Category | Description |
Limits on the source database | The server on which the source database is deployed 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 in the destination database, such as renaming tables or columns, 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 or configure a task to migrate the entire database. You can run a single data migration task to migrate up to 10 databases. If you want to migrate more than 10 databases, we recommend that you configure multiple tasks to migrate the databases. Otherwise, the performance and stability of your data migration task may be compromised. If you want to migrate incremental data, make sure that the following requirements are met: The data logging feature must be enabled. The backup mode must be set to Full and full physical backup must be performed. If you perform only incremental data migration, the data logs of the source database must be retained 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 retained for at least seven days. Otherwise, Data Transmission Service (DTS) may fail to obtain the data logs and the task may fail. In some cases, data inconsistency or loss may even 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 that you want to migrate from 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 the Enterprise edition, you must use SQL Server 2008 or later. If the source database is of the Standard edition, you must use SQL Server 2016 SP1 or later. If the source database is of the Standard or Enterprise edition and its version is SQL Server 2017, we recommend that you update the version.
DTS uses the fn_log function to obtain the logs of the source database. However, this function has performance bottlenecks. We recommend that you do not clear the logs of the source database before the task is complete. Otherwise, the task may fail. Limits on operations on the source database: During schema migration and full data migration, do not execute DDL statements 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 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.
If the source database is a read-only instance, you cannot migrate DDL operations. In hybrid log-based parsing mode, you cannot perform multiple operations to add columns to or remove columns from the source database within 10 minutes. For example, if you execute the following SQL statements within 10 minutes, an error is reported for the task.
ALTER TABLE test_table DROP COLUMN Flag;
ALTER TABLE test_table ADD Remark nvarchar(50) not null default('');
If the source database is an ApsaraDB RDS for SQL Server instance that runs SQL Server Web edition, you must set the SQL Server Incremental Synchronization Mode parameter to Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported) when you configure the task.
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Other limits | DTS does not migrate complex DDL operations. DTS does not migrate data of the following types: CURSOR, ROWVERSION, SQL_VARIANT, HIERARCHYID, POLYGON, GEOMETRY, and GEOGRAPHY. If the number of CDC-enabled tables to be migrated in a single migration task exceeds 1,000, the precheck fails. 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 database and destination cluster. This may increase the loads on the database servers. 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 and data loss may occur. Note DTS cannot migrate DDL operations related to the primary key of a table for which CDC is enabled. If you set the SQL Server Incremental Synchronization Mode parameter to Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported) in the Select Objects step, the tables to be migrated must have clustered indexes that contain primary key columns. The tables to be migrated cannot be heap tables, tables without primary keys, compressed tables, or tables with computed columns. Ignore the preceding limits if the hybrid log-based parsing mode is used. If DDL statements fail to be executed in the destination database, the DTS task continues to run. You can view the DDL statements that fail to be executed in task logs. For more information about how to view task logs, see View task logs. If you write column names that differ only in capitalization to the same table in the destination MySQL database, the data migration result may not meet your expectations because the column names in MySQL databases are not case-sensitive. After data migration is complete, we recommend that you run the analyze table <table name> command to check whether data is written to the destination table. For example, if a high-availability (HA) switchover is triggered in the source MySQL database, data may be written only to the memory. As a result, data loss occurs. In Incremental Synchronization Based on Logs of Source Database 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 in the source database to ensure that the latency of data migration is accurate. In 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 specific tables. We recommend that you set the maximum number of records per second to 1,000 for the tables for which CDC is enabled in the source 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.
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Special cases | If the source instance is an ApsaraDB RDS for SQL Server instance, DTS automatically creates an account named rdsdt_dtsacct on the ApsaraDB RDS for SQL Server instance. This account is used for data migration. Do not delete this account or change the password of this account when your data migration task is running. Otherwise, the task may fail. For more information, see System accounts. |
Elastic Compute Service (ECS)
Container Compute Service (ACS)
icon to add the objects to the Selected Objects section. 
