db2pfchr processes and high CPU

[pike]

Hi
DB2 8.1 FP 7a on AIX 5.2.0.

Can anyone tell me how best to reduce high CPU (and subsequent high IO)
associated with db2pfchr processes?
NUMIO_SERVERS is set to the default 3. A grep on these prefetchers
returns:

2867326 1405102 3 Feb 24 - 1460:34 db2pfchr 0
3932384 1405102 0 Feb 24 - 42:48 db2pfchr 0
5415164 1405102 0 Feb 24 - 250:57 db2pfchr 0

As machine is memory-constrained, I'm reluctant to increase bufferpool
size.

Any tips / links much appreciated.
Thanks

[Ian]

pike wrote:

Hi
DB2 8.1 FP 7a on AIX 5.2.0.

Can anyone tell me how best to reduce high CPU (and subsequent high IO)
associated with db2pfchr processes?
NUMIO_SERVERS is set to the default 3. A grep on these prefetchers
returns:

2867326 1405102 3 Feb 24 - 1460:34 db2pfchr 0
3932384 1405102 0 Feb 24 - 42:48 db2pfchr 0
5415164 1405102 0 Feb 24 - 250:57 db2pfchr 0

As machine is memory-constrained, I'm reluctant to increase bufferpool
size.

The db2pfchr processes (pre-fetchers) are responsible for reading data
from disk and writing it to the bufferpool.

If you're finding that you have a lot of unread prefetch pages, that's
an indication of either having bufferpools that are too small or
prefetchsize too large for your tablespaces. If you can't increase
bufferpools...

Otherwise, there's not a lot you can do about their CPU utilization --
short of eliminating data from your database or preventing users from
running queries :-)