Note
- For V4.4.x, this parameter is available starting with V4.4.2.
- For V4.2.5, this parameter is available starting with V4.2.5 BP5.
Description
zone_deploy_mode specifies the distribution mode of a tenant across zones.
Privilege requirements
Query the parameter
The
systenant and all user tenants can use theSHOW PARAMETERSstatement or theGV$OB_PARAMETERSview to query this parameter.Modify the parameter
The
systenant and user tenants can modify this parameter.
Attributes
| Attribute | Description |
|---|---|
| Parameter type | String |
| Default value | homo |
| Value range |
|
| Modifiable | Yes. You can use the ALTER SYSTEM SET statement to modify the parameter. |
| Effective upon OBServer node restart | No |
Considerations
By default, a newly created tenant or an upgraded existing tenant uses the homogeneous zone mode. In the homogeneous zone mode, the number of units in each zone is the same, and the log streams are symmetrically distributed across zones. The log streams are bound to unit groups:
A unit group consists of one unit from each zone. Each unit belongs to only one unit group.
A log stream belongs to only one unit group, and its replicas are distributed across the units in that unit group.
You can scale the number of units only at the unit group level. The
UNIT_NUMvalue of each zone must be adjusted to ensure consistency.
To enable the heterogeneous zone mode, set the zone_deploy_mode parameter to hetero. After this setting, you cannot change the value of the zone_deploy_mode parameter back to homo.
Compared with the homogeneous zone mode, the heterogeneous zone mode has the following differences:
The concept of unit groups no longer applies to log stream distribution. The replicas of log streams are no longer restricted to symmetric units across zones.
The
UNIT_NUMvalues of resource pools can be different. However, at most two differentUNIT_NUMvalues can exist.You can modify the
UNIT_NUMvalue of a specific resource pool to scale resources at the resource pool level.When you use the
ALTER RESOURCE TENANTstatement to reduce the number of units, you cannot specify theUNIT_GROUPparameter to delete units.When you use the
ALTER SYSTEM CREATE LSandALTER SYSTEM MODIFY LSstatements to manage log streams, you cannot specify theUNIT_GROUPparameter.
Examples
Set the distribution mode of a tenant across zones to heterogeneous zone mode.
obclient> ALTER SYSTEM SET zone_deploy_mode = 'hetero';