This topic describes the precautions and limits when you migrate data from an SQL Server database, such as a self-managed SQL Server database or an ApsaraDB RDS for SQL Server database. To ensure that your data migration task runs as expected, read the precautions and limits before you configure the task.

Scenarios of migrating data from an SQL Server database

The following list provides the scenarios of migrating data from an SQL Server database. The precautions and limits in the scenarios may vary. You can go to the related section to view the precautions and limits in a specific scenario.

Migrate data between SQL Server databases

Category Description
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 database.
  • 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 are met:
    • 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 later.
    • 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.
Other limits
  • 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 is used.
  • 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 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.
  • 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.
Special cases 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.

Migrate data from an SQL Server database to an AnalyticDB for MySQL cluster

Category Description
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 database.
  • 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 are met:
    • 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 later.
    • 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.
Other limits
  • DTS does not migrate data of the following types: TIMESTAMP, CURSOR, ROWVERSION, HIERACHYID, SQL_VARIANT, SPATIAL GEOMETRY, SPATIAL GEOGRAPHY, and TABLE.
  • 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 is used.
  • 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.
  • Due to the limits of AnalyticDB for MySQL clusters, if the disk space usage of the nodes in an AnalyticDB for MySQL cluster reaches 80%, the performance of data writing to the destination database is compromised and the DTS task is delayed. If the usage reaches 90%, data cannot be written to the destination database and error messages are returned. We recommend that you estimate the required disk space based on the objects to be migrated. 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 the read and write resources of the source and destination databases. This may increase the loads on 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.
  • 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.

Migrate data from an SQL Server database to an AnalyticDB for PostgreSQL instance

Category Description
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 database.
  • 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 are met:
    • 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 later.
    • 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.
Other limits
  • DTS does not migrate data of the following types: TIMESTAMP, CURSOR, ROWVERSION, HIERACHYID, SQL_VARIANT, SPATIAL GEOMETRY, SPATIAL GEOGRAPHY, and TABLE.
  • 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 is used.
  • 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 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.
  • 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.