PolarDB:Add and manage a secondary cluster

Pricing

When you use a GDN, you are charged for the clusters and any inter-region data transfer fees. Data transfer fees vary based on whether the transfer is cross-border.

• Non-cross-border data transfer (Free)

  • Scenario: The primary and secondary clusters are both deployed in regions outside the Chinese mainland, or both are deployed in regions within the Chinese mainland.

  • Billing rule: Free.

• Cross-border data transfer (Billable)

  Important

  Cross-border data transfer fees will be charged starting from 00:00 on January 1, 2026 (Singapore time). Before this date, this service is free.

  • Scenario: One of your clusters (primary or secondary) is deployed in a region outside the Chinese mainland, and the other is deployed in a region in the Chinese mainland.

  • Billing rule: USD 0.80 per GB, billed hourly. The fee is calculated based on the amount of Redo Log data that is physically replicated from the primary cluster to a cross-border secondary cluster within one hour. You can estimate this traffic fee by querying the physical position converted from the log sequence number (LSN).

    Click to view a billing example

    Example

    For example, at 09:00, you query the physical write position of the log and it is ib_logfile1/648143676. At 10:00, the position is updated to ib_logfile3/648142342. This indicates that the amount of data written in this hour is the difference between the two positions.

    1. Amount written to the start file (ib_logfile1):
       Subtract the start offset from the total file size. Each log file is 1 GB (1,073,741,824 bytes). The amount written is 1073741824 - 648143676 = 425598148 bytes.

    2. Amount written to the intermediate file (ib_logfile2):
       After ib_logfile1 is full, the system completely writes ib_logfile2. This amount is 1,073,741,824 bytes (1 GB).

    3. Amount written to the end file (ib_logfile3):
       This is the offset at the end, which is 648142342 bytes.

    Therefore, the total amount written = 425598148 + 1073741824 + 648142342 = 2147482314 bytes. This is 2147482314 / 1024 / 1024 / 1024 = 1.999998 GB (rounded down to six decimal places). The cross-border data transfer fee for this hour is approximately 1.999998 GB × USD 0.80/GB = USD 1.5999984.

    Query the log write progress and physical file offset

    -- Query the current write progress of the log system.
    SHOW STATUS LIKE 'Innodb_log_write_lsn'; 
    +----------------------+------------+
    | Variable_name        | Value      |
    +----------------------+------------+
    | Innodb_log_write_lsn | 1721889596 |
    +----------------------+------------+
    
    -- Query the physical file offset in bytes.
    SELECT lsn_to_pos(1721889596); 
    +------------------------+
    | lsn_to_pos(1721889596) |
    +------------------------+
    | ib_logfile1/648143676  |
    +------------------------+

Usage notes

A GDN synchronizes data using a physical replication mechanism that is based on redo logs. Therefore, you do not need to enable binary logging by default. If you have specific business requirements, such as change tracking, and want to synchronize binary logs (binlogs) between clusters, ensure that the binlog parameter (loose_polar_log_bin) is identical for the primary and secondary clusters. Otherwise, if you switch the primary cluster, data inconsistency may occur in the binlogs.

Add a secondary cluster

A GDN supports adding cross-border secondary clusters using China Unicom's cross-border Express Connect and Cloud Enterprise Network (CEN). A configuration is considered cross-border if the primary and secondary clusters are in different types of regions, as described below. Adding a cross-border secondary cluster requires additional preparation.

• Chinese mainland: China (Hangzhou), China (Shanghai), China (Shenzhen), China (Heyuan), China (Guangzhou), China (Qingdao), China (Beijing), China (Zhangjiakou), China (Hohhot), China (Ulanqab), and China (Chengdu).

• Other regions: China (Hong Kong), Japan (Tokyo), South Korea (Seoul), Singapore, Malaysia (Kuala Lumpur), Indonesia (Jakarta), Philippines (Manila), Thailand (Bangkok), Germany (Frankfurt), US (Silicon Valley), US (Virginia), and UK (London).

Remove a secondary cluster

1. Log on to the PolarDB console. In the navigation pane on the left, click Global Database Network.

2. On the GDN page, find the target GDN and click its GDN ID/Name to go to the details page.

3. In the Clusters section, find the target secondary cluster and click Remove in the Actions column.

   Note

   • The removal process takes about 5 minutes.

   • During the removal process, the endpoints of all clusters in the GDN, including the secondary cluster that is being removed, remain available. You can continue to access the databases using the cluster endpoints.

   • Only secondary clusters can be removed from a GDN. The primary cluster cannot be removed.

   • After a secondary cluster is removed from a GDN, it stops synchronizing data from the primary cluster and is set to read/write mode.

   • After a secondary cluster is removed from a GDN, it cannot be added back to the GDN as a secondary cluster. Perform this operation with caution.

4. In the dialog box that appears, read the notes, and then click OK to remove the secondary cluster.

Switch the primary cluster

1. Log on to the PolarDB console. In the navigation pane on the left, click Global Database Network.

2. On the GDN page, find the target GDN and click its GDN ID/Name to go to the details page.

3. In the Clusters section, find the target secondary cluster and click Switch to Primary Cluster in the Actions column.

4. In the Primary/Secondary Switchover dialog box, select the ID of the secondary cluster that you want to promote to the primary cluster, and then click OK.

   Note

   • A primary/secondary switchover does not swap the connection addresses of the two clusters. You must reconfigure your application. If the original primary cluster has a public endpoint, you must ensure that the new primary cluster also has a public endpoint. Otherwise, your application cannot access the database. For more information, see View endpoints and ports.

   • A primary/secondary switchover in a GDN is typically completed in less than 5 minutes, but can take up to 10 minutes. During the switchover, a transient disconnection of up to 160 seconds may occur. We recommend that you perform the switchover during off-peak hours and make sure that your application has a reconnection mechanism.

   • If you enable the Forced Switchover switch in the Primary/Secondary Switchover dialog box:

     • You cannot specify a target cluster for a forced switchover. By default, the secondary cluster with the largest log sequence number (LSN) is promoted to the new primary cluster.

     • A forced switchover may cause data loss. After the switchover, the original primary cluster is automatically removed from the GDN. Perform this operation with caution.

Recreate a secondary cluster

FAQ

References

• Connect to a global database network: Describes how to connect to a global database network (GDN).

• Create a global domain name: Describes how to create a unified endpoint that provides nearest access and remains unchanged after a primary cluster switchover.

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