DBA control of resources allocated to decision-support queries

A DBA can control the resources that the database server allocates to decision-support queries by setting the DS_TOTAL_MEMORY, DS_MAX_SCANS, and DS_MAX_QUERIES configuration parameters.

In addition to setting limits for decision-support memory and the number of decision-support queries that can run concurrently, the database server uses these parameters to determine the amount of memory to allocate to individual decision-support queries as users submit them. To do so, the database server first calculates a unit of memory called a quantum by dividing DS_TOTAL_MEMORY by DS_MAX_QUERIES. When a user issues a query, the database server allocates a percent of the available quanta equal to the PDQ priority of the query.

You can also limit the number of concurrent decision-support scans that the database server allows by setting the DS_MAX_SCANS configuration parameter.

Previous versions of the database server allowed you to set a PDQ priority configuration parameter in the ONCONFIG file. If your applications depend on a global setting for PDQ priority, you can use one of the following methods:
  • For UNIX: Define PDQPRIORITY as a shared environment variable in the informix.rc file. For more information about the informix.rc file, see the IBM® Informix® Guide to SQL: Reference.
  • For Windows: Set the PDQPRIORITY environment variable for a particular group through a logon profile. For more information about the logon profile, see your operating-system manual.

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