Resource Classes for Shared Memory Allocation

This feature enables the Database Server Administrator (DBSA) to partition among databases the shared memory that is available to PDQ queries, so that memory can be available for certain queries, even while other resource-intensive queries are running on another database of the Extended Parallel Server instance.

The basis of this new functionality is the construct of a resource class. This session variable determines what portion of shared memory is available for queries, and how many concurrent queries can access that memory. A DBSA can partition the total amount of shared memory for the server instance among resource classes by setting onconfig parameters. A session can be associated with a resource class in several ways:

• by default, if the session is associated with the built-in "DEFAULT" class
• by including the SET ENVIRONMENT DS_CLASS statement within the sysdbopen( ) procedure
• by executing SET ENVIRONMENT DS_CLASS before running a query
• by setting the DS_CLASS option of the IBM_XPS_PARAMS environment variable in the shell.

If DS_CLASS is an IMMUTABLE session attribute, however, the DBA can use sysdbopen( ) at connection time to restrict the resources of specific users.

With this feature, the DBSA can define up to eight resource classes and partition resources among these named classes. Every user session is associated with an explicit or default resource class. By reserving a specified proportion of total memory for the resources classes of sessions that execute critical operations, the DBSA can reduce the risk that insufficient resources will be available during critical DML operations.

This feature implements the following changes to legacy XPS 8.50 behavior:

• New configuration parameters to define attributes of up to eight resource classes. Each resource class section in the configuration file requires these four parameters:
  • DS_CLASS_NAME, specifying the name of the resource class
  • CLASS_DS_MEM_QUOTA, specifying the maximum percentage of available memory
  • CLASS_DS_MAX_QUERIES, specifying the maximum number of concurrent queries
  • END, marking the end of a resource class definition section in the configuration file.
• New syntax of the SET ENVIRONMENT statement to associate an existing resource class with the current user session, or to change the mutability of the DS_CLASS session environment variable:

  SET ENVIRONMENT DS_CLASS [ [ ds_class_name ] | [ IMMUTABLE | MUTABLE ] ] 

• New syntax of the onutil utility:

  onutil SET DS_CLASSINFO "ds_class_name:class_ds_mem_quota, class_ds_max_queries"

• New syntax for the onmode utility:

  onmode -q { IMMUTABLE | MUTABLE } DS_CLASS session_id

• New output from the onstat utility:

  onstat -g { env [ session_id ] | mut session_id | rgm | ses | cfg [DS_CLASSINFO] }

Here session-id is the identifier of a session, ds_class_name is a resource class, and class_ds_mem_quota and class_ds_max_queries are attributes of resource classes.

For more information about using resource classes, see Allocating Memory Through Resource Classes.