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Variable Recommended value
DB2_PARALLEL_IO Changes the way in which DB2 calculates I/O
parallelism to the tablespace. By default, DB2 sets I/O
parallelism to a tablespace equal to the number of
containers in that tablespace. For example, if the
tablespace has four containers, prefetches to that
tablespace are performed as four extent-sized prefetch
requests.
Set the DB2_PARALLEL_IO variable if you have
implemented containers on stripped devices (for
example, RAID-5, RAID-10, or RAID-01). If you set
DB2_PARALLEL_IO=ON or DB2_PARALLEL_IO=*,
DB2 assumes that containers are implemented on a
RAID 5 (6+1) configuration: six data disks plus one
parity disk.
In this example, prefetches to the four-container
tablespace mentioned above are performed in 24
extent-sized prefetch requests.
To assess the effectiveness of your prefetch parallel I/O
settings, monitor the unread_prefetch_pages and
prefetch_wait_time monitor element with the
snapshot_database monitor. The unread_prefetch_pages
monitor element tracks the number of prefetch pages
that were evicted from the buffer pool before it was
used. A continually growing number indicates that the
prefetch requests are too large, either because the
prefetch size is larger than the pages needed or the
prefetch activities are bringing in too many pages for
the capacity of the buffer pool. In either case, you may
want to consider reducing the prefetch size.
If you have high prefetch_wait_time values, the
application might be waiting for pages.
DB2_NUM_
CKPW_DAEMONS
0
Set this on IBM AIX 5.3 only if you observe a memory
leak during connect authentication within DB2's
authentication daemons (db2ckpwd processes) as a
result of calling the AIX loginsuccess() API.
Symptoms may include excessive memory usage, an
instance crash due to a trap in the db2ckpwd process,
or general authentication failures. Verify by monitoring
the SZ and RSS values for db2ckpwd processes. Use the
ps aux | grep db2ckpwd command and look at the fifth
and sixth columns of output.
DB2 workaround exists for this problem. Set the
following registry variable, and recycle this instance:
db2set DB2_NUM_CKPW_DAEMONS=0
Also see IBM APAR IY78341.
DB2LOCK_TO_RB STATEMENT
Performance Management 37