How do I migrate data from a self-managed PostgreSQL database to an ApsaraDB RDS for PostgreSQL instance? - Data Transmission Service

This topic describes how to migrate data from a self-managed PostgreSQL database to an ApsaraDB RDS for PostgreSQL instance by using Data Transmission Service (DTS). DTS supports schema migration, full data migration, and incremental data migration. When you migrate data from a self-managed PostgreSQL database to Alibaba Cloud, you can select all the supported migration types to ensure service continuity.

Prerequisites

The destination ApsaraDB RDS for PostgreSQL instance is created. The available storage space of the destination ApsaraDB RDS for PostgreSQL instance is larger than the total size of the data in the self-managed PostgreSQL database. For more information about how to create the destination ApsaraDB RDS for PostgreSQLL instance, see Create an ApsaraDB RDS for PostgreSQL instance. For more information about the supported database versions, see Overview of data migration scenarios.
Note
To ensure compatibility, the version of the destination database must be the same as or later than that of the source database.
If the version of the destination database is earlier than that of the source database, database compatibility issues may occur.
A database is created in the destination ApsaraDB RDS for PostgreSQL instance to receive data. For more information, see Create a database.

Limits

Category	Description
Limits on the source database	The server on which the source database resides must have sufficient outbound bandwidth. Otherwise, the data migration speed is affected. The tables to be migrated must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records. The name of the source database cannot contain hyphens (-). Example: dts-testdata. If you select tables as the objects to be migrated and you need to edit tables, such as renaming tables or columns in the destination database, up to 1,000 tables can be migrated in a single data migration task. If you run a task to migrate more than 1,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to migrate the tables or configure a task to migrate the entire database. DTS cannot migrate temporary tables in the source database, internal triggers, or some internal procedures and functions written in the C programming language. DTS can migrate custom parameters of the COMPOSITE, ENUM, and RANGE types. The tables to be migrated must have the PRIMARY KEY, FOREIGN KEY, UNIQUE, or CHECK constraints. If you need to migrate incremental data, you must make sure that the following requirements are met: The value of the wal_level parameter must be set to logical. For an incremental data migration, the WAL logs of the source database must be stored for more than 24 hours. For a full data and incremental data migration, the WAL logs of the source database must be stored for at least seven days. Otherwise, DTS may fail to obtain the WAL logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. After full data migration is complete, you can set the retention period to more than 24 hours. Make sure that you set the retention period of WAL logs based on the preceding requirements. Otherwise, the service reliability or performance in the Service Level Agreement (SLA) of DTS may not be guaranteed. Limits on operations to be performed on the source database: If you perform a primary/secondary switchover on the source self-managed PostgreSQL database, the data migration task fails. During schema migration and full data migration, do not perform DDL operations to change the schemas of databases or tables. Otherwise, the data migration task fails. If the source database has one or more long-running transactions and incremental data is migrated in the data migration task, the WAL logs that are generated before the long-running transactions are committed may not be cleared and therefore pile up, resulting in insufficient storage space in the source database.
Other limits	Data may be inconsistent between the primary and secondary nodes of the source database due to migration latency. Therefore, you must use the primary node as the data source when you migrate data. A single data migration task can migrate data from only one database. To migrate data from multiple databases, you must create a data migration task for each database. If you select a schema as the object to be migrated and create a table in the schema or execute the RENAME statement to rename a table in the schema during incremental data migration, you must execute the `ALTER TABLE schema.table REPLICA IDENTITY FULL;` statement before you write data to the table. Note Replace the `schema` and `table` in the preceding sample statement with the actual schema name and table name. DTS does not check the validity of metadata such as sequences. You must manually check the validity of metadata. After your workloads are switched to the destination database, newly written sequences do not increment from the maximum value of the sequences in the source database. Therefore, you must query the maximum value of the sequences in the source database before you switch your workloads to the destination database. Then, you must specify the queried maximum value as the initial value of the sequences in the destination database. You can execute the following statements to query the maximum value of the sequences in the source database: `do language plpgsql $$ declare nsp name; rel name; val int8; begin for nsp,rel in select nspname,relname from pg_class t2 , pg_namespace t3 where t2.relnamespace=t3.oid and t2.relkind='S' loop execute format($_$select last_value from %I.%I$_$, nsp, rel) into val; raise notice '%', format($_$select setval('%I.%I'::regclass, %s);$_$, nsp, rel, val+1); end loop; end; $$;` DTS creates the following temporary tables in the source database to obtain the DDL statements of incremental data, the schemas of incremental tables, and the heartbeat information. During data migration, do not delete temporary tables in the source database. Otherwise, exceptions occur. After the DTS instance is released, temporary tables are automatically deleted. `public.dts_pg_class`, `public.dts_pg_attribute`, `public.dts_pg_type`, `public.dts_pg_enum`, `public.dts_postgres_heartbeat`, `public.dts_ddl_command`, and `public.dts_args_session`. To ensure that the latency of incremental data migration is accurate, DTS creates a heartbeat table named `dts_postgres_heartbeat` in the source database. During incremental data migration, DTS creates a replication slot for the source database. The replication slot is prefixed with `dts_sync_`. By using this replication slot, DTS can obtain the incremental logs of the source database within the last 15 minutes. Note If the data migration task is released or fails, DTS automatically clears the replication slot. If a primary/secondary switchover is performed on the source ApsaraDB for PostgreSQL instance, you must log on to the secondary instance to clear the replication slot. If you run a full or incremental data migration task, the tables to be migrated from the source database contain foreign keys, triggers, or event triggers, and the account of the destination database is a privileged account or an account that has the permissions of the superuser role, DTS temporarily sets the session_replication_role parameter to replica at the session level during full or incremental data migration. If the account of the destination database does not have the permissions, you must manually set the session_replication_role parameter to replica in the destination database. After the session_replication_role parameter is set to replica during full migration or incremental migration, if a cascade update or delete operation is performed in the source database, data inconsistency may occur. After the DTS migration task is released, you can change the value of the session_replication_role parameter to origin. Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data migration is complete, the tablespace of the destination database is larger than that of the source database. Make sure that the precision settings for columns of the FLOAT or DOUBLE data type meet your business requirements. DTS uses the `ROUND(COLUMN,PRECISION)` function to retrieve values from columns of the FLOAT or DOUBLE data type. If you do not specify a precision, DTS sets the precision for the FLOAT data type to 38 digits and the precision for the DOUBLE data type to 308 digits. DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch workloads to the destination database, you must stop or release the failed tasks. You can also execute the `REVOKE` statement to revoke the write permissions from the accounts that are used by DTS to access the destination database. Otherwise, the data in the source database will overwrite the data in the destination database after the failed task is resumed.

