Incremental migration: Amazon RDS for PostgreSQL to Alibaba Cloud - ApsaraDB RDS

This topic describes how to migrate data from an Amazon RDS for PostgreSQL instance to an ApsaraDB RDS for PostgreSQL instance using DTS. DTS supports schema migration, full data migration, and incremental data migration. Combining these migration types allows you to migrate your database without interrupting your self-managed applications.

Prerequisites

The Amazon RDS for PostgreSQL instance must be version 10.4 or later.
To allow DTS to connect to the Amazon RDS for PostgreSQL instance over the internet, set Publicly accessible to Yes.
To allow DTS to read incremental data from the Amazon RDS for PostgreSQL instance, set the rds.logical_replication parameter to 1 in the parameter group.
You must have an ApsaraDB RDS for PostgreSQL instance. For more information, see Create an ApsaraDB RDS for PostgreSQL instance.
Note
- We recommend that the major version of the ApsaraDB RDS for PostgreSQL instance is the same as that of the Amazon RDS for PostgreSQL instance. To migrate data between different major versions, create a pay-as-you-go instance to verify compatibility.
- The ApsaraDB RDS for PostgreSQL instance must have more available storage space than the storage space used by the database on the Amazon RDS for PostgreSQL instance.

Considerations

During a full data migration, DTS consumes read and write resources on the source and destination databases, increasing their load. If your databases have poor performance, low specifications, or high workloads (for example, if the source database has many slow SQL queries or tables without primary keys, or if deadlocks occur in the destination database), the increased load can strain your databases or even cause service interruptions. Perform the data migration during off-peak hours, such as when the CPU utilization of both databases is below 30%.
If a table being migrated lacks a primary key or unique constraint, duplicate data might be created in the destination database, causing the migration to fail.
A data migration task can migrate only one database. To migrate multiple databases, you must create a separate data migration task for each.
Only DML operations (INSERT, DELETE, and UPDATE) are supported.
During data migration, DTS creates a replication slot in Amazon RDS for PostgreSQL. This replication slot is prefixed with dts_sync_. To prevent the replication slot from consuming excessive disk space, DTS automatically cleans up historical replication slots every 90 minutes.

Note
DTS automatically cleans up the replication slot if the data migration task is released or fails. If a primary/secondary switchover occurs on the Amazon RDS for PostgreSQL instance, you must manually log on to the secondary database to clean up the slot.

You can run the SELECT * FROM pg_replication_slots; command in a PostgreSQL client to query information about replication slots. Verify that the logical replication slot created by DTS with the prefix dts_sync_ and a slot_type of logical is active (its active column is true).
A primary/secondary switchover on the Amazon RDS for PostgreSQL instance causes the DTS task to fail, and it may not be resumable.
If a data migration task fails, DTS automatically triggers recovery. Before you switch your workloads to the destination instance, you must stop or release the task. Otherwise, if the task is automatically recovered, source data may overwrite data in the destination instance.

Billing

Migration type	Task configuration fee	Internet traffic fee
Schema migration and full data migration	Free of charge.	DTS charges an Internet traffic fee when the Access Method of the destination database is set to Public IP Address. Billing overview.
Incremental data migration	Charged. Billing overview.

Migration types

Schema migration

DTS migrates the schemas of the following object types to an ApsaraDB RDS for PostgreSQL instance: table, trigger, view, sequence, function, user-defined type, rule, domain, operation, and aggregate.

Note
DTS does not support migrating functions written in the C programming language.
Full data migration

DTS migrates all data from specified objects to the destination ApsaraDB RDS for PostgreSQL instance.
Incremental data migration

After a full data migration, DTS migrates incremental updates to the ApsaraDB RDS for PostgreSQL instance, which enables a seamless migration without application downtime.

Database account permissions

Database	Schema migration	Full data migration	Incremental data migration
Amazon RDS for PostgreSQL	USAGE permission on the pg_catalog schema	SELECT permission on the objects to migrate	rds_superuser permission
ApsaraDB RDS for PostgreSQL	CREATE and USAGE permissions on the objects to migrate	Schema owner permissions	Schema owner permissions

Data migration process

To resolve object dependencies and improve the migration success rate, DTS migrates the PostgreSQL schema and data in the following order:

Schema migration for tables, views, sequences, functions, user-defined types, rules, domains, operations, and aggregates.
Full data migration.
Schema migration for triggers and foreign keys.
Incremental data migration.

