Performance system values: Parallel processing for queries and indexes

Specifies whether to use parallel processing and what to use it for. (QQRYDEGREE)

Parallel processing for queries and indexes, also known as QQRYDEGREE, is a member of the performance category of i5/OS™ system values. You can use this system value to specify whether to use parallel processing and what to use it for. To learn more, keep reading.

Quick reference
Location	In iSeries™ Navigator, select your system, > Configuration and Service > System Values > Performance > Database
Special authority	All object (ALLOBJ) and security administrator (SECADM)
Default value	Do not allow parallel processing
Changes take effect	Immediately
Lockable	No

What can I do with this system value?

Specifies whether to allow parallel processing and whether the type of parallel processing is input/output (I/O) parallel processing or symmetric multiprocessing (SMP). For I/O parallel processing, the database manager can use multiple tasks for input/output auxiliary storage processing for each query. Processing for the central processing unit (CPU) is still done serially. For symmetric multiprocessing, the CPU and I/O processing are assigned to tasks that run the query in parallel. Actual CPU parallelism requires a system with multiple processors. SMP parallelism is used only if the system feature DB2^® Symmetric Multiprocessing for i5/OS is installed.

Example: To determine what parts you need to buy for your company, you run a query of inventory from a database. By running the query, you determine which parts are sold out so you can replace them with new parts. The query takes a long time to complete because the processors cannot run at the same time. To increase the system performance, you should allow parallel processing. This allows different processors to run at the same time to perform the query much faster.

The following are possible options:

Do not allow parallel processing (*NONE)
No parallel processing is allowed for database query processing.
Use multiple processes for input/output (*IO)
The database query optimizer can use any number of tasks for I/O parallel processing for queries. SMP parallel processing is not allowed.
Use multiple processes for input/output, queries, and indexes (*OPTIMIZE)
The query optimizer can use any number of tasks for either I/O or SMP parallel processing for queries. If you select to use multiple processes for input/output, queries, and indexes, you can also select to Use all active memory in memory pool (*MAX). Using all active memory allows the query optimizer to choose an access plan that might consume more of the system resources, but would provide faster run time for a given query.

Where can I get more information about this system value?

To learn more, go to the performance system values overview topic. If you are looking for a specific system value or category of system values, try using the i5/OS system value finder.