Migration types

Schema migration
DTS migrates the schemas of objects from the source database to the destination database.
Note
DTS supports schema migration for the following types of objects: table, trigger, view, sequence, function, user-defined type, rule, domain, operation, and aggregate.
Full data migration
DTS migrates the existing data of objects from the source database to the destination database.
Incremental data migration
After full data migration is complete, DTS migrates incremental data from the source database to the destination database. Incremental data migration allows data to be migrated smoothly without interrupting the services of self-managed applications during data migration.

SQL operations that can be incrementally migrated

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE
DDL	DDL operations can be migrated only in the data migration tasks that are created after October 1, 2020. Important To run a data migration task created before May 12, 2023 to migrate DDL operations, you must create a trigger and a function in the source database to capture DDL information before you configure the data migration task. For more information, see Use triggers and functions to implement incremental DDL migration for PostgreSQL databases. Incremental data migration does not support data of the BIT type. The database account of the source database must be a privileged account. DTS supports the following DDL statements in data migration tasks: CREATE TABLE and DROP TABLE ALTER TABLE, including RENAME TABLE, ADD COLUMN, ADD COLUMN DEFAULT, ALTER COLUMN TYPE, DROP COLUMN, ADD CONSTRAINT, ADD CONSTRAINT CHECK, and ALTER COLUMN DROP DEFAULT TRUNCATE TABLE (The database engine version of the source PostgreSQL database must be PostgreSQL 11 or later.) CREATE INDEX ON TABLE Important You cannot migrate additional information of DDL statements, such as CASCADE or RESTRICT. You cannot migrate the DDL statements from a session in which the `SET session_replication_role = replica` statement is executed. If the SQL statements submitted by the source database at a time contain both DML and DDL statements, DTS does not migrate the DDL statements. If the SQL statements submitted by the source database at a time contain DDL statements that are not to be migrated, DTS does not migrate the DDL statements. The CREATE SEQUENCE statement is not supported.

Permissions required for database accounts

Database	Schema migration	Full data migration	Incremental data migration
Self-managed PostgreSQL database	The USAGE permission on pg_catalog.	The SELECT permission on the objects to be migrated.	The permissions of the superuser role.
ApsaraDB RDS for PostgreSQL instance	The CREATE and USAGE permissions on the objects to be migrated	Permissions of the schema owner.	Permissions of the schema owner.

