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
- A database is created in the DRDS instance based on one or more ApsaraDB RDS for MySQL
instances.
- 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.
Limits
- 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 scale up or down the DRDS instance, migrate frequently-accessed
tables, change shard keys, or perform DDL operations on objects during data synchronization.
Otherwise, data synchronization may fail.
- If you need to change the network type of a DRDS instance during data synchronization,
you must submit a ticket to modify the network connection information.
SQL operations that can be synchronized
INSERT, UPDATE, and DELETE
Before you begin
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 During initial schema synchronization, DTS synchronizes the schemas of the required objects from the source database to
the destination database.
Procedure
- Purchase a data synchronization instance. For more information, see Purchase procedure.
Note On the buy page, set both Source Instance and Target Instance to DRDS and set Synchronization Topology to One-Way Synchronization.
- Log on to the DTS console.
- In the left-side navigation pane, click Data Synchronization.
- At the top of the Synchronization Tasks page, select the region where the destination instance resides.
- Find the data synchronization instance and click Configure Synchronization Channel in the Actions column.
- 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 on the buy page. 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 on the buy page. You cannot change the value of this parameter.
|
DRDS Instance ID |
Select the ID of the destination DRDS instance. |
- In the lower-right corner of the page, click Set Whitelist and Next.
Note In this step, DTS adds the CIDR blocks of DTS servers to the whitelists of the source
and destination DRDS instances. This ensures that DTS servers can connect to the DRDS
instances.
- Configure the synchronization policy and objects.

Setting |
Description |
Select the processing mode of conflicting tables |
- 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
the data records that have the same primary keys as the data records in the destination
database.
- If the source and destination databases have different schemas, initial data synchronization
may fail. In this case, only specific columns are synchronized or the data synchronization
task fails.
|
Select the objects to be synchronized |
Select one or more 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 instance, the name of the object
remains unchanged. You can use the object name mapping feature to change the names
of the objects that are synchronized to the destination instance. For more information,
see Specify the name of an object in the destination instance.
|
- Click Next.
- Specify whether you want to perform initial full data synchronization.

Note During initial full data synchronization, DTS synchronizes the historical data of the required objects from the source database
to the destination database. If you do not select Initial Full Data Synchronization,
DTS does not synchronize the historical data.
- 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.
- Close the Precheck dialog box after the following message is displayed: The precheck is passed.
- 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.
