|Limits on the source database
- The tables to be synchronized must have PRIMARY KEY or UNIQUE constraints and all
fields must be unique. Otherwise, the destination database may contain duplicate data
- If you select tables as the objects to be synchronized and you need to edit tables
(such as rename tables or columns), up to 1,000 tables can be synchronized in a single
data synchronization task. If you run a task to synchronize more than 1,000 tables,
a request error occurs. In this case, we recommend that you split the tables to be
synchronized, configure multiple tasks to synchronize the tables, or call DTS API
operations to configure tasks.
- The following requirements for data logs must be met:
- The data logging feature must be enabled. The backup mode must be set to Full, and
full logical backup must be performed.
- Data logs are retained for at least 7 days during full data synchronization. You can
wait until full data synchronization is complete, and then clear the data logs generated
in the source database after the DTS task is run.
Note To ensure data security, the DTS server stores only 50 GB of data logs or the data
logs for the last 24 hours. If the limit is exceeded, the DTS server automatically
clears the cached logs.
Warning If you clear the data logs of the source database during full data synchronization,
the data synchronization task may fail. For example, full data synchronization takes
more than 24 hours due to the large data volume in the source database and abnormal
writing in the destination database. In this case, if the data logs of the source
database are cleared during full data synchronization, DTS cannot obtain the data
logs generated 24 hours ago. Therefore, the data synchronization task may fail.
- Requirements for the objects to be synchronized:
- DTS supports schema synchronization for the following types of objects: schema, table,
view, function, and procedure.
SQL Server and AnalyticDB for MySQL are heterogeneous databases. Their data types
do not have one-to-one correspondence. We recommend that you evaluate the impact of
data type conversion on your business. For more information, see Data type mappings for schema synchronization
- DTS does not synchronize the schemas of assemblies, service brokers, full-text indexes,
full-text catalogs, distributed schemas, distributed functions, CLR stored procedures,
CLR scalar-valued functions, CLR table-valued functions, internal tables, systems,
or aggregate functions.
- DTS does not synchronize data of the following types: TIMESTAMP, CURSOR, ROWVERSION,
HIERACHYID, SQL_VARIANT, SPATIAL GEOMETRY, SPATIAL GEOGRAPHY, and TABLE.
- DTS does not synchronize tables that contain computed columns.
- If you set SQL Server Incremental Synchronization Mode to Incremental Synchronization Based on Logs of Source Database in the Configure Objects and Advanced Settings step, the tables to be synchronized must have clustered indexes that contain primary
- To ensure that the latency of data synchronization is accurate, DTS adds a heartbeat
table to the source database. The name of the heartbeat table is dts_log_heart_beat.
- 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 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 that you want to synchronize.
You must ensure that the destination cluster has sufficient storage space.
- Before you synchronize data, evaluate the impact of data synchronization on the performance
of the source and destination databases. We recommend that you synchronize data during
off-peak hours. During full data synchronization, DTS uses read and write resources
of the source and destination databases. This may increase the loads of the database
- During full data synchronization, concurrent INSERT operations cause fragmentation
in the tables of the destination database. After full data synchronization is complete,
the tablespace of the destination database is larger than that of the source database.
- We recommend that you do not use gh-ost or pt-online-schema-change to perform data
definition language (DDL) operations on source tables during data synchronization.
Otherwise, data synchronization may fail.