For more information about how to create a database account and grant permissions to the account, see the following topics.

Self-managed PostgreSQL database: CREATE USER and GRANT
ApsaraDB RDS for PostgreSQL instance: Create an account

Before you begin

Note

For more information about how to make preparations if your source database is an Amazon RDS for PostgreSQL instance, see the Before you begin section of the "Migrate incremental data from an Amazon RDS for PostgreSQL instance to an ApsaraDB RDS for PostgreSQL instance" topic. For more information about how to make preparations if your source database is an Amazon Aurora PostgreSQL instance, see the Preparation 1: Edit the inbound rule of the Amazon Aurora PostgreSQL instance section of the "Migrate full data from an Amazon Aurora PostgreSQL instance to an ApsaraDB RDS for PostgreSQL instance" topic.
In this example, a self-managed PostgreSQL database that runs on a Linux server is used.

Perform the following operations before you configure a data migration task:

Log on to the server on which the self-managed PostgreSQL database resides.
Run the following command to query the number of used replication slots in the self-managed PostgreSQL database:
```
select count(1) from pg_replication_slots;
```

Modify the postgresql.conf configuration file. Set the wal_level parameter to logical, and make sure that the values of the max_wal_senders and max_replication_slots parameters are greater than the sum of the number of used replication slots in the self-managed PostgreSQL database and the number of DTS instances whose source database is the self-managed PostgreSQL database.

# - Settings -

wal_level = logical			# minimal, replica, or logical
					# (change requires restart)

......

# - Sending Server(s) -

# Set these on the master and on any standby that will send replication data.

max_wal_senders = 10		# max number of walsender processes
				# (change requires restart)
#wal_keep_segments = 0		# in logfile segments, 16MB each; 0 disables
#wal_sender_timeout = 60s	# in milliseconds; 0 disables

max_replication_slots = 10	# max number of replication slots
				# (change requires restart)

Note

After you modify the configuration file, restart the self-managed PostgreSQL database to make the parameter settings take effect.

Add the CIDR blocks of DTS servers to the pg_hba.conf configuration file of the self-managed PostgreSQL database. Add only the CIDR blocks of the DTS servers that reside in the same region as the destination database. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.
Note
- After you modify the configuration file, execute the SELECT pg_reload_conf(); statement or restart the self-managed PostgreSQL database to make the parameter settings take effect.
- For more information about the pg_hba.conf configuration file, see The pg_hba.conf File. Skip this step if you have set the IP address in the pg_hba.conf file to 0.0.0.0/0. The following figure shows the configurations.
Create a database and schema in the destination ApsaraDB RDS for PostgreSQL instance based on the database and schema information of the objects to be migrated. The schema name in the source and destination databases must be the same. For more information, see Create a database and Manage accounts by using schemas.

If the version of the self-managed PostgreSQL database is in the range of 9.4.8 to 10.0, you must perform the following operations before you configure a data migration task:

Download the PostgreSQL source code from the official website, compile the source code, and install PostgreSQL.
1. Download the source code from the PostgreSQL official website based on the version of the self-managed PostgreSQL database.
2. Run the sudo ./configure, sudo make, and sudo make install commands in sequence to configure and compile the source code, and install PostgreSQL.
  Important
  When you compile the source code and install PostgreSQL, the operating system version of PostgreSQL must be consistent with the GNU Compiler Collection (GCC) version.
  If an error occurs when you run the sudo ./configure command, you can modify the command based on the error message. For example, if the error message is readline library not found. Use --without-readline to disable readline support., you can modify the command to sudo ./configure --without-readline.
  If you use another method to install PostgreSQL, you must compile the ali_decoding plug-in in a test environment that has the same operating system version and GCC version.

Download the ali_decoding plug-in provided by DTS, and compile and install the plug-in.

Download ali_decoding.
Copy the ali_decoding directory to the contrib directory of PostgreSQL that is compiled and installed.

