enable_transfer

Description

enable_transfer specifies whether to allow Transfer operations within a tenant.

Privilege requirements

• Query the parameter

  The sys tenant and all user tenants can use the SHOW PARAMETERS statement or the GV$OB_PARAMETERS view to query this parameter.

• Modify the parameter

  The sys tenant and user tenants can modify this parameter.

Attributes

Considerations

The load balancing strategy within a tenant is jointly controlled by the enable_rebalance and enable_transfer parameters.

The enable_rebalance parameter controls whether to perform load balancing between tenants in the sys tenant and whether to perform load balancing within a tenant in a user tenant. The default value is true. After you set this parameter, you do not need to restart OBServer nodes. The setting takes effect immediately.

The enable_transfer parameter specifies whether to enable the Transfer feature within a tenant. The default value is true. After you set this parameter, you do not need to restart OBServer nodes. The setting takes effect immediately. The meaning of the value of the enable_transfer parameter depends on the value of the enable_rebalance parameter:

• If the value of the enable_rebalance parameter is false, automatic load balancing is disabled regardless of the value of the enable_transfer parameter. The following command disables all load balancing:

  obclient> ALTER SYSTEM SET enable_rebalance=false;
  

• If the value of the enable_rebalance parameter is true and the value of the enable_transfer parameter is true, the system automatically adjusts the distribution of partitions during tenant scaling operations to achieve load balancing. The following command dynamically adjusts the number of log streams based on the load balancing algorithm, automatically performs leader balancing and partition balancing within the tenant:

  obclient> ALTER SYSTEM SET enable_rebalance=true;
  obclient> ALTER SYSTEM SET enable_transfer=true;
  

• If the value of the enable_rebalance parameter is true and the value of the enable_transfer parameter is false, the system cannot initiate Transfer operations during tenant scaling operations. It can only perform limited load balancing through log stream migration. The following command performs log stream balancing based on existing log streams without initiating Transfer operations or dynamically adjusting the number of log streams:

  obclient> ALTER SYSTEM SET enable_rebalance=true;
  obclient> ALTER SYSTEM SET enable_transfer=false;
  

Examples

• Set the load balancing strategy for a specified tenant in the sys tenant.

  • Enable tenant-level load balancing and the Transfer feature within the specified tenant in the sys tenant.

    obclient> ALTER SYSTEM SET enable_rebalance = true TENANT = 'tenant_name';
    

    obclient> ALTER SYSTEM SET enable_transfer = true TENANT = 'tenant_name';
    

    The preceding statements set the values of the enable_rebalance and enable_transfer parameters to true for the specified tenant.

  • Enable tenant-level load balancing and the Transfer feature within all user tenants (excluding the sys tenant and the Meta tenant) in the sys tenant.

    obclient> ALTER SYSTEM SET enable_rebalance = true TENANT = all_user;
    

    obclient> ALTER SYSTEM SET enable_transfer = true TENANT = all_user;
    

    or

    obclient> ALTER SYSTEM SET enable_rebalance = true TENANT = all;
    

    obclient> ALTER SYSTEM SET enable_transfer = true TENANT = all;
    

    The preceding statements set the values of the enable_rebalance and enable_transfer parameters to true for all user tenants.

    Note

    Starting from V4.2.1 of OceanBase Database, the TENANT = all_user and TENANT = all clauses have the same semantics. When you want to apply the settings to all user tenants, we recommend that you use the TENANT = all_user clause. The TENANT = all clause will be deprecated in the future.

• Set the load balancing strategy for the current tenant in a user tenant.

  MySQL-compatible mode

  Oracle-compatible mode

  The following statements enable tenant-level load balancing and the Transfer feature within the current MySQL-compatible tenant:

  obclient> ALTER SYSTEM SET enable_rebalance = true;
  

  obclient> ALTER SYSTEM SET enable_transfer = true;
  

  The following statements enable tenant-level load balancing and the Transfer feature within the current Oracle-compatible tenant:

  obclient> ALTER SYSTEM SET enable_rebalance = 'true';
  

  obclient> ALTER SYSTEM SET enable_transfer = 'true';
  

References

• Scale in or out a tenant by adjusting the number of units
• Scale in or out a tenant by adjusting the primary zone
• enable_rebalance