Note
Do not perform DDL operations on migration objects in the Amazon RDS for PostgreSQL instance before the incremental data migration. Doing so can cause the migration to fail.

Before you begin

Log on to the Amazon RDS Management Console.
In the upper-right corner of the page, select the region of your destination instance.
In the left-side navigation pane, click Database. Then, click the destination database's identifier to view the Basic Information page.
In the Security group rules section, click the security group name of the inbound rule.
On the Security group settings page, add the IP addresses of the DTS servers for the target region to the inbound rules. For details about the IP address ranges, see Add IP addresses of DTS servers to the IP allowlist of an on-premises database.
Click the Inbound rules tab, and then click Edit inbound rules. In the Edit inbound rules dialog box, set Type to custom TCP rule and Port range to 5432. For Source, select Custom and enter the IP addresses of the corresponding DTS servers. Click Save rules.
Note
- Add only the CIDR blocks for DTS servers in the destination database's region. For example, if your source database is in the Singapore region and your destination database is in the China (Hangzhou) region, you only need to add the CIDR blocks for DTS servers in the China (Hangzhou) region.
- You can add multiple CIDR blocks to a single rule.
- For more information, see the official AWS documentation or contact AWS Support.

Procedure (new console)

Navigate to the migration task list page for the destination region using one of the following methods.
From the DTS console
1. Log on to the Data Transmission Service (DTS) console.
2. In the navigation pane on the left, click Data Migration.
3. In the upper-left corner of the page, select the region where the migration instance is located.
From the DMS console

Note
The actual operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode console and Customize the layout and style of the DMS console.
1. Log on to the Data Management (DMS) console.
2. In the top menu bar, choose Data + AI > Data Transmission (DTS) > Data Migration.
3. To the right of Data Migration Tasks, select the region where the migration instance is located.
Click Create Task to navigate to the task configuration page.

Configure the source and destination databases.

Warning

After you select the source and destination instances, we recommend that you carefully read the limits displayed at the top of the page. Otherwise, the task may fail or data inconsistency may occur.

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 a DMS database instance.	You can choose whether to use an existing instance, as needed. If you use an existing instance, the database information below is automatically filled in. You do not need to enter it again. If you do not use an existing instance, you must configure the database information below. Note In the DMS console, you can click Add DMS Database Instance to register a database with DMS. For more information, see ApsaraDB Data Ingestion and Register a database hosted on a third-party cloud service or a self-managed database. In the DTS console, you can register a database with DTS on the Database Connections page or the new configuration page. For more information, see Manage database connections.
	Database Type	Select PostgreSQL.
	Connection Type	Select Public IP Address.
	Instance Region	Select the region where the Amazon RDS for PostgreSQL database is located. Note If the region of the Amazon RDS for PostgreSQL database is not in the drop-down list, you can select the region that is geographically closest to the database.
	Domain Name or IP	Enter the endpoint of the Amazon RDS for PostgreSQL instance. Note You can find the endpoint on the Basic Information page of your Amazon RDS for PostgreSQL instance.
	Port Number	Enter the service port of the Amazon RDS for PostgreSQL instance. The default value is 5432.
	Database Name	Enter the name of the database on the Amazon RDS for PostgreSQL instance that you want to migrate.
	Database Account	Enter the database account of the Amazon RDS for PostgreSQL instance. For information about the required permissions, see Database account permissions.
	Database Password	Enter the password for the database account.
	Encryption	Select a connection method. In this example, Non-encrypted is selected. If you need to connect to the database by using SSL encryption, select SSL-encrypted, and then upload the CA Certificate, Client Certificate, and Private Key of Client Certificate as needed. Then, enter the Private Key Password of Client Certificate. Note If you select SSL-encrypted for a self-managed PostgreSQL database, you must upload the CA Certificate. If you need to use a client certificate, you must upload both the Client Certificate and the Private Key of Client Certificate, and then enter the Private Key Password of Client Certificate. For information about the SSL encryption feature for an RDS for PostgreSQL instance, see SSL connection encryption.
Destination Database	Select a DMS database instance.	You can choose whether to use an existing instance, as needed. If you use an existing instance, the database information below is automatically filled in. You do not need to enter it again. If you do not use an existing instance, you must configure the database information below. Note In the DMS console, you can click Add DMS Database Instance to register a database with DMS. For more information, see ApsaraDB Data Ingestion and Register a database hosted on a third-party cloud service or a self-managed database. In the DTS console, you can register a database with DTS on the Database Connections page or the new configuration page. For more information, see Manage database connections.
	Database Type	Select PostgreSQL.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination ApsaraDB RDS for PostgreSQL instance is located.
	Instance ID	Select the instance ID of the destination ApsaraDB RDS for PostgreSQL instance.
	Database Name	Enter the name of the database in the ApsaraDB RDS for PostgreSQL instance where you want to migrate data. The name can be different from that of the source database. Note Make sure that this database is created in the destination ApsaraDB RDS for PostgreSQL instance. For more information, see Create a database.
	Database Account	Enter the database account of the destination ApsaraDB RDS for PostgreSQL instance. For information about the required permissions, see Database account permissions.
	Database Password	Enter the password for the database account.
	Encryption	Select a connection method. In this example, Non-encrypted is selected. If you need to connect to the database by using SSL encryption, select SSL-encrypted, and then upload the CA Certificate, Client Certificate, and Private Key of Client Certificate as needed. Then, enter the Private Key Password of Client Certificate. Note If you select SSL-encrypted for a self-managed PostgreSQL database, you must upload the CA Certificate. If you need to use a client certificate, you must upload both the Client Certificate and the Private Key of Client Certificate, and then enter the Private Key Password of Client Certificate. For information about the SSL encryption feature for an RDS for PostgreSQL instance, see SSL connection encryption.

