|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 collections as the objects to be migrated and you need to edit collections
(such as renaming collections), up to 1,000 collections can be migrated in a single
data migration task. If you run a task to migrate more than 1,000 collections, a request
error occurs. In this case, we recommend that you split the collections to be migrated,
configure multiple tasks to migrate the collections, or configure a task to migrate
the entire database.
- If you need to migrate incremental data, you must make sure that the following requirements
- The oplog is enabled. Otherwise, error messages are returned during precheck and the
data migration task cannot be started.
If you perform only incremental data migration, the oplogs of the source database
must be stored for more than 24 hours. If you perform both full data migration and
incremental data migration, the oplogs of the source database must be stored for at
least seven days. After full data migration is completed, you can set the retention
period to more than 24 hours. Otherwise, DTS may fail to obtain the oplogs and the
task may fail. In extreme cases, data may be inconsistent or lost. Make sure that
you set the retention period of oplogs based on the preceding requirements. Otherwise,
the Service Level Agreement (SLA) of DTS does not guarantee service reliability and
- Limits on operations:
- During schema migration and full data migration, do not change the schemas of databases
or collections. 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.
- To ensure compatibility, the version of the destination MongoDB database must be the
same as or later than the version of the source MongoDB database. If the version of
the destination database is earlier than the version of the source database, database
compatibility issues may occur.
- DTS cannot migrate data from the admin or local database.
- Transaction information is not retained. When transactions are migrated to the destination
database, they are converted into a single record.
- 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
collections of the destination database. After full data migration is completed, the
storage space for collections of the destination database is larger than that of the
- 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 MongoDB 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
update 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 an update operation on the source database to update the latency.
Note If you select an entire database as the object to be migrated, you can create a heartbeat.
The heartbeat is updated or receives data every second.