Runstats on Partitioned Tablespaces - DB2/MVS 3.1
Geoffrey Daw
to 15 is historical and doesn't change much, if at all. Only partitions 16
and 17 are actively changed at this time. I wanted to make use of the new
feature in version 3.1 of running RUNSTATS only against specific partitions
to reduce my runstats time and costs. I ran my runstats last month against
all partitions. This month I ran it against partitions 16 and 17 of the
tablespace and index only. I include in my runstats only the columns that
are in indexes and to collect information for indexes. In this case I only
have the partitioning index and it contains 2 columns.
After I ran runstats against partitions 16 and 17 I checked the catalog to
see what was changed. I noticed that the COLCARD - number of distinct values
for the column - column in SYSIBM.SYSCOLUMNS had values for the first column
in the index but had 0 for the second column in the index. Previously the
value was over 11 million. I tried this out in a test environment and found
that when I ran runstats against all partitions the COLCARD value was
updated. When I run it against a couple partions only then it is set to 0.
The SYSIBM.SYSCOLSTATS information and other values were updated.
The Command and Utility Reference manual states that when you run runstats
against a single partition the partition level statistics that result are
used to update the aggregate statistics for the entire object. So I expected
the COLCARD value to be updated.
My question, after this long preamble, is this a normal occurrence for the
runstats utility and will it have any impact on the optimizer? If anyone
(IBM??) can enlighten me on this I would appreciate it.
Thanks in advance.
Geoffrey Daw, DBA, EDS Canada
Matt Watts
I saw this in the regular internet newsgroup comp.databases.ibm-db2
but
not in here. I don't have an answer for this guy, can anyone here
help
this fellow EDSer? Please reply directly to him.
Matt
--
The opinions expressed here are not necessarily those of
my employer. Nor are they necessarily my opinions, I
might have just found them laying around and decided to
use them here.