To manage the total amount of resources that the database server allocates to parallel database queries, the database server administrator sets the environment variable and configuration parameters that the following sections discuss.
To control resources allocated to PDQ, you can set the PDQPRIORITY environment variable. The queries that do not set the PDQPRIORITY environment variable before they issue a query do not use PDQ. In addition, to place a ceiling on user-specified PDQ priority levels, you can set the MAX_PDQPRIORITY configuration parameter.
When you set the PDQPRIORITY environment variable and MAX_PDQPRIORITY parameter, you exert control over the resources that the database server allocates between OLTP and DSS applications. For example, if OLTP processing is particularly heavy during a certain period of the day, you might want to set MAX_PDQPRIORITY to 0. This configuration parameter puts a ceiling on the resources requested by users who use the PDQPRIORITY environment variable, so PDQ is turned off until you reset MAX_PDQPRIORITY to a nonzero value.
To control the resources that the database server allocates to decision-support queries, set 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: