The entry cache holds recently accessed entries that are formatted for delivery to client applications. The entry cache is allocated as required until it reaches the a size larger than, but based on the maximum entry cache size you specify.
As entries stored in the entry cache are already formatted, Directory Server returns entries from an entry cache efficiently. Entries in the database must be formatted and stored in the entry cache before they are delivered to client applications.
The maximum size you specify indicates how much memory Directory Server requests from the underlying memory allocation library. Depending on how the memory allocation library handles requests for memory, the actual memory used may be much larger than the amount of memory available to Directory Server for the entry cache.
The memory used by the Directory Server process depends on the memory allocation library that is used, and depends on the entries cached. Entries with many small attribute values usually require more overhead than entries with few large attribute values.
For 32-bit servers, the entry cache size must be limited so that the total Directory Server ns-slapd process size is less than the maximum process size allowed by the operating system. In practice, this limit is generally in the 2-3 GB range.