if you running DB2 on AIX, make sure your VMO kernel setting OK

It is not uncommon that database system having performance problem due to less optimized VMO setting.

In AIX 6, its default setting is good (typically no need to change)

In AIX 5L, its default setting is no good. Many production systems use the default.

Make sure you understand them and ask your SA to check it out:

specifically the values of maxperm and minperm and few others