Distributed Relational Database Service (DRDS) is developed by Alibaba Group to address the bottleneck of single-host database services. DRDS is compatible with the MySQL protocol and syntax, and supports automatic sharding, online smooth scaling, auto scaling, and transparent read/write splitting. DRDS provides O&M capabilities throughout the lifecycle of databases. This topic describes how to synchronize data between DRDS instances by using Data Transmission Service (DTS).
Prerequisites
- The MySQL version of the source and destination DRDS instance is MySQL 5.
- The databases is created in the DRDS instance based on one or more ApsaraDB RDS for MySQL instances that you purchased.
- The tables to be synchronized contain primary keys.
- The destination database in the RDS instance that corresponds to the destination DRDS instance has sufficient storage space.
Precautions
- DTS uses read and write resources of the source and destination databases during initial full data synchronization. This may increase the database load. If the database performance is unfavorable, the specification is low, or the data volume is large, database services may become unavailable. For example, DTS occupies a large amount of read and write resources in the following cases: a large number of slow SQL queries are performed on the source database, the tables have no primary keys, or a deadlock occurs in the destination database. Before synchronizing data, you must evaluate the performance of the source and destination databases. We recommend that you synchronize data during off-peak hours. For example, you can synchronize data when the CPU usage of the source and destination databases is less than 30%.
- We recommend that you do not perform operations such as scale-out, migration hot spot table , change shard key, and change DDL during data synchronization. Otherwise, data synchronization may fail.
- After you change the network type of a DRDS instance during data synchronization, you must submit a ticket to modify the network connection information of the synchronization channel.
SQL operations that can be synchronized
INSERT, UPDATE, and DELETE
Preparations
Create a database and tables in the destination DRDS instance based on the schemas of the objects in the source DRDS instance. This is because DTS does not support initial schema synchronization between DRDS instances. For more information, see Create a DRDS database and Create a DRDS table.
Note Initial schema synchronization: DTS synchronizes the schemas of the required objects from the source database to
the destination database.
Procedure
- At the top of the Synchronization Tasks page, select the region where the destination instance resides.
- Configure the source and destination instances.
Section Parameter Description N/A Synchronization Task Name DTS automatically generates a task name. We recommend that you specify an informative name for easy identification. You do not need to use a unique task name. Source Instance Details Instance Type The value of this parameter is set to DRDS and cannot be changed. Instance Region The region of the source instance. The region is the same as the source region that you selected when you purchased the data synchronization instance. You cannot change the value of this parameter. DRDS Instance ID Select the ID of the source DRDS instance. Destination Instance Details Instance Type The value of this parameter is set to DRDS and cannot be changed. Instance Region The region of the destination instance. The region is the same as the destination region that you selected when you purchased the data synchronization instance. You cannot change the value of this parameter. DRDS Instance ID Select the ID of the destination DRDS instance. - Configure the synchronization policy and objects.
Parameter Description Processing Mode In Existed Target Table - Pre-check and Intercept: checks whether the destination tables are empty. If the destination tables are empty, the precheck is passed. If the tables are not empty, an error is returned during the precheck and the data synchronization task cannot be started.
- Ignore: skips the check for empty destination tables.
Warning If you select Ignore, data consistency is not guaranteed and your business may be exposed to potential risks.
- If the source and destination databases have the same schema, DTS does not synchronize data records that have the same primary keys as data records in the destination database.
- If the source and destination databases have different schemas, initial data synchronization may fail. In this case, only some columns are synchronized or the data synchronization task fails.
Objects to be synchronized Select tables from the Available section and click the
icon to move the tables to the Selected section.
Note- You can select only tables as the objects to be synchronized.
- After an object is synchronized to the destination database, the name of the object remains unchanged. You can change the name of an object in the destination instance by using the object name mapping feature provided by DTS. For more information about how to use this feature, see Specify the name of an object in the destination instance.
- In the lower-right corner of the page, click Precheck.
Note
- Before you can start the data synchronization task, a precheck is performed. You can start the data synchronization task only after the task passes the precheck.
- If the task fails to pass the precheck, click the
icon next to each failed item to view details. Troubleshoot the issues based on the
causes and run the precheck again.
- Wait until the initial synchronization is complete and the data synchronization task
is in the Synchronizing state.
On the Synchronization Tasks page, view the status of the data synchronization task.
icon to move the tables to the 
icon next to each failed item to view details. Troubleshoot the issues based on the
causes and run the precheck again.
