Migrate data between ApsaraDB RDS for SQL Server instances - RDS SQL Server Database| Alibaba Cloud Documentation Center

This topic describes how to use Data Transmission Service (DTS) to migrate data between RDS instances. DTS supports schema migration, full data migration, and incremental data migration. When you configure a data migration task, you can select all of the supported migration types to ensure service continuity.

Prerequisites

The database types of the RDS instances meet the following requirements.


Source database	Destination database
ApsaraDB RDS for MySQL ApsaraDB RDS for MariaDB TX	ApsaraDB RDS for MySQL ApsaraDB RDS for MariaDB TX
ApsaraDB RDS for SQL Server	ApsaraDB RDS for SQL Server
ApsaraDB RDS for PostgreSQL	ApsaraDB RDS for PostgreSQL
ApsaraDB RDS for PPAS	ApsaraDB RDS for PPAS

Precautions

The data migration does not affect the data of the source RDS instance. During the data migration, DTS reads the data of the source RDS instance and replicates the data to the destination RDS instance. DTS does not delete the data of the source RDS instance. For more information, see Design concept of data migration.
DTS uses read and write resources of the source and destination databases during full data migration. This may increase the loads of the database servers. If the database performance is unfavorable, the specification is low, or the data volume is large, database services may become unavailable. For example, DTS occupies a large amount of read and write resources in the following cases: a large number of slow SQL queries are performed on the source database, the tables have no primary keys, or a deadlock occurs in the destination database. 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. For example, you can migrate data when the CPU utilization of the source and destination databases is less than 30%.
The tables to be migrated in the source database must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records.
For data consistency purposes, we recommend that you do not write data to the source RDS instance during the data migration. This applies if you select the full data migration type.
If the data migration task fails, DTS can automatically resume the task. Before you switch your workloads over to the destination RDS instance, you must stop or release the data migration task. Otherwise, the data on the source RDS instance overwrites the data on the destination RDS instance after the data migration task is resumed.
DTS automatically creates databases on the destination RDS instance. If the name of a source database is invalid, you must log on to the destination RDS instance and create a destination database for that source database. This is required before you create the data migration task. In addition, the name of the created destination database must comply with the database naming conventions of Alibaba Cloud.

Note For more information about how to create a database and the database naming conventions, see Create accounts and databases for an ApsaraDB RDS instance that runs SQL Server 2017 EE.
After the switchover of your workloads is complete, new log sequence numbers (LSNs) on the destination RDS instance do not increment from the largest LSN that is generated on the source RDS instance. Therefore, before you start the switchover, you must obtain the largest LSN that is generated on the source RDS instance. Then, you must specify the obtained LSN as the start LSN on the destination RDS instance. You can run the following commands to obtain the largest LSN that is generated on the source RDS instance:
```
do language plpgsql $$
declare
  nsp name;
  rel name;
  val int8;
begin
  for nsp,rel in select nspname,relname from pg_class t2 , pg_namespace t3 where t2.relnamespace=t3.oid and t2.relkind='S'
  loop
    execute format($_$select last_value from %I.%I$_$, nsp, rel) into val;
    raise notice '%',
    format($_$select setval('%I.%I'::regclass, %s);$_$, nsp, rel, val+1);
  end loop;
end;
$$;
```

Billing


Migration type	Task configuration fee	Internet traffic fee
Schema migration and full data migration	Free of charge.	Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Pricing.
Incremental data migration	Charged. For more information, see Pricing.

Migration types

Schema migration
DTS migrates the schemas of the required objects to the destination instance.
Full data migration
DTS migrates historical data of the required objects from the source RDS instance to the destination RDS instance.
Incremental data migration
After full data migration is complete, DTS synchronizes incremental data from the source RDS instance to the destination RDS instance. Incremental data migration allows you to ensure service continuity when you migrate data between RDS instances.

