I executed the following command on our Oracle 9.2.0 RACed database on Compaq TRU64 Unix:

Reduced db_cache_size from 1008M to 608M:

alter system set db_cache_size = 629145600 scope=both sid='dbx2';

The db_cache_size did get reduced, but I did not see any memory freed to the o/s - does thit not happen instantaneously ??