Modify a unit config

You can increase or decrease the CPU, memory, and log disk capacities in a unit config.

Considerations

To increase the capacities of a unit config corresponding to resource units that are being used by a tenant, make sure that each node has sufficient free resources. You can query the oceanbase.GV$OB_SERVERS view for the total resources and allocated resources on each node to determine whether a unit config can be modified.

To increase the capacities of a unit config, make sure that the capacities after the increase meet the following requirements:

Sum(min_cpu) <= CPU_CAPACITY;
Sum(max_cpu) <= CPU_CAPACITY * resource_hard_limit;
Sum(memory_size) <= MEM_CAPACITY;
Sum(log_disk_size) <= LOG_DISK_CAPACITY;

where:

• CPU_CAPACITY indicates the total CPU capacity on a single node.

• MEM_CAPACITY indicates the total memory capacity on a single node.

• LOG_DISK_CAPACITY indicates the total log disk capacity on a single node.

  The total capacity of the log disk is jointly controlled by the cluster-level parameters log_disk_size and log_disk_percentage. The log_disk_size parameter specifies the size of the log disk space for storing REDO logs, and its default value is 0. The log_disk_percentage parameter specifies the percentage of the log disk space for storing REDO logs, and its default value is 0. Rules for using the two parameters are as follows:

  • If the value of log_disk_size is 0M and that of log_disk_percentage is not 0, the system allocates the space of the log disk based on the value of log_disk_percentage.

  • If the value of log_disk_size is not 0M, the system allocates the space of the log disk based on the value of log_disk_size regardless of whether the value of log_disk_percentage is 0.

  • If the value of log_disk_size is 0M and that of log_disk_percentage is 0, the system calculates the percentage of the disk space occupied by REDO logs based on whether logs and data are stored on the same disk.

    • If the disk is shared, the percentage of the disk space occupied by REDO logs is 30%.

    • If the disk is exclusive for REDO logs, the percentage of the disk space occupied by REDO logs is 90%.

  For more information about the log_disk_size parameter, see log_disk_size.

  For more information about the log_disk_percentage parameter, see log_disk_percentage.

• resource_hard_limit indicates a specific system parameter.

  The system allocates CPU resources based on the value of the resource_hard_limit parameter. The value range is [100, 10000]. The default value is 100, indicating that overprovisioning is not allowed.

  For more information about the resource_hard_limit parameter, see resource_hard_limit.

Before you downgrade a unit config, make sure that the total CPU, memory, and log disk capacity after the downgrade is greater than or equal to the current size of used space of the log disk.

Limitations

You can modify a unit config only in the sys tenant.

Procedure

You can modify the CPU, memory, input/output operations per second (IOPS), and log disk capacities of a unit config. If you do not specify a new value for an item, the original value of the item takes effect.

1. Log on to the sys tenant of the cluster as the root user.

2. Modify a unit config.

   Here is a sample statement:

   ALTER RESOURCE UNIT unitname
   MAX_CPU [=] cpunum,
   [MIN_CPU [=] cpunum,]
   MEMORY_SIZE [=] memsize,
   [MAX_IOPS [=] iopsnum, MIN_IOPS [=] iopsnum,IOPS_WEIGHT [=]iopsweight,]
   [LOG_DISK_SIZE [=] logdisksize];
   

   Execute the following statement to modify the configurations of the unit1 resource unit:

   obclient> ALTER RESOURCE UNIT unit1 MAX_CPU 15, MEMORY_SIZE '20G', LOG_DISK_SIZE '4G';