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 |
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 How DTS works in data migration mode.
- 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 from the source RDS instance to the destination RDS 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 |
---|---|---|
|
DML | INSERT, UPDATE, DELETE, and REPLACE |
DDL |
|
|
Migrate data between ApsaraDB RDS for SQL Server instances | DML | INSERT, UPDATE, and DELETE
Note If an UPDATE operation updates only the large fields, DTS does not synchronize the
operation.
|
DDL |
|
|
Migrate data between ApsaraDB RDS for PostgreSQL instances |
DML | INSERT, UPDATE, and DELETE |
DDL |
|
Permissions required for database accounts
Migration scenario | Database | Schema migration | Full data migration | Incremental data migration |
---|---|---|---|---|
|
Source instance | The SELECT permission | The SELECT permission | The REPLICATION SLAVE, REPLICATION CLIENT, 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 owner permission on the objects to be migrated
Note A privileged account has the required permissions.
|
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 | rds_superuser
Note
|
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.
|
Procedure
- Log on to the DTS console.
- In the left-side navigation pane, click Data Migration.
- In the upper part of the Migration Tasks page, select the region where the RDS instance resides.
- In the upper-right corner of the page, click Create Migration Task.
- Configure the source and destination 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 information about the self-managed Oracle database, you can click Test Connectivity next to Database Password to check whether the information is valid. If the information is valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Then, modify the information 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. NoteThis 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 information about the RDS instance, you can click Test Connectivity next to Database Password to check whether the information is valid. If the information is valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Then, modify the information 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.
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 data migration task passes the precheck, click Next.
- In the Confirm Settings dialog box, configure the Channel Specification parameter. Then, read and select Data Transmission Service (Pay-as-you-go) Service Terms.
- Click Buy and Start to start the data migration task.
- Full data migration
Do not manually stop a full data migration task. If you manually stop a full data migration task, the data that is migrated to the RDS instance may be incomplete. You can wait until the full data migration task automatically stops.
- Incremental data migration
An incremental data migration task does not automatically stop. You must manually stop the task.
Note We recommend that you manually stop an incremental data migration task at an appropriate point in time. For example, you can stop the task during off-peak hours or before you switch your workloads over to the RDS instance.- Wait until Incremental Data Migration and The data migration task is not delayed appear in the progress bar of the data migration task. Then, stop writing data to the self-managed Oracle database for a few minutes. The delay time of incremental data migration may be displayed in the progress bar.
- Wait until the status of incremental data migration changes to The data migration task is not delayed again. Then, manually stop the migration task.
- Full data migration