1) db2support -d -c –cl 1 –sf
Optimizer data gathered only for the tables involved in the query.
2) db2support -d -c –cl 0
Optimizer data collected for all objects in the database. Make sure to get the access plan via db2exfmt as well for support if using –cl 0 as we don’t get the plan with this method. Useful when there are few queries having issues.
3) If you have a good vs bad comparison, makes it easier for support/development to analyse.
4) Gather supporting information, such as iterative snapshots for ALL, cardinality estimates if possible, anything else which may make the debugging faster.
5) in v97, To collect optimizer related information for different optimization levels, including db2batch information for all optimization levels, issue:
db2support -d -c -cl 3 -sf -ol 0,1,2,3,5,7 -extenddb2batch

The -basic option limits the data gathered by the db2support tool to the optimizer-related diagnostic information.
The -ol option has been enhanced to support gathering data for multiple optimization levels.
The -extenddb2batch option allows db2batch information to be collected for all optimization levels when used with the -ol and -cl options.
The -nl | -nodb2look and -nc | -nocatalog options prevent the collection of db2look information and catalog information respectively.