You can use the QQRYDEGREE system value to control parallel processing for
a system. The current value of the system value can be displayed or
modified using the following CL commands:
- WRKSYSVAL - Work with System Value
- CHGSYSVAL - Change System Value
- DSPSYSVAL - Display System Value
- RTVSYSVAL - Retrieve System Value
The special values for QQRYDEGREE control whether parallel processing is
allowed by default for all jobs on the system. The possible values
are:
- *NONE
- No parallel processing is allowed for database query processing.
- *IO
- I/O parallel processing is allowed for queries.
- *OPTIMIZE
- The query optimizer can choose to use any number of tasks for either I/O
or SMP parallel processing to process the queries. SMP parallel
processing is used only if the DB2 UDB Symmetric Multiprocessing feature is
installed. The query optimizer chooses to use parallel processing to
minimize elapsed time based on the job's share of the memory in the
pool.
- *MAX
- The query optimizer can choose to use either I/O or SMP parallel
processing to process the query. SMP parallel processing can be used
only if the DB2 UDB Symmetric Multiprocessing feature is installed. The
choices made by the query optimizer are similar to those made for parameter
value *OPTIMIZE, except the optimizer assumes that all active memory in the
pool can be used to process the query.
The default value of the QQRYDEGREE system value is *NONE, so the value
must be changed if parallel query processing is desired as the default for
jobs run on the system.
Changing this system value affects all jobs that will be run or are
currently running on the system whose DEGREE query attribute is
*SYSVAL. However, queries that have already been started or queries
using reusable ODPs are not affected.
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