1) MDC (Multi-Dimension Clustering) with the appropriate fixpack (not sure whether its 8 or 10) can probably help you with 1.
In MDC, if your query has an exact match for one of the dimensions, then the deletes will (may) not log the actual rows/records being deleted, but just the data/index page information.
Look up the online DB2 documentation for details -
http://publib.boulder.ibm.com/infoce...n/r0009949.htm
Note that you will need the right fixpack AND the DB2_MDC_ROLLOUT registry variable set to ON (note that this is a ONE-WAY street - it can't be undone).
You can get more info on the DB2 profile registry variable at
http://publib.boulder.ibm.com/infoce...n/r0009949.htm
2) For this I think the only way out would be to NOT enforce your constraint.