|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 migrate 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 migrate and you need to edit 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 binary logging feature is enabled. The value of the binlog_format parameter is
set to row. The value of the binlog_row_image parameter is set to full. Otherwise,
error messages are returned during precheck and the data migration task cannot be
Notice If the self-managed MySQL database is deployed in a dual-primary cluster, you must
set log_slave_updates to ON. This ensures that Data Transmission Service (DTS) can
obtain all binary logs.
For an incremental data migration task, binary logs of the source database must be
stored for more than 24 hours. For a full data and incremental data migration task,
binary logs of the source database must be stored for at least seven days. After full
data migration is complete, you can set the retention period to more than 24 hours.
Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional
circumstances, data inconsistency or loss may occur. 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:
- 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.
- During data migration, do not perform DDL operations to add comments. 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 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.
- 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 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 size
of used 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 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 overwrites 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
DML operation is performed on the source database for a long time, the migration latency
may be inaccurate. If the latency of the synchronization task is too high, you can
perform a DML operation on the source database to update the latency.
Note If you select an entire database as the object to migrate, you can create a heartbeat
table. The heartbeat table is updated or receives data every second.