure

Go to the data synchronization task list page in the destination region. You can do this in one of two ways.
DTS console
1. Log on to the DTS console.
2. In the navigation pane on the left, click Data Synchronization.
3. In the upper-left corner of the page, select the region where the synchronization instance is located.
DMS console
Note
The actual steps may vary depending on the mode and layout of the DMS console. For more information, see Simple mode console and Customize DMS console layout and style.
1. Log on to the DMS console.
2. In the top menu bar, choose Data + AI > DTS (DTS) > Data Synchronization.
3. To the right of Data Synchronization Tasks, select the region of the synchronization instance.
Click Create Task to open the task configuration page.

Configure the source and destination databases.

Category	Parameter	Description
N/A	Task Name	DTS automatically generates a task name. We recommend that you specify a descriptive name for easy identification. The name does not need to be unique.
Source Database	Select Existing Connection	Select the registered database instance with DTS from the drop-down list. The database information below is automatically configured. Note In the DMS console, this configuration item is Select a DMS database instance. If you have not registered the database instance or do not need to use a registered instance, manually configure the database information below.
	Database Type	Select MongoDB.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source ApsaraDB for MongoDB instance is located.
	Replicate Data Across Alibaba Cloud Accounts	For this example, select No, as the database instance belongs to the current Alibaba Cloud account.
	Architecture	In this example, select Replica Set. Note If your source ApsaraDB for MongoDB instance uses the Sharded Cluster architecture, you must also specify the Shard account and Shard password.
	Migration Method	Select a method for incremental data synchronization based on your requirements. Oplog (Recommended): This option is available if Oplog is enabled for the source database. Note Oplog is enabled by default for self-managed MongoDB databases and ApsaraDB for MongoDB instances. This method offers lower latency for incremental synchronization tasks because logs are retrieved faster. We recommend selecting Oplog. ChangeStream: This option is available if Change Streams are enabled for the source database. Note If the source database is an Amazon DocumentDB (non-elastic cluster) instance, you can select only ChangeStream. If you set Architecture of the source database to Sharded Cluster, you do not need to specify Shard account and Shard password.
	Instance ID	Select the ID of the source ApsaraDB for MongoDB instance.
	Authentication Database	Enter the name of the database to which the database account of the source ApsaraDB for MongoDB instance belongs. If you have not changed the name, the default value is admin.
	Database Account	Enter the database account of the source ApsaraDB for MongoDB instance. For the required permissions, see Permissions required for database accounts.
	Database Password	Enter the password for the specified database account.
	Encryption	DTS supports three connection methods: Non-encrypted, SSL-encrypted, and Mongo Atlas SSL. The options for Encryption vary based on the selected Access Method and Architecture. The options displayed in the console prevail. Note A MongoDB database where the Architecture is Sharded Cluster and the Migration Method is Oplog does not support SSL-encrypted. If the source is a self-managed MongoDB database (Access Method is not Alibaba Cloud Instance) with a Replica Set architecture, and you select SSL-encrypted, DTS also allows you to upload a CA certificate to verify the connection.
Destination Database	Select Existing Connection	Select the registered database instance with DTS from the drop-down list. The database information below is automatically configured. Note In the DMS console, this configuration item is Select a DMS database instance. If you have not registered the database instance or do not need to use a registered instance, manually configure the database information below.
	Database Type	Select AnalyticDB for PostgreSQL.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination AnalyticDB for PostgreSQL instance is located.
	Instance ID	Select the ID of the destination AnalyticDB for PostgreSQL instance.
	Database Name	Enter the name of the database in the destination AnalyticDB for PostgreSQL instance that will store the synchronized objects.
	Database Account	Enter the database account of the destination AnalyticDB for PostgreSQL instance. For the required permissions, see Permissions required for database accounts.
	Database Password	Enter the password for the specified database account.

After completing the configuration, click Test Connectivity and Proceed at the bottom of the page.
Note
- Ensure that you add the CIDR blocks of the DTS servers (either automatically or manually) to the security settings of both the source and destination databases to allow access. For more information, see Add the IP address whitelist of DTS servers.
- If the source or destination is a self-managed database (i.e., the Access Method is not Alibaba Cloud Instance), you must also click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

Configure the task objects.

On the Configure Objects page, specify the objects to synchronize.

