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Resource groups

Written by
Updated at December 4, 2024

By using resource groups, users with the mdb_admin role can set quotas for the following resources allocated for query processing:

  • CPU computing resources
  • Amount of RAM
  • Number of concurrent transactions

A resource group may include several roles that will share their quotas.

Greenplum® gets a transaction query from the user and matches its resource requirements with the unused quotas in the resource group. If the quotas are sufficient, the query execution begins immediately. If not, the query waits for other queries to be completed and to free up the resources. Queries are queued based on the first in, first out (FIFO) principle.

Resource group parameters

Every resource group has the following parameters:

Name Description
MEMORY_AUDITOR The memory auditor used by the resource group. Managed Service for Greenplum® uses vmtracker as the default value.
CONCURRENCY The maximum number of concurrent transactions a resource group can process. Both active and pending transactions are counted. The default value is 20.
CPU_RATE_LIMIT The percentage of CPU resources allocated to the segment. The minimum value is 1; the maximum value is 100. The value is automatically reset to -1 if the CPUSET parameter is specified.
CPUSET The numbers of allocated CPU cores. The numbers or intervals are enclosed in quotes, e.g., '1,3-4'. Use the numbers that exist in the system and are not allocated to other resource groups. The value is automatically reset to -1 if the CPU_RATE_LIMIT parameter is specified.
MEMORY_LIMIT The percentage of RAM reserved for the segment. The minimum value is 0 (default); the maximum value is 100. When the value is 0, the resource group can only use non-allocated RAM to run queries. The total MEMORY_LIMIT value for all resource groups may not exceed 100.
MEMORY_SHARED_QUOTA The allocated memory percentage (MEMORY_LIMIT) that can be used by all the resource group transactions as needed. The minimum value is 1; the maximum value is 100. The default value is 80. For more information, see Memory allocation.
MEMORY_SPILL_RATIO The RAM usage threshold per transaction operator. When this threshold is reached, temporary files are created on the disk to process the operator. The minimum value is 0 (default); the maximum value is 100. If MEMORY_LIMIT is 0, this parameter must also equal 0.

Default resource groups

Once you create a Managed Service for Greenplum® cluster, it includes three resource groups:

  • admin_group: Service group assigned to the monitor and gpadmin service roles.

  • mdb_admin_group: Group for administrators. By default, it is assigned to the administrator user whose username and password you specified when creating the cluster.

    If the administrator and other users belong to the same resource group, and all its resources are used up, the administrator will not be able to connect to the database and interrupt resource-intensive processes manually. This is why we recommend assigning this resource group only to the users with the mdb_admin role.

  • default_group: Shared group. It is assigned to a newly created role unless it is assigned another explicit resource group.

Default values of the resource group parameters:

Parameter admin_group mdb_admin_group default_group
MEMORY_AUDITOR vmtracker vmtracker vmtracker
CONCURRENCY 10 20 20
CPU_RATE_LIMIT 10 1 30
CPUSET -1 -1 -1
MEMORY_LIMIT 10 0 0
MEMORY_SHARED_QUOTA 80 80 80
MEMORY_SPILL_RATIO 0 0 0

You cannot change the values of the admin_group resource group.

For more information about managing roles, see Users and roles and the Greenplum® documentation.

Memory allocation

  • You can allocate a segment's RAM share for each resource group using the MEMORY_LIMIT parameter. This percentage is split into the shared quota and guaranteed quota:

    • The shared quota is set in the MEMORY_SHARED_QUOTA parameter and can be used by all the resource group transactions. Greenplum® distributes the shared quota to transactions based on the first in, first out principle.

    • The guaranteed quota is allocated to each transaction and calculated by the following formula:

      (MEMORY_LIMIT − MEMORY_SHARED_QUOTA)/CONCURRENCY

  • If the total of MEMORY_LIMIT values of all resource groups is below 100, Greenplum® distributes unallocated RAM to any transactions from any resource groups based on the first in, first out principle.

    The transaction uses non-allocated memory when both conditions are met:

    • The guaranteed memory share for the transaction is used up.
    • The shared quota for the resource group is used up.

    For your cluster to run in a stable and efficient manner, leave 10% to 20% of memory unallocated.

CPU resource allocation

There are two ways to allocate CPU resources for a resource group:

  • (Recommended) Specify the share of the segment's CPU resources that will be available to the resource group (CPU_RATE_LIMIT parameter).

    Managed Service for Greenplum® has a management mode that re-allocates CPU resources from idle resource groups to highly loaded ones. When a resource group is not idle anymore, it regains its re-allocated CPU resources.

  • Specify the CPU core numbers to be used by the resource group in the CPUSET parameter. These cores will not be available to other resource groups. When the resource group is not processing any transactions, the cores allocated to it become idle. We recommend you to minimize the number of such resource groups.

    For stable cluster operation, we do not recommend allocating the core numbered 0.

You can use these two methods at the same time, for different resource groups, or switch them over as you run your cluster.

To learn more about resource groups, see the Greenplum® documentation.

Greenplum® and Greenplum Database® are registered trademarks or trademarks of VMware, Inc. in the United States and/or other countries.

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