SQL operations that can be synchronized during incremental data migration


Migration scenario	Operation type	SQL statements
Migrate data between ApsaraDB RDS for MySQL instances Migrate data between ApsaraDB RDS for MariaDB TX instances Migrate data from an ApsaraDB RDS for MariaDB TX instance to an ApsaraDB RDS for MySQL instance	DML	INSERT, UPDATE, DELETE, and REPLACE
	DDL	ALTER TABLE and ALTER VIEW CREATE FUNCTION, CREATE INDEX, CREATE PROCEDURE, CREATE TABLE, and CREATE VIEW DROP INDEX and DROP TABLE RENAME TABLE TRUNCATE TABLE
Migrate data between ApsaraDB RDS for SQL Server instances	DML	INSERT, UPDATE, and DELETE Note DTS does not synchronize the UPDATE operations that update only the large fields.
Migrate data between ApsaraDB RDS for SQL Server instances	DDL	ALTER TABLE, including only ADD COLUMN, DROP COLUMN, and RENAME COLUMN CREATE TABLE and CREATE INDEX Note If a CREATE TABLE operation creates a partition table or a table that contains functions, DTS does not synchronize the operation. DROP TABLE RENAME TABLE TRUNCATE TABLE
Migrate data between ApsaraDB RDS for PostgreSQL instances Migrate data between ApsaraDB RDS for PPAS instances	DML	INSERT, UPDATE, and DELETE
	DDL	ALTER TABLE and ADD INDEX CREATE TABLE and CREATE INDEX Note If a CREATE TABLE operation creates a partition table or a table that contains functions, DTS does not synchronize the operation. DROP TABLE RENAME TABLE

Permissions required for database accounts


Migration scenario	Database	Schema migration	Full data migration	Incremental data migration
Migrate data between ApsaraDB RDS for MySQL instances Migrate data between ApsaraDB RDS for MariaDB TX instances Migrate data from an ApsaraDB RDS for MariaDB TX instance to an ApsaraDB RDS for MySQL instance	Source instance	The SELECT permission	The SELECT permission	The REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions
	Destination instance	The read and write permissions	The read and write permissions	The read and write permissions
Migrate data between ApsaraDB RDS for SQL Server instances	Source instance	The SELECT permission	The SELECT permission	The sysadmin permission
Migrate data between ApsaraDB RDS for SQL Server instances	Destination instance	The read and write permissions	The read and write permissions	The read and write permissions
Migrate data between ApsaraDB RDS for PostgreSQL instances	Source instance	The usage permission on pg_catalog	The SELECT permission on the objects to be migrated	superuser
Migrate data between ApsaraDB RDS for PostgreSQL instances	Destination instance	The create and usage permissions on the objects to be migrated	The permissions of the database owner, including the permissions to perform the INSERT, UPDATE, and DELETE operations Note A standard account of an ApsaraDB RDS for PostgreSQL instance has the required permissions.	The permissions of the database owner, including the permissions to perform the INSERT, UPDATE, and DELETE operations Note A standard account of an ApsaraDB RDS for PostgreSQL instance has the required permissions.
Migrate data between ApsaraDB RDS for PPAS instances	Source instance	The usage permission on pg_catalog	The SELECT permission on the objects to be migrated	superuser
Migrate data between ApsaraDB RDS for PPAS instances	Destination instance	The create and usage permissions on the objects to be migrated	The owner permission on schemas	The owner permission on schemas

Procedure

Log on to the DTS console.
In the left-side navigation pane, click Data Migration.
At the top of the Migration Tasks page, select the region where the destination RDS instance resides.
In the upper-right corner of the page, click Create Migration Task.

Configure the source and destination RDS instances. Migrate data between RDS instances


