Sun Java System Directory Server Enterprise Edition 6.1
Reference  Small, Medium, and Large Data Sets  A working set
refers to the data actually pulled into memory so the server can
respond to client applications. The data set here is then the
entries in the directory that you see are in fact getting used
due to client traffic. The data set may include every entry in
the directory, or may be composed most of the time of the some
smaller number of entries, such as entries corresponding to
people in a time zone where users are active.  We define three
data set sizes, based on how much of the directory data set fits
into available physical memory:   The data set fits entirely
into physical memory with fully-loaded database and entry
caches.   The data set fits in physical memory, and extra
physical memory can be dedicated to entry cache.   The data set
is too small to fit completely in available physical memory.
The ideal case is of course the small data set. If your data set
is small, set database cache size a