|Limits on the source database
- The server to which the source database belongs must have sufficient outbound bandwidth.
Otherwise, the data migration speed decreases.
- 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 the tables,
such as renaming tables or columns, in the destination database, you can migrate up
to 1,000 tables 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 configure
multiple tasks to synchronize the tables in batches or configure a task to synchronize
the entire database.
- If you want to migrate incremental data, make sure that the following requirements
- The binary logging feature must be enabled. The value of the loose_polar_log_bin parameter
must be set to on. Otherwise, error messages are returned during precheck and the
data migration task cannot be started.
For an incremental data migration task, the binary logs of the source database are
retained for at least 24 hours. For a full data and incremental data migration task,
the binary logs of the source database are retained for at least seven days. Otherwise,
Data Transmission Service (DTS) may fail to obtain the binary logs and the task may
fail. In exceptional circumstances, data inconsistency or loss may occur. After full
data migration is complete, you can set the retention period to more than 24 hours.
Make sure that you set the retention period of binary logs based on the preceding
requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not ensure
service reliability and performance.
- Limits on operations that are performed on the source database:
- 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 may occur. To ensure data consistency, we recommend that you select schema
migration, full data migration, and incremental data migration as the migration types.
- Read-only nodes of the source PolarDB for MySQL cluster cannot be migrated.
- 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 the read and write resources
of the source and destination databases. This may increase the loads of the database
- During full data migration, concurrent INSERT operations cause fragmentation in the
tables of the destination database. After full data migration is complete, the size
of used tablespace of the destination database is larger than that of the source database.
- Make sure that the precision settings for columns of the FLOAT or DOUBLE data type
meet 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 execute the
REVOKE statement to revoke the write permissions from the accounts used by DTS to access
the destination instance. Otherwise, the data in the source database will overwrite
the data in the destination database after the task is resumed.
- DTS executes the CREATE DATABASE IF NOT EXISTS `test` statement in the source database as scheduled to move forward the binary log file
||If you migrate data to an ApsaraDB RDS for MySQL instance, DTS automatically creates
a destination database in the ApsaraDB RDS for MySQL instance. However, if the name
of the source database is invalid, you must manually create a database in the ApsaraDB
RDS for MySQL instance before you configure the data migration task. For more information,
see Create a database on an ApsaraDB RDS for MySQL instance.