A global database network (GDN) consists of multiple PolarDB clusters that are deployed in multiple regions worldwide. This topic describes the details about GDNs.

Data is synchronized among all clusters in a GDN. All clusters in a GDN accept read and write requests. GDNs support geo-disaster recovery. You can use a GDN to meet your business requirements in the following scenarios:
  • Active geo-redundancy

    In most scenarios, databases are deployed in the primary region. If you deploy your applications in multiple regions and deploy databases in the primary region, the applications that are not deployed in the primary region must be granted access to the databases in the primary region. This can cause network latency and reduce the performance of your service. A GDN supports data synchronization across regions at a low latency and cross-region read/write splitting. In a GDN, an application can read data from the clusters in the same region. This way, the applications in all regions can access the databases at a latency of less than 2 seconds.

  • Geo-disaster recovery
    GDNs support geo-disaster recovery regardless of whether your applications are deployed in one or more regions. If the region where the primary cluster is deployed fails to provide services, you must switch your service to a secondary cluster.
    Note The maximum time required for a failover to be completed is 10 minutes. Test results based on real business scenarios show that a failover can be completed within 5 minutes. During the failover, a transient connection of approximately 60 seconds can occur. We recommend that you perform this operation during off-peak hours and make sure that your applications can automatically reconnect to the database service.
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Request routing

The read and write requests on each cluster in a GDN are routed based on the cluster endpoint configuration. For example, Cluster 1 is the primary cluster, and Cluster 2 and Cluster 3 are secondary clusters. If the endpoint of Cluster 2 is configured to process both read and write requests and the primary node of Cluster 2 accept read requests, read requests are routed to the primary node of the primary cluster. In this case, the request latency can be high. If the endpoint of Cluster 3 is configured to process only read requests, read requests are routed only to the read-only nodes of the secondary clusters. For more information about how to configure the endpoint of a cluster, see Configure the PolarDB proxy.
Note If the endpoint of a secondary cluster is configured to process both read and write requests, write requests are routed to the primary node of the primary cluster. If session consistency is enabled for a secondary cluster, read requests on the cluster can be routed to the primary node of the primary cluster.

Benefits

  • If an application is deployed in one region, you can deploy it in multiple regions without modifying the business code. For more information, see Cross-region deployment.
  • Cross-region read/write splitting is supported. Each cluster in a GDN can process both read and write requests. Read requests are sent to the cluster in the same region. Write requests are forwarded to the primary cluster. For more information, see Cross-region read/write splitting.
  • Flexible configuration is supported. The primary cluster and secondary clusters can be configured separately. The configuration of a cluster includes cluster specifications, whitelists, and parameter values. For more information, see Create a GDN.
  • Data of clusters in different regions can be synchronized at a low latency. Physical replication is performed by using multiple channels. A large volume of data can be synchronized worldwide at a latency of less than 2 seconds. For more information, see Low-latency synchronization across regions.

Fees

You are not charged for the traffic that is generated by cross-region data transmission within a GDN. You are charged for PolarDB clusters in the GDN. For more information about the pricing rules of PolarDB clusters, see Billable items.

Supported regions and clusters

  • Regions: GDNs are available in more than 10 regions, including regions inside mainland China, the China (Hong Kong) region, and regions outside China.
  • Clusters in a GDN must meet the following requirements:
    • The cluster edition must be Cluster Edition.
    • The cluster version must be V8.0 of the ApsaraDB PolarDB MySQL-compatible edition.

Get started with GDNs

For more information, see Create a GDN.

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GDN

References