After you complete the configuration, click Test Connectivity and Proceed at the bottom of the page. In the CIDR Blocks of DTS Servers dialog box that appears, click Test Connectivity.

Note
Ensure that the IP address segments of the DTS service are 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 DTS server IP addresses to a whitelist.

Configure the task objects.

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

Parameter	Description
Migration Types	Select both Schema Migration and Incremental Data Migration. We recommend that you also select Full Data Migration.
Processing Mode of Conflicting Tables	Precheck and Report Errors: Checks whether tables with the same names exist in the destination database. If no tables with the same names exist, the precheck is passed. If tables with the same names exist, an error is reported during the precheck, and the data migration task does not start. Note If a table in the destination database has the same name but cannot be easily deleted or renamed, you can change the name of the table in the destination database. For more information, see Object name mapping. Ignore Errors and Proceed: Skips the check for tables with the same names. Warning Selecting Ignore Errors and Proceed may cause data inconsistency and business risks. For example: If the table schemas are consistent and a record in the destination database has the same primary key value as a record in the source database: During full migration, DTS keeps the record in the destination database. The record from the source database is not migrated. During incremental migration, DTS does not keep the record in the destination database. The record from the source database overwrites the record in the destination database. If the table schemas are inconsistent, only some columns of data may be migrated, or the migration may fail. Proceed with caution.
Capitalization of Object Names in Destination Instance	You can configure the case sensitivity policy for the names of migrated objects, such as databases, tables, and columns, in the destination instance. By default, DTS default policy is selected. You can also choose to keep the case sensitivity consistent with the default policy of the source or destination database. For more information, see Case sensitivity of object names in the destination database.
Source Objects	Select one or more objects from the Source Objects section. Click the icon and add the objects to the Selected Objects section. Note The granularity for selecting migration objects is schema, table, and column. If you select only tables or columns as migration objects, other objects such as views, triggers, and stored procedures are not migrated to the destination database.
Selected Objects	To change the name of a single migration object in the target instance, right-click the object in the Selected Objects box. For more information, see Map individual schema, table, and column names. To change the names of multiple migration objects in the target instance, click Selected Objects in the upper-right corner of the Batch Edit box. For more information, see Map multiple schema, table, and column names. Note If you use the object name mapping feature, other objects that depend on the renamed object may fail to migrate. To filter data by using WHERE conditions, right-click the table to migrate in the Selected Objects box, and specify the filter conditions in the dialog box that appears. For more information, see Filter data by using SQL conditions. To select the SQL operations to migrate at the database or table level, right-click the object in the Selected Objects box, and select the desired SQL operations in the dialog box that appears.

