This topic introduces the limitations of the physical standby database feature.
| Limitation | Description |
|---|---|
| Maximum number of standby tenants supported by one primary tenant | Unlimited |
| Requirement for the primary and standby tenants to have homogeneous resources | Not required. It is recommended for the primary and standby tenants to use the same resource specifications. |
| Parameters | Parameters of the primary and standby tenants are independent and not physically synchronized. If you modify a parameter of the primary tenant, evaluate whether the same parameter of the standby tenant needs to be modified as well. |
| System variables | System variables of the primary and standby tenants are physically synchronized. If a system variable of the primary tenant is modified, the system will synchronize the same system variable on the standby tenants. |
| Users and user passwords | Creating users and changing user passwords are only supported on the primary tenant. The updated information will be synchronized to the standby tenants. |
| Read/write operations | Read operations are supported on the standby tenants, while write operations are not supported. |
| Minor and major compactions | Minor compactions of the primary and standby tenants are independent. The standby tenant synchronizes major compaction information from the primary tenant and does not support independent major compaction. |
| Switchover limitation | All replicas of the log streams on the standby tenant must be online. |
| Failover limitation | All replicas of the log streams on the standby tenant must be online. |
| Optimizer statistics | The standby tenant does not collect statistics. Statistics are synchronized from the primary tenant to the standby tenant. |