MAX_PDQPRIORITY configuration parameter

Use the MAX_PDQPRIORITY configuration parameter to limit the PDQ resources that the database server can allocate to any one DSS query.

onconfig.std value
MAX_PDQPRIORITY 100
values
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.

2 - 100 = Sets the percentage of the user-requested PDQ resources actually allocated to the query. 100 uses all available resources for processing queries in parallel.

takes effect
On all user sessions after you edit your onconfig file and restart the database server.
When you reset the value dynamically in your onconfig file by running the onmode -wf command.
When you reset the value in memory by running the onmode -wm command.

Usage

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 HCL Informix®, 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.


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