|Limits on the source database
- The server to which the source database belongs must have sufficient outbound 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 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 migrate the tables in batches, or configure a task to migrate the entire
- You can run a single data migration task to migrate up to 10 databases. If you need
to migrate more than 10 databases, we recommend that you configure multiple tasks
to migrate the databases in batches. Otherwise, the performance and stability of your
data migration task may be compromised.
- If you need to migrate incremental data, make sure that the following requirements
- The data logging feature must be enabled. The backup mode must be set to Full, and
full logical backup must be performed.
If you perform only incremental data migration, the data logs of the source database
must be stored for more than 24 hours. If you perform both full data migration and
incremental data migration, the data logs of the source database must be stored for
at least seven days. Otherwise, DTS may fail to obtain the data 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 data logs based on the preceding
requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not guarantee
service reliability or performance.
- If the change data capture (CDC) feature needs to be enabled for the tables to be
migrated in the source database, the following conditions must be met. Otherwise,
the precheck fails.
- The value of the srvname field in the sys.sysservers view is the same as the return
value of the SERVERPROPERTY function.
- If the source database is a self-managed SQL Server database, the database owner must
be the sa user. If the source database is an ApsaraDB RDS for SQL Server database,
the database owner must be the sqlsa user.
- If the source database is of Enterprise Edition, you must use SQL Server 2008 or later.
- If the source database is of Standard Edition, you must use SQL Server 2016 SP1 or
- If the source database is of Standard Edition or Enterprise Edition and its version
is SQL Server 2017, we recommend that you update the version.
- Limits on operations to be 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.
- DTS does not migrate data of the following types: CURSOR, ROWVERSION, SQL_VARIANT,
HIERACHYID, and GEOMETRY.
- If you select Incremental Synchronization Based on Logs of Source Database as SQL Server Incremental Synchronization Mode in the Configure Objects and Advanced Settings step, the tables to be migrated must have clustered indexes that contain primary
key columns. In addition, the table to be migrated cannot be compressed tables or
contain computed columns. Ignore the preceding limits if the hybrid log parsing mode
- If you migrate data between different versions of databases, make sure that the database
versions are compatible.
- In the Incremental Synchronization Based on Logs of Source Database mode, DTS adds
a heartbeat table named dts_log_heart_beat to the source database to ensure that the
latency of data migration is accurate. In the hybrid log-based parsing incremental
synchronization mode, DTS creates a trigger named dts_cdc_sync_ddl, a heartbeat table
named dts_sync_progress, and a DDL history table named dts_cdc_ddl_history and enables
CDC for the source database and some tables.
- 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 on 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 database, 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 database. Otherwise, the data in the source database overwrites the
data in the destination database after the task is resumed.
- If the data migration task involves incremental data migration, DTS does not allow
you to perform the reindexing operation. If you perform the reindexing operation,
the data migration task may fail, or even data loss may occur.
- If the number of CDC-enabled tables to be migrated in a single migration task exceeds
1,000, the precheck fails.
- To perform incremental data migration, you must disable the trigger and foreign keys
in the destination database. Otherwise, the data migration task fails.
||If the destination instance is an ApsaraDB RDS for SQL Server instance, take note
of the following limits:
DTS automatically creates a destination database in the ApsaraDB RDS for SQL Server
instance. However, if the name of the database to be migrated does not conform to
the naming conventions of ApsaraDB RDS, you must manually create a database in the
destination ApsaraDB RDS for SQL Server instance before you configure the data migration
task. For more information, see Create a database on an ApsaraDB RDS for SQL Server instance.