Runstats in DB2 V8 z/os

Jorg Lueke

Runstats in DB2 V8 z/os
We've now had several processes where the default setting in V8 resulted in
worse access paths. One recent application example shows the CPU going
from just under two hours to well over 10 hours,. In all cases when we run
the correct statistics the performance goes back to V7 levels or improves.
However, I am beginning to suspect that the default stats gathered during a
load are doing more harm than good at this point. Since the needed runstats
rly heavily on coldist for multiple columns, in some case non-indexed columns,
and the load update doesn't impact these we may need to run corrective
runstats after the loads. What I'm currently looking at is the CA load and
these workloads are Bi/warehousing large parallel queries.

There's also issues with the physical data design in that the notorious part_nbr
is being used to partition and cluster rather than the date field that is used in
almost all the queries.

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