Section	Parameter	Description
None	Task Name	Enter the name that DTS generates for the data migration task. We recommend that you specify an informative name for easy identification. You do not need to specify a unique name.
Source Database	Instance Type	Select RDS Instance.
	Instance Region	Select the region where the source RDS instance resides.
	RDS Instance ID	Select the ID of the source RDS instance. Note The source and destination RDS instances can be the same or different. In theory, you can use DTS to migrate data within the same RDS instance or between two different RDS instances.
	Database Name	Enter the name of the source database on the source RDS instance. Note This parameter appears and needs to be set only when the source RDS instance runs PostgreSQL.
	Database Account	Enter the username of the account that you want to use to log on to the source RDS instance. For more information about the permissions required for the account, see Permissions required for database accounts.
	Database Password	Enter the password of the account that you want to use to log on to the source RDS instance. Note After you specify the source database parameters, click Test Connectivity next to Database Password to verify whether the specified parameters are valid. If the specified parameters are valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Modify the source database parameters based on the check results.
	Encryption	The type of connection that you want to establish. Select Non-encrypted or SSL-encrypted. If you select SSL-encrypted, you must enable SSL encryption for the source RDS instance before you create the data migration task. For more information, see Configure SSL encryption on an ApsaraDB RDS for SQL Server instance. Note This parameter appears and needs to be set only when the source RDS instance runs MySQL. The Encryption parameter is supported only in the Alibaba Cloud regions in mainland China and in the China (Hong Kong) region.
Destination Database	Instance Type	Select RDS Instance.
	Instance Region	Select the region where the destination RDS instance resides.
	RDS Instance ID	Select the ID of the destination RDS instance. Note The source and destination RDS instances can be the same or different. In theory, you can use DTS to migrate data within the same RDS instance or between two different RDS instances.
	Database Name	Enter the name of the destination database on the destination RDS instance. The name of the destination database can be different from the name of the source database. Note This parameter appears and needs to be set only when the destination RDS instance runs PostgreSQL.
	Database Account	Enter the username of the account that you want to use to log on to the destination RDS instance. For more information about the permissions required for the account, see Permissions required for database accounts.
	Database Password	Enter the password of the account that you want to use to log on to the destination RDS instance. Note After you specify the destination database parameters, click Test Connectivity next to Database Password to verify whether the parameters are valid. If the specified parameters are valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Modify the destination database parameters based on the check results.
	Encryption	The type of connection that you want to establish. Select Non-encrypted or SSL-encrypted. If you select SSL-encrypted, you must enable SSL encryption for the destination RDS instance before you create the data migration task. For more information, see Configure SSL encryption on an ApsaraDB RDS for SQL Server instance. Note This parameter appears and needs to be set only when the destination RDS instance runs MySQL. The Encryption parameter is supported only in the Alibaba Cloud regions in mainland China and in the China (Hong Kong) region.

In the lower-right corner of the page, click Set Whitelist and Next.

Note In this step, DTS adds the IP address of the DTS server to the IP address whitelists of the source and destination RDS instances. This way, the DTS server can connect to the source and destination RDS instances.

Select the migration types and the objects that you want to migrate.

Select the migration types and the migration objects


Parameter	Description
Migration Types	Select the migration types based on your business requirements. The migration types must be supported by the database engine that is used. If you want to migrate only the existing full data, select Schema Migration and Full Data Migration. If you want to migrate data without downtime, select Schema Migration, Full Data Migration, and Incremental Data Migration. Note If the Incremental Data Migration type is not selected, do not write data to the source RDS instance during the data migration. This ensures data consistency between the source and destination RDS instances.
Available	Select one or more objects from the Available section and click the icon to move the selected objects to the Selected section. Note You can select columns, tables, or databases 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, and stored procedures to the destination database. By default, after an object is migrated to the destination database, the name of the object remains unchanged. You can use the object name mapping feature to change the names of the objects that are migrated to the destination database. For more information, see Object name mapping. If you use the object name mapping feature on an object, other objects that are dependent on the object may fail to be migrated.

Click Precheck.
Note
- A precheck is performed before the migration task starts. The migration task only starts after the precheck succeeds.
- If the precheck fails, click the icon next to each failed check item to view the related details. Fix the issues as instructed and run the precheck again.
After the task passes the precheck, click Next.
In the Confirm Settings dialog box, specify the Channel Specification and select Data Transmission Service (Pay-As-You-Go) Service Terms.
Click Buy and Start to start the data migration task.
- Full data migration
  We recommend that you do not manually stop the task during full data migration. Otherwise, the data migrated to the destination instance will be incomplete. You can wait until the data migration task automatically stops.
- Incremental data migration
  The task does not automatically stop during incremental data migration. You must manually stop the task.
  
  Note We recommend that you select an appropriate time to manually stop the data migration task. For example, you can stop the task during off-peak hours or before you switch your workloads to the destination instance.
  1. Wait until Incremental Data Migration and The migration task is not delayed appear in the progress bar of the migration task. Then, stop writing data to the source database for a few minutes. The delay time of incremental data migration may be displayed in the progress bar.
  2. After the status of incremental data migration changes to The migration task is not delayed again, manually stop the migration task.