Go to the ali_decoding directory and replace the content of the Makefile file with the following script:

# contrib/ali_decoding/Makefile
MODULE_big = ali_decoding
MODULES = ali_decoding
OBJS    = ali_decoding.o

DATA = ali_decoding--0.0.1.sql ali_decoding--unpackaged--0.0.1.sql

EXTENSION = ali_decoding

NAME = ali_decoding

#subdir = contrib/ali_decoding
#top_builddir = ../..
#include $(top_builddir)/src/Makefile.global
#include $(top_srcdir)/contrib/contrib-global.mk

#PG_CONFIG = /usr/pgsql-9.6/bin/pg_config
#pgsql_lib_dir := $(shell $(PG_CONFIG) --libdir)
#PGXS := $(shell $(PG_CONFIG) --pgxs)
#include $(PGXS)

# Run the following commands to install the ali_decoding plug-in:
ifdef USE_PGXS
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
else
subdir = contrib/ali_decoding
top_builddir = ../..
include $(top_builddir)/src/Makefile.global
include $(top_srcdir)/contrib/contrib-global.mk
endif

Go to the ali_decoding directory, and run the sudo make and sudo make install commands in sequence to compile the ali_decoding plug-in and obtain the files that are required to install the ali_decoding plug-in.
Copy the files to the specified directories.

Create a database and schema in the destination ApsaraDB RDS for PostgreSQL instance based on the database and schema information of the objects to be migrated. The schema name in the source and destination databases must be the same. For more information, see Create a database and Manage accounts by using schemas.

Procedure

Go to the Data Migration Tasks page.
1. Log on to the Data Management (DMS) console.
2. In the top navigation bar, click DTS.
3. In the left-side navigation pane, choose DTS (DTS) > Data Migration.
Note
- 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.
- You can also go to the Data Migration Tasks page of the new DTS console.
From the drop-down list next to Data Migration Tasks, select the region in which the data migration instance resides.
Note If you use the new DTS console, you must select the region in which the data migration instance resides in the upper-left corner.

Click Create Task. On the Create Task page, configure the source and destination databases.

Section	Parameter	Description
N/A	Task Name	The name of the task. DTS automatically assigns a name to the task. 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 an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the database.
	Database Type	The type of the source database. Select PostgreSQL.
	Access Method	The access method of the source database. Select a value based on the deployment of the source database. In this example, Cloud Enterprise Network (CEN) is selected. Note If your source database is a self-managed database, you must deploy the network environment for the database. For more information, see Preparation overview.
	Instance Region	The region in which the self-managed PostgreSQL database resides.
	CEN instance ID	The ID of the CEN instance that hosts the self-managed PostgreSQL database.
	Connected VPC	The virtual private cloud (VPC) in which the self-managed PostgreSQL database is deployed.
	IP Address or Domain Name	The IP address of the server on which the self-managed PostgreSQL database resides.
	Port Number	The service port number of the self-managed PostgreSQL database. Default value: 5432.
	Database Name	The name of the self-managed PostgreSQL database from which you want to migrate objects.
	Database Account	The database account of the self-managed PostgreSQL database. For more information about the permissions required for the database account, see the Permissions required for database accounts section of this topic.
	Database Password	The password of the database account.
Destination Database	Select an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the database.
	Database Type	The type of the destination database. Select PostgreSQL.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination ApsaraDB RDS for PostgreSQL instance resides.
	Instance ID	The ID of the destination ApsaraDB RDS for PostgreSQL instance.
	Database Account	The name of the database that receives the migrated objects in the destination ApsaraDB RDS for PostgreSQL instance.
	Database Account	The database account of the destination ApsaraDB RDS for PostgreSQL instance. For more information about the permissions required for the database account, see the Permissions required for database accounts section of this topic.
	Database Password	The password of the database account.

In the lower part of the page, click Test Connectivity and Proceed.
If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the IP address whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance, and you must make sure that the ECS instance can access the database. If the self-managed database is hosted on multiple ECS instances, you must manually add the CIDR blocks of DTS servers to the security group rules of each ECS instance. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the IP address whitelist of the database to allow DTS to access the database. For more information, see the "CIDR blocks of DTS servers" section of the Add the CIDR blocks of DTS servers to the security settings of on-premises databases topic.
Warning
If the public CIDR blocks of DTS servers are automatically or manually added to the IP address whitelist of a database instance or to the security group rules of an ECS instance, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your account and password, limiting the ports that are exposed, authenticating API calls, regularly checking the IP address whitelist or ECS security group rules and forbidding unauthorized CIDR blocks, and connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

Configure the objects to be migrated and the advanced settings.

