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.