Parameter	Description
Synchronization Types	By default, Incremental Data Synchronization is selected, which supports only Full Data Synchronization. Schema Synchronization is not supported. After the precheck is complete, DTS initializes the synchronization objects in the destination cluster with data from the source instance. This initial data serves as the baseline for subsequent incremental synchronization.
DDL and DML Operations to Be Synchronized	Select the incremental operations to be synchronized at the instance level. Note To select incremental operations at the collection level, right-click the synchronization object in the Selected Objects section and select the desired operations in the dialog box that appears.
Processing Mode of Conflicting Tables	Precheck and Report Errors: Checks for tables with the same names in the destination database. If any tables with the same names are found, an error is reported during the precheck and the data synchronization task does not start. Otherwise, the precheck is successful. Note If you cannot delete or rename the table with the same name in the destination database, you can map it to a different name in the destination. For more information, see Object name mapping. Ignore Errors and Proceed: Skips the check for tables with the same name in the destination database. Warning Selecting Ignore Errors and Proceed may cause data inconsistency and put your business at risk. For example: If the table schemas are consistent and a record in the destination database has the same primary key or unique key value as a record in the source database: During full data synchronization, DTS retains the destination record and skips the source record. During incremental synchronization, DTS overwrites the destination record with the source record. If the table schemas are inconsistent, data initialization may fail. This can result in only partial data synchronization or a complete synchronization failure. Use with caution.
Source Objects	In the Source Objects box, click the objects, and then click to move them to the Selected Objects box. Note You can select objects to be synchronized at the collection level.
Selected Objects	Edit the database name mapping. In the Selected Objects box, right-click the source database that contains the collections to be synchronized. Change Database Name to the name of the schema that receives data in the target AnalyticDB for PostgreSQL instance. In the Edit Database dialog box that appears, modify Database Name (the name of the target schema). Optional: In the Select DDL and DML Operations to Be Synchronized section, select the DML operations to synchronize: insert, update, and delete. Click OK. Edit the table name mapping. In the Selected Objects box, right-click a collection to be synchronized. The Selected Objects panel displays objects in a tree structure. The levels are: Destination Database Name (for example, dtstest) > Table > Specific Table Name (for example, class). Right-click the destination table to perform subsequent operations. Change Table Name to the name of the table that receives data in the target AnalyticDB for PostgreSQL instance. In the Edit Table dialog box that appears, modify Table Name (for example, `class`). After you edit the table or column names, the table and column names in the target database are changed to the new names. Optional: Specify filter conditions. For more information, see Set filter conditions. In the Filter Conditions text box, you can enter MongoDB filter conditions. The syntax is different from the standard SQL WHERE clause. Example: `{"_id": {$gt:"user100844658590795**",$lte:"user101674868045948"}}`, where `$gt` means "greater than" and `$lte` means "less than or equal to". Optional: In the Select DDL and DML Operations to Be Synchronized section, select insert, update, and delete. Configure the fields to be synchronized from the MongoDB database. By default, DTS maps the data of a collection to be synchronized and configures an expression in the Parameter Value column. You must check whether the expression meets your requirements and configure parameters such as Column Name, Type, Length, and Precision. In the `bson_value()` expression of the Parameter Value column, view the name of the corresponding field in the MongoDB database. The field name within the quotation marks (`""`) is the field name in MongoDB. For example, if the expression is `bson_value("age")`, this row corresponds to the `age` field in MongoDB. Optional: Delete fields that do not need to be synchronized. Note To delete a field that does not need to be synchronized, click the icon at the end of the row for that field. Configure the fields to be synchronized. Perform one of the following procedures based on whether the `bson_value()` expression meets your requirements. Correct expression Enter a Column Name. Note This is the name of the column that will receive the data in the destination AnalyticDB for PostgreSQL instance. Select a data Type for the column. Important Make sure that the data types in the destination table are compatible with the data from the source MongoDB database. Optional: Specify a Length and a Precision for the column data. Repeat the preceding steps to map each required field. Incorrect expression Note For example, fields with hierarchical relationships such as parent-child structures. In the Operation column, click the icon at the end of the row for that field. Click + Add Column. In the Additional Columns section, click + Add Column in the upper-right corner. Configure the Column Name, Type, Length, and Precision parameters. In the text box under Parameter Value, enter a `bson_value()` expression. For more information, see Value configuration examples. Important** You must assign `bson_value("_id")` to the primary key column of the destination table. When you configure a `bson_value()` expression, you must specify the path down to the smallest subfield based on the hierarchy. Otherwise, data loss or task failure may occur. Repeat the preceding steps to map each required field. Click OK.

Click Next: Advanced Settings.

