This topic describes how to migrate data from an ApsaraDB RDS for PPAS instance to a PolarDB for Oracle 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 for Oracle cluster is created. For more information, see Create a PolarDB for Oracle cluster.
- The available storage space of the PolarDB for Oracle cluster is larger than the total size of the data in the ApsaraDB RDS for PPAS instance.
- If one or more uppercase letters exist in the names of the source database, tables, and fields in the ApsaraDB RDS for PPAS instance, you must enclose the names of the source database, tables, and fields in the PolarDB for Oracle cluster with double quotation marks (") when you create the objects in the cluster.
- To migrate incremental data from an ApsaraDB RDS for PPAS instance, you must grant the permissions of the superuser role to the database account.
Limits
- 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.
- 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 cluster, stop or release the data migration task. Otherwise, the data in the source database overwrites the data in the destination cluster 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 execute the following statements to query the maximum value of the sequences
in the source database:
do language plpgsql $$ declare nsp name; rel name; val int8; begin for nsp,rel in select nspname,relname from pg_class t2 , pg_namespace t3 where t2.relnamespace=t3.oid and t2.relkind='S' loop execute format($_$select last_value from %I.%I$_$, nsp, rel) into val; raise notice '%', format($_$select setval('%I.%I'::regclass, %s);$_$, nsp, rel, val+1); end loop; end; $$;
- When you migrate data from your ApsaraDB RDS for PPAS instance to a PolarDB for Oracle
cluster, take note of the following items:
- Make sure that the specifications of the PolarDB for Oracle cluster are higher than or equal to those of the ApsaraDB RDS for PPAS instance. Otherwise, slow SQL queries or out of memory (OOM) errors may occur because of insufficient CPU or memory resources after you migrate the data to the PolarDB for Oracle cluster. For more information about the recommended specifications of PolarDB for Oracle clusters, see Mapping between specifications of ApsaraDB RDS for PPAS instances and recommended specifications of PolarDB for Oracle clusters.
- If you have business requirements for the number of connections and IOPS after migration, select appropriate specifications based on your business requirements. For more information, see Specifications of compute nodes.
- If you use a cluster endpoint to connect your application to a PolarDB for Oracle cluster, read/write splitting is enabled. Then, the system forwards read requests to read-only PolarDB for Oracle nodes. This reduces the load on the PolarDB for Oracle cluster. For more information about how to obtain a cluster endpoint, see View or apply for an endpoint.
Mapping between specifications of ApsaraDB RDS for PPAS instances and recommended specifications of PolarDB for Oracle clusters
Make sure that the specifications of the PolarDB for Oracle cluster are higher than or equal to the specifications of your ApsaraDB RDS for PPAS instance. Otherwise, slow SQL queries or OOM errors may occur because of insufficient CPU or memory resources after you migrate the data to the PolarDB for Oracle cluster. The following table lists the recommended specifications of PolarDB for Oracle clusters.
Specifications of ApsaraDB RDS for PPAS instances | Recommended specifications of PolarDB for Oracle clusters | ||
---|---|---|---|
Instance type | CPU and memory | Instance type | CPU and memory |
rds.ppas.t1.small | 1 core, 1 GB | polar.o.x4.medium | 2 cores, 8 GB |
ppas.x4.small.2 | 1 core, 4 GB | polar.o.x4.medium | 2 cores, 8 GB |
ppas.x4.medium.2 | 2 cores, 8 GB | polar.o.x4.medium | 2 cores, 8 GB |
ppas.x8.medium.2 | 2 cores, 16 GB | polar.o.x4.large | 4 cores, 16 GB |
ppas.x4.large.2 | 4 cores, 16 GB | polar.o.x4.large | 4 cores, 16 GB |
ppas.x8.large.2 | 4 cores, 32 GB | polar.o.x4.xlarge | 8 cores, 32 GB |
ppas.x4.xlarge.2 | 8 cores, 32 GB | polar.o.x4.xlarge | 8 cores, 32 GB |
ppas.x8.xlarge.2 | 8 cores, 64 GB | polar.o.x8.xlarge | 8 cores, 64 GB |
ppas.x4.2xlarge.2 | 16 cores, 64 GB | polar.o.x8.2xlarge | 16 cores, 128 GB |
ppas.x8.2xlarge.2 | 16 cores, 128 GB | polar.o.x8.2xlarge | 16 cores, 128 GB |
ppas.x4.4xlarge.2 | 32 cores, 128 GB | polar.o.x8.4xlarge | 32 cores, 256 GB |
ppas.x8.4xlarge.2 | 32 cores, 256 GB | polar.o.x8.4xlarge | 32 cores, 256 GB |
rds.ppas.st.h43 | 60 cores, 470 GB | polar.o.x8.8xlarge | 64 cores, 512 GB memory |
Migration types
Migration type | Description |
---|---|
Schema migration | DTS migrates the schemas of the required objects from the source database to the destination
PolarDB cluster. DTS supports schema migration for the following types of objects:
table, view, synonym, trigger, stored procedure, stored function, package, and user-defined
type.
Important DTS does not support triggers for this migration type. If an object contains triggers,
data inconsistency between the source and destination databases may occur.
|
Full data migration | DTS migrates the historical data of the required objects from the source database
to the destination PolarDB cluster.
Important During schema migration and full data migration, do not perform DDL operations on
the objects to be migrated. Otherwise, the objects may fail to be migrated.
|
Incremental data migration | DTS retrieves redo log files from the source database. Then, DTS migrates incremental
data from the source database to the destination PolarDB cluster. DTS can synchronize
DML operations, such as INSERT, UPDATE, and DELETE. DTS cannot synchronize DDL operations.
Incremental data migration allows you to ensure service continuity when you perform data migration. |
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 Billing overview. |
Incremental data migration | Charged. For more information, see Billing overview. |
Permissions required for database accounts
Log on to the source Oracle database, create an account for data collection, and grant permissions to the account.
Database | Schema migration | Full data migration | Incremental data migration |
---|---|---|---|
ApsaraDB RDS for PPAS instance | Read permissions | Read permissions | Permissions of the superuser role |
PolarDB for Oracle cluster | Permissions of the schema owner | Permissions of the schema owner | Permissions of the schema owner |
To create a database account and grant permissions to the database account, perform the following operations:
To create a database account in a PolarDB for Oracle cluster, follow the instructions in Create database accounts