Click Next: Advanced Settings to configure advanced parameters.

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules tasks on a shared cluster. You do not need to select one. If you want more stable tasks, you can purchase a dedicated cluster to run DTS migration tasks.
Retry Time for Failed Connections	After the migration task starts, if the connection to the source or destination database fails, 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 1440 minutes. We recommend that you set the duration to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified duration, the migration task automatically resumes. Otherwise, the task fails. Note For multiple DTS instances that share the same source or destination, the network retry time is determined by the setting of the last created task. Because you are charged for the task during the connection retry period, we recommend that you customize the retry time based on your business needs, or release the DTS instance as soon as possible after the source and destination database instances are released.
Retry Time for Other Issues	After the migration task starts, if a non-connectivity issue, such as a DDL or DML execution exception, occurs in the source or destination database, DTS reports an error and immediately begins to retry the operation. The default retry duration is 10 minutes. You can customize the retry time to a value from 1 to 1440 minutes. We recommend that you set the duration to more than 10 minutes. If the related operations succeed within the specified retry duration, the migration task automatically resumes. Otherwise, the task fails. Important The value of Retry Time for Other Issues must be less than the value of Retry Time for Failed Connections.
Enable Throttling for Full Data Migration	During full migration, DTS consumes read and write resources on the source and destination databases, which may increase the database load. If required, you can enable throttling for the full migration task. You can set Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) to reduce the load on the destination database. Note This configuration item is available only if you select Full Data Migration for Migration Types. You can also adjust the full migration speed after the migration instance is running.
Enable Throttling for Incremental Data Migration	If required, you can also choose to set speed limits for the incremental migration task. You can set RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) to reduce the load on the destination database. Note This configuration item is available only if you select Incremental Data Migration for Migration Types. You can also adjust the incremental migration speed after the migration instance is running.
Environment Tag	You can select an environment tag to identify the instance based on your requirements. This parameter is optional.
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	Select whether to set alerts and receive alert notifications based on your business needs. No: Does not set an alert. Yes: Configure alerts by setting an alert threshold and an alert notifications. If a migration fails or the latency exceeds the threshold, the system sends an alert notification.

Click Next: Data Validation to configure a data validation task.

For more information about the data validation feature, see Configure data validation.

Save the task and run a precheck.
- To view the parameters for configuring this instance when you call the API operation, move the pointer over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the bubble that appears.
- If you do not need to view or have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.
Note
- Before the migration task starts, DTS performs a precheck. The task starts only after it passes the precheck.
- If the precheck fails, click View Details next to the failed check item, fix the issue based on the prompt, and then run the precheck again.
- If a warning is reported during the precheck:
  
  For check items that cannot be ignored, click View Details next to the failed item, fix the issue based on the prompt, and then run the precheck again.
  
  For check items that can be ignored, you can click Confirm Alert Details, Ignore, OK, and Precheck Again to skip the alert item and run the precheck again. If you choose to ignore a warning, it may cause issues such as data inconsistency and pose risks to your business.

Purchase the instance.

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

On the Purchase page, select the link specification for the data migration instance. For more information, see the following table.

Category	Parameter	Description
New Instance Class	Resource Group Settings	Select the resource group to which the instance belongs. The default value is default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides migration specifications with different performance levels. The link specification affects the migration speed. You can select a specification based on your business scenario. For more information, see Data migration link specifications.

After the configuration is complete, read and select Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start. In the OK dialog box that appears, click OK.

You can view the progress of the migration task on the Data Migration Tasks list page.
Note
- If the migration task does not include incremental migration, it stops automatically after the full migration is complete. After the task stops, its Status changes to Completed.
- If the migration task includes incremental migration, it does not stop automatically. The incremental migration task continues to run. While the incremental migration task is running, the Status of the task is Running.

Procedure (old console)

Log on to the DTS console.

Note
If you are automatically redirected to the Data Management (DMS) console, you can click the icon in the lower-right corner and then click to return to the classic DTS console.
In the left-side navigation pane, click Data Migration.
At the top of the Migration Tasks page, select the region of the destination cluster.
In the upper-right corner of the page, click Create Data Migration Task.