Parameter	Description
Migration Types	To perform only full data migration, select Schema Migration and Full Data Migration. To ensure service continuity during data migration, select Schema Migration, Full Data Migration, and Incremental Data Migration. Note If you select Schema Migration, DTS migrates the schemas (including foreign keys) of the tables to be migrated from the source database to the destination database. If Incremental Data Migration is not selected, we recommend that you do not write data to the source database during data migration. This ensures data consistency between the source and destination databases.
Processing Mode of Conflicting Tables	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 migration task cannot be started. Note You can use the object name mapping feature to rename the tables that are migrated to the destination database. You can use this feature if the source and destination databases contain tables that have identical table names and the tables in the destination database cannot be deleted or renamed. 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 the following potential risks: If the source and destination databases have the same schemas, DTS does not migrate data records that have the same primary key values as data records in the destination database. If the source and destination databases have different schemas, only specific columns are migrated or the data migration task fails. Proceed with caution.
Capitalization of Object Names in Destination Instance	The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to make sure that the capitalization of object names is consistent with that 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. Click the icon to add the objects to the Selected Objects section. Note You can select columns, tables, or schemas as the objects to be migrated. If you select tables or columns as the objects to be migrated, DTS does not migrate other objects, such as views, triggers, or stored procedures, to the destination database.
Selected Objects	To rename an object that you want to migrate to the destination instance, right-click the object in the Selected Objects section. For more information, see the Map the name of a single object section of the "Map object names" topic. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see the Map multiple object names at a time section of the "Map object names" topic. Note If you use the object name mapping feature to rename an object, other objects that depend on the object may fail to be migrated. To specify WHERE conditions to filter data, right-click an object in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Set filter conditions. To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to migrate. For more information, see the SQL operations that can be incrementally migrated section of this topic.

Click Next: Advanced Settings to configure advanced settings.

Data Verification Settings
For more information about how to use the data verification feature, see Enable data verification.

Advanced Settings

Parameter	Description
Select the dedicated cluster used to schedule the task	By default, DTS schedules the data migration task to the shared cluster if you do not specify a dedicated cluster. You can also purchase and specify a dedicated cluster of the required specifications to run the data migration task. For more information, see What is a DTS dedicated cluster.
Set Alerts	Specifies whether to configure alerting for the data migration task. If the task fails or the migration latency exceeds the specified threshold, the alert contacts will receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. If you select Yes, you must also specify the alert threshold and alert contacts. For more information, see Configure monitoring and alerting.
Retry Time for Failed Connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data migration task is started, DTS immediately retries a connection within the retry time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS is reconnected to the source and destination databases within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you specify different retry time ranges for multiple data migration tasks that share the same source or destination database, the value that is specified later takes precedence. When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
The wait time before a retry when other issues occur in the source and destination databases.	The retry time range for other issues. For example, if DDL or DML operations fail to be performed after the data migration task is started, DTS immediately retries the operations within the retry time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set the parameter to a value greater than 10. If the failed operations are successfully performed within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Important The value of the The wait time before a retry when other issues occur in the source and destination databases parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Full Data Migration	Specifies whether to enable throttling for full data migration. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. You can enable throttling for full data migration based on your business requirements. To configure throttling, you must configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters. This reduces the loads of the destination database server. Note This parameter is displayed only when Full Data Migration is selected as Migration Types.
Enable Throttling for Incremental Data Migration	Specifies whether to enable throttling for incremental data migration. To configure throttling, you must configure the RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) parameters. This reduces the loads of the destination database server. Note This parameter is displayed only when Incremental Data Migration is selected as Migration Types.
Environment Tag	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements. In this example, you do not need to configure this parameter.
Configure ETL	Specifies whether to configure 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 synchronization task. No: does not configure the ETL feature.

In the lower part of the page, click Next: Save Task Settings and Precheck.
You can move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters to view the parameters to be specified when you call the relevant API operation to configure the DTS task.
Note
- Before you can start the data migration task, DTS performs a precheck. You can start the data migration task only after the task passes the precheck.
- If the task fails to pass the precheck, click View Details next to each failed item. After you troubleshoot the issues based on the error message, you can run a precheck again.
- If an alert is triggered for an item during the precheck:
  If the alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issues. Then, run a precheck again.
  If the alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur and your business may be exposed to potential risks.
Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.

On the Purchase Instance page, configure the Instance Class parameter for the data migration instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Resource Group	The resource group to which the data migration instance belongs. Default value: default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Specifications of data migration instances.

Read and agree to Data Transmission Service (Pay-as-you-go) Service Terms by selecting the check box.
Click Buy and Start to start the data migration task. You can view the progress of the task in the task list.