|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.
- The tables to be migrated must have PRIMARY KEY or UNIQUE constraints and all fields
must be unique. Otherwise, the destination database may contain duplicate data records.
- If you select tables as the objects to be migrated and you need to edit tables (such
as rename tables or columns), 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 to be migrated, configure
multiple tasks to migrate the tables, or call DTS API operations to configure tasks.
- If you want to migrate incremental data, you must make sure that the following requirements
- The binary logging feature must be enabled. The value of the binlog_format parameter
must be set to row. The value of the binlog_row_image parameter must be set to full.
Otherwise, error messages are returned during precheck and the data migration task
cannot be started.
- Binary 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 binary logs generated in
the source database after the DTS task is run.
Note DTS stores only 50 GB of binary logs or the binary logs for the last 24 hours. If
the limit is exceeded, DTS automatically clears the cached logs.
Warning If you clear the binary logs of the source database during full data migration, the
data migration task may fail. 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 binary logs of the source database
are cleared during full data migration, DTS cannot obtain the binary 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.
- During data migration, do not perform DDL operations to add comments, for example,
ALTER TABLE table_name COMMENT='Table comment';. 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.
- Prefix indexes cannot be migrated. If the source database contains prefix indexes,
data may fail to be migrated.
- Due to the limits of AnalyticDB for MySQL, if the disk space usage of the nodes in an AnalyticDB for MySQL cluster reaches 80%, the task is delayed and error messages are returned. We recommend
that you estimate the required disk space based on the objects that you want to migrate.
You must make sure that the destination cluster has sufficient storage space.
- 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.
- You must make sure that the precision settings for columns of the FLOAT or DOUBLE
data type meets your business requirements. DTS uses the
ROUND(COLUMN,PRECISION) function to retrieve values from columns of the FLOAT or DOUBLE data type. If you
do not specify a precision, DTS sets the precision for the FLOAT data type to 38 digits
and the precision for the DOUBLE data type to 308 digits.
- 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 source database is a self-managed MySQL database, take note of the following
- If you perform a primary/secondary switchover on the source database when the data
migration task is running, the task fails.
- DTS calculates migration latency based on the timestamp of the latest migrated data
in the destination database and the current timestamp in the source database. If no
data manipulation language (DML) operation is performed on the source database for
a long time, the migration latency may be inaccurate. If the latency of the migration
task is too high, you can perform a DML operation on the source database to update
Note If you select an entire database as the object to be migrated, you can create a heartbeat
table. The heartbeat table is updated or receives data every second.