#2: REORG the DB2 Catalog
As of DB2 V4 the DB2 Catalog can be reorganized using the REORG utility; there are special rules for groupings of catalog tables and regarding sequence and coupling of system catalog and directory table spaces:
Don’t waste a lot of time here!
Though useful, you got along for a decade without reorganizing the DB2 system catalog, so don’t do it more than once a year (usually)