This topic describes how to migrate data from an ApsaraDB RDS for PPAS database to a PolarDB-O cluster by using Data Transmission Service (DTS). 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
- A PolarDB-O cluster is created. For more information, see Create a PolarDB-O cluster.
- The available storage space of the PolarDB-O cluster is larger than the total size of the data in the ApsaraDB RDS for PPAS database.
- To migrate incremental data from an ApsaraDB RDS for PPAS database, you must submit a ticket to grant the superuser permission to the database account.
Precautions
- DTS uses read and write resources of the source and destination databases during full data migration. This may increase the load of the database server. 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.
- 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 a data migration task fails, DTS automatically resumes the task. Before you switch your workloads to the destination database, stop or release the data migration task. Otherwise, the data in the source database will overwrite the data in the destination database after the task is resumed.
- 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 starting value of the sequences in the destination database.
You can run the following statements to query the maximum value of the sequences in
the source database:
do language plpgsql $$ declare nsp name; rel name; val int8; begin for nsp,rel in select nspname,relname from pg_class t2 , pg_namespace t3 where t2.relnamespace=t3.oid and t2.relkind='S' loop execute format($_$select last_value from %I.%I$_$, nsp, rel) into val; raise notice '%', format($_$select setval('%I.%I'::regclass, %s);$_$, nsp, rel, val+1); end loop; end; $$;
Migration types
Migration type | Description |
---|---|
Schema migration | DTS migrates the schemas of the required objects from the source database to the destination
PolarDB-O cluster. DTS supports schema migration for the following types of objects:
table, view, synonym, trigger, stored procedure, function, package, and user-defined
type.
Notice However, if an object contains triggers, data will become inconsistent between the
source and destination databases.
|
Full data migration | DTS migrates historical data of the required objects from the source database to the
destination PolarDB-O cluster.
Notice During schema migration and full data migration, do not perform data definition language
(DDL) operations on the required objects. Otherwise, the objects may fail to be migrated.
|
Incremental data migration | DTS retrieves redo log files from the source database. Then, DTS synchronizes incremental
data from the source database to the destination PolarDB-O cluster. DTS can synchronize
data manipulation language (DML) operations, including INSERT, UPDATE, and DELETE
operations. DTS cannot synchronize DDL operations.
Incremental data migration allows you to ensure service continuity when you migrate data from an ApsaraDB RDS for PPAS database to a PolarDB-O cluster. |
Billing
Migration type | Instance configurations | Internet traffic |
---|---|---|
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. |
Permissions required for database accounts
Database | Schema migration | Full data migration | Incremental data migration |
---|---|---|---|
ApsaraDB RDS for PPAS | The read permission | The read permission | The superuser permission |
PolarDB-O | The owner permission on schemas | The owner permission on schemas | The owner permission on schemas |
For more information about how to create and authorize a database account, see the following topics:
- ApsaraDB RDS for PPAS: Create an account on an ApsaraDB RDS for PPAS instanceNotice To migrate incremental data from an ApsaraDB RDS for PPAS database, you must submit a ticket to grant the superuser permission to the database account.
- PolarDB-O: Create database accounts