If the directory data do not fit into available physical memory, or only just fit with no extra room to spare, set the entry cache sizes to the default value, 10M for entry-cache-size and allow the server to use as much of the operating system's file system cache as possible. Keeping some database cache available ensures that modifications remain cached between each database checkpoint.
If the directory data fit into available physical memory with physical memory to spare, allocate memory to the entry cache until either the entry cache is full or, on a 32–bit system, the entry cache reaches maximum size. Then allocate memory to the database cache until it is full or reaches maximum size.
See Configuring Memory in Oracle Fusion Middleware Administration Guide for Oracle Directory Server Enterprise Edition for instructions on setting cache sizes.