Distributed Relational Database Service (PolarDB-X 1.0) 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 from a PolarDB for MySQL cluster to a PolarDB-X 1.0 instance by using Data Transmission Service (DTS).
Prerequisites
- The binary logging feature is enabled for the PolarDB for MySQL cluster. For more information, see Enable binary logging.
- The tables to be synchronized from the source database contain primary keys.
- The destination database has sufficient storage space.
- A PolarDB-X 1.0 instance is created. For more information, see Step 1: Create a instance and Step 2: Create a database.
Note When you create an instance, you must select RDS MySQL as the storage type.
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%.
- During initial full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination cluster. After initial full data synchronization, the tablespace of the destination cluster is larger than that of the source database. You must make sure that the destination database has sufficient storage space.
- DTS does not synchronize schemas from an ApsaraDB RDS for MySQL instance to a PolarDB-X 1.0 instance. Before you configure a data synchronization task, you must create databases and tables in the destination instance.
Limits
- You can select only tables as the objects to be synchronized.
- DTS does not synchronize the following types of data: BIT, VARBIT, GEOMETRY, ARRAY, UUID, TSQUERY, TSVECTOR, and TXID_SNAPSHOT.
- Prefix indexes cannot be synchronized. If the source database contains prefix indexes, data may fail to be synchronized.
- We recommend that you do not use gh-ost or pt-online-schema-change to perform DDL operations on objects during data synchronization. Otherwise, data synchronization may fail.
SQL operations that can be synchronized
INSERT, UPDATE, and DELETE
Permissions required for database accounts
| Database | Required permissions |
|---|---|
| PolarDB for MySQL | The database account must have the SELECT permission on the objects to be synchronized, the REPLICATION CLIENT permission, the REPLICATION SLAVE permission, and the SHOW VIEW permission. |
| PolarDB-X 1.0 | DTS automatically creates a database account and grants permissions to the account. You do not need to specify the database account. |
Supported synchronization topologies
- One-way one-to-one synchronization
- One-way many-to-one synchronization
Supported synchronization topologies
- One-way one-to-one synchronization
- One-way many-to-one synchronization
Before you begin
When you synchronize data from a PolarDB for MySQL cluster to a PolarDB-X 1.0 instance, note that DTS does not support initial schema synchronization. Therefore, you must create databases and tables in the destination instance based on the schemas of the objects in the source PolarDB for MySQL cluster. 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
- Configure the source cluster and the destination instance.
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 Select PolarDB Instance. Instance Region The source region that you selected on the buy page. You cannot change the value of this parameter. PolarDB Instance ID Select the ID of the source PolarDB cluster. Database Account Enter the database account of the source PolarDB cluster. For information about the permissions that are required for the account, see Permissions required for database accounts. Database Password Enter the password of the database account. 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 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 change the names of the objects that are synchronized to the destination instance. For more information, see Rename an object to be synchronized.
Rename Databases and Tables You can use the object name mapping feature to rename the objects that are synchronized to the destination instance. For more information, see Object name mapping.
Retry Time for Failed Connections By default, if DTS fails to connect to the source or destination database, DTS retries within the next 720 minutes (12 hours). You can specify the retry time based on your needs. If DTS reconnects to the source and destination databases within the specified time, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails.Note When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time based on your business needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released. - 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. You can start the data synchronization task only after the task 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.
