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 source 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.
Precautions
- DTS uses read and write resources of the source and destination databases during initial full data synchronization. This may increase the loads of the database servers. 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 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. For example, you can synchronize data when the CPU utilization of the source and destination databases is less than 30%.
- When the data synchronization task is running, do not upgrade or downgrade the DRDS instance, migrate frequently-accessed tables, change shard keys, or perform DDL operations on source objects. Otherwise, the data synchronization task fails.
- If you switch the network type of the DRDS instance during data synchronization, you must submit a ticket to update the network connection settings of the data synchronization task.
SQL operations that can be synchronized
INSERT, UPDATE, and DELETE
Before you begin
DTS does not support schema synchronization between DRDS instances. Therefore, you must create a database and tables in the destination DRDS instance based on the schemas of the objects in the source DRDS instance. For more information, see Create a DRDS database and Create a DRDS table.
Note During
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 This parameter is set to DRDS Instance and cannot be changed. Instance Region 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 This parameter is set to DRDS Instance and cannot be changed. Instance Region 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. - Select the synchronization policy and the objects to be synchronized.
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, only some 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.
- By default, 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 rename the objects that are synchronized to the destination instance. For more information, see Rename an object to be synchronized.
- 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, DTS performs a precheck. The data synchronization task can be started only after it passes the precheck.
- If the task fails to pass the precheck, you can click the
icon next to each failed item to view details.
- You can troubleshoot the issues based on the causes and run a precheck again.
- If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.
- Wait until the initial synchronization is complete and the data synchronization task is in the Synchronizing state.
You can view the status of the data synchronization task on the Synchronization Tasks page.