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS uses a shared cluster for tasks, so you do not need to make a selection. For greater task stability, you can purchase a dedicated cluster to run the DTS synchronization task. For more information, see What is a DTS dedicated cluster?.
Retry Time for Failed Connections	If the connection to the source or destination database fails after the synchronization task starts, DTS reports an error and immediately begins to retry the connection. The default retry duration is 720 minutes. You can customize the retry time to a value from 10 to 1,440 minutes. We recommend a duration of 30 minutes or more. If the connection is restored within this period, the task resumes automatically. Otherwise, the task fails. Note If multiple DTS instances (e.g., Instance A and B) share a source or destination, DTS uses the shortest configured retry duration (e.g., 30 minutes for A, 60 for B, so 30 minutes is used) for all instances. DTS charges for task runtime during connection retries. Set a custom duration based on your business needs, or release the DTS instance promptly after you release the source/destination instances.
Retry Time for Other Issues	If a non-connection issue (e.g., a DDL or DML execution error) occurs, DTS reports an error and immediately retries the operation. The default retry duration is 10 minutes. You can also customize the retry time to a value from 1 to 1,440 minutes. We recommend a duration of 10 minutes or more. If the related operations succeed within the set retry time, the synchronization task automatically resumes. Otherwise, the task fails. Important The value of Retry Time for Other Issues must be less than that of Retry Time for Failed Connections.
Enable Throttling for Full Data Synchronization	During full data synchronization, DTS consumes read and write resources from the source and destination databases, which can increase their load. To mitigate pressure on the destination database, you can limit the migration rate by setting Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s). Note This parameter is available only if Synchronization Types is set to Full Data Synchronization. You can also adjust the rate of full data synchronization when the synchronization instance is running.
Only one data type for primary key _id in a table of the data to be synchronized	Specify whether the data types of the `_id` primary key are unique within each collection to be synchronized. Important Select an option based on your actual data. An incorrect selection may lead to data loss. This parameter is available only if Synchronization Types includes Full Data Synchronization. Yes: The data types are unique. During the full synchronization phase, DTS does not scan the data types of the primary keys in the source data. For each collection, DTS synchronizes only the data corresponding to one primary key data type. No: The data types are not unique. During the full synchronization phase, DTS scans the data types of the primary keys in the source data and synchronizes all the data.
Enable Throttling for Incremental Data Synchronization	You can also limit the incremental synchronization rate to reduce pressure on the destination database by setting RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s).
Environment Tag	You can select an environment tag to identify the instance based on your business needs. In this example, no tag is needed.
Configure ETL	Choose whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: Enables the ETL feature. Enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: Disables the ETL feature.
Monitoring and Alerting	Choose whether to set up alerts. If the synchronization fails or the latency exceeds the specified threshold, DTS sends a notification to the alert contacts. No: No alerts are configured. Yes: Configures alerts. You must also set the alert threshold and alert contact. For more information, see Configure monitoring and alerting during task configuration.

Save the task and perform a precheck.
- To view the parameters for configuring this instance via an API operation, hover over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the tooltip.
- If you have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.
Note
- Before a synchronization task starts, DTS performs a precheck. You can start the task only if the precheck passes.
- If the precheck fails, click View Details next to the failed item, fix the issue as prompted, and then rerun the precheck.
- If the precheck generates warnings:
  For non-ignorable warning, click View Details next to the item, fix the issue as prompted, and run the precheck again.
  For ignorable warnings, you can bypass them by clicking Confirm Alert Details, then Ignore, and then OK. Finally, click Precheck Again to skip the warning and run the precheck again. Ignoring precheck warnings may lead to data inconsistencies and other business risks. Proceed with caution.

Purchase the instance.

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

On the Purchase page, select the billing method and link specifications for the data synchronization instance. For more information, see the following table.

Category	Parameter	Description
New Instance Class	Billing Method	Subscription: You pay upfront for a specific duration. This is cost-effective for long-term, continuous tasks. Pay-as-you-go: You are billed hourly for actual usage. This is ideal for short-term or test tasks, as you can release the instance at any time to save costs.
	Resource Group Settings	The resource group to which the instance belongs. The default is default resource group. For more information, see What is Resource Management?.
	Instance Class	DTS offers synchronization specifications at different performance levels that affect the synchronization rate. Select a specification based on your business requirements. For more information, see Data synchronization link specifications.
	Subscription Duration	In subscription mode, select the duration and quantity of the instance. Monthly options range from 1 to 9 months. Yearly options include 1, 2, 3, or 5 years. Note This option appears only when the billing method is Subscription.

Read and select the checkbox for Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start, and then click OK in the OK dialog box.
You can monitor the task progress on the data synchronization page.

Value assignment example

Source MongoDB data structure

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

Destination AnalyticDB for PostgreSQL table schema

Name	Type
mongo_id	varchar Note Primary key column.
person_name	varchar
person_age	decimal

Column configuration

Important

Configure the bson_value() expression according to the data hierarchy to prevent data loss or task failure. For example, if you configure the expression as bson_value("person"), Data Transmission Service (DTS) cannot write incremental changes from the sub-fields of the source person object, such as name, age, and sex, to the destination.

Name	Type	Value
mongo_id	STRING	bson_value("_id")
person_name	STRING	bson_value("person","name")
person_age	DECIMAL	bson_value("person","age")