MAX_PDQPRIORITY

onconfig.std value

100

if not present

100

range of values

0 through 100

takes effect

On all user sessions

utilities

onmode -D
onstat -g mgm (See The onstat -g mgm Option.)

refer to

The following material:

• The chapter on using PDQ, in the IBM Informix Performance Guide
• Change Decision-Support Parameters

MAX_PDQPRIORITY limits the PDQ resources that the database server can allocate to any one DSS query. MAX_PDQPRIORITY is a factor that is used to scale the value of PDQ priority set by users. For example, suppose that the database administrator sets MAX_PDQPRIORITY to 80. If a user sets the PDQPRIORITY environment variable to 50 and then issues a query, the database server silently processes the query with a PDQ priority of 40.

You can use the onmode utility to change the value of MAX_PDQPRIORITY while the database server is online.

In Dynamic Server, PDQ resources include memory, CPU, disk I/O, and scan threads. MAX_PDQPRIORITY lets the database administrator run decision support concurrently with OLTP, without a deterioration of OLTP performance. However, if MAX_PDQPRIORITY is too low, the performance of decision- support queries can degrade.

You can set MAX_PDQPRIORITY to one of the following values.

Value

Database Server Action

0

Turns off PDQ. DSS queries use no parallelism.

1

Fetches data from fragmented tables in parallel (parallel scans) but uses no other form of parallelism.

100

Uses all available resources for processing queries in parallel.

number

An integer between 0 and 100. Sets the percentage of the user-requested PDQ resources actually allocated to the query.