|Limits on the source database
- The server to which the source database belongs must have sufficient outbound bandwidth.
Otherwise, the data migration speed decreases.
- If the source database is connected over Express Connect, you must specify a VIP for
the database when you configure the source database information.
- If the source database is an Oracle RAC database hosted on Elastic Compute Service
(ECS) or connected over Express Connect, VPN Gateway, Smart Access Gateway, Database
Gateway, or Cloud Enterprise Network (CEN), you can use a single VIP rather than a
Single Client Access Name (SCAN) IP address when you configure the source database
information. After you specify the VIP, node failover is not supported for the Oracle
- Requirements for the objects to migrate:
- The tables to migrate must have PRIMARY KEY or UNIQUE constraints and all fields must
be unique. Otherwise, the destination database may contain duplicate data records.
- If the version number of your Oracle database is 12c or later, the names of the tables
to migrate cannot exceed 30 bytes in length.
- If you select tables as the objects to migrate and you want to edit the 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 split the
tables and configure multiple tasks to migrate the tables, or configure a task to
migrate the entire database.
- If you want to migrate incremental data, you must make sure that the following requirements
- The redo logging and archive logging must be enabled.
For an incremental data migration task, redo logs and archive logs of the source database
must be stored for more than 24 hours. For a full data and incremental data migration
task, redo logs and archive logs of the source database must be stored for at least
seven days. After the full data migration is completed, you can set the retention
period to more than 24 hours. Otherwise, Data Transmission Service (DTS) may fail
to obtain the redo logs and archive logs, and the task may fail. In exceptional circumstances,
data inconsistency or loss may occur. Make sure that you set the retention period
of redo logs and archive logs in accordance with the preceding requirements. Otherwise,
the Service Level Agreement (SLA) of DTS does not ensure service reliability and performance.
- Limits on operations:
- 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 you perform only full data migration, do not write data to the source database
during data migration. Otherwise, data inconsistency between the source and destination
databases occurs. To ensure data consistency, we recommend that you select schema
migration, full data migration, and incremental data migration as the migration types.
- During data migration, do not update LONGTEXT fields. Otherwise, the data migration
- 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 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 completed, the tablespace
of the destination database is larger than that of the source database.
- DTS attempts to resume data migration tasks that failed within the last seven days.
Before you switch workloads over to the destination instance, stop or release the
data migration task. You can also execute the
REVOKE statement to revoke write permissions from the accounts used by DTS to access the
destination instance. Otherwise, the data in the source database overwrites the data
in the destination instance after the task is resumed.
||If the destination database runs on a PolarDB for MySQL cluster, take note of the
- Table names in the PolarDB for MySQL cluster are case-insensitive. If a table name
in the source Oracle database contains uppercase letters, PolarDB for MySQL converts
all uppercase letters to lowercase letters before a table is created.
If the source Oracle database contains identical table names that differ only in capitalization,
these table names are identified as duplicate. During schema migration, the following
message is returned: "The object already exists". To prevent name conflicts in the
destination database, you can use the object name mapping feature to capitalize the
table names. For more information, see Object name mapping.
- DTS automatically creates a destination database in the PolarDB for MySQL cluster.
However, if the name of the source database is invalid, you must create a database
in the PolarDB for MySQL cluster before you configure the data migration task. For
more information, see Database Management.