|Limits on the source database
- Bandwidth requirements: The server to which the source database belongs must have
sufficient egress bandwidth. Otherwise, the data migration speed is affected.
- Requirements for the objects to be migrated:
- 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.
- If the version of your Oracle database is 12c or later, the names of the tables to
be migrated cannot exceed 30 bytes in length.
- If you want to migrate incremental data, you must make sure that the following requirements
- The data logging feature must be enabled.
Data logs are retained for at least 7 days during full data migration. You can wait
until full data migration is complete, and then clear the data logs generated in the
source database after the DTS task is run.
Note To ensure data security, DTS stores only 50 GB of data logs or the data logs for the
last 24 hours. If the limit is exceeded, DTS automatically clears the cached logs.
Warning If you clear the data logs of the source database during full data migration, the
task may fail to migrate incremental data. For example, full data migration takes
more than 24 hours due to the large data volume in the source database and abnormal
writing in the destination database. In this case, if the data logs of the source
database are cleared during full data migration, DTS cannot obtain the data logs generated
24 hours ago. Therefore, the data migration task may fail.
- Limits on operations:
- During schema migration and full data migration, do not perform data definition language
(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 will be inconsistent between the source and
destination databases. To ensure data consistency, we recommend that you select Schema
Migration, Full Data Migration, and Incremental Data Migration as the migration types.
- 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 complete, 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 to the destination instance, stop or release the data
migration task. You can also run the
revoke command to revoke the write permissions from the accounts that are used by DTS to
access the destination instance. Otherwise, the data in the source database will overwrite
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 creating the table.
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 avoid 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 manually create a
database in the PolarDB for MySQL cluster before you configure the data migration
task. For more information, see Databases.