The number of current cache entries and the maximum number of cache entries are both displayed in perfdump. In the Admin console, they are called the Number of Entries and the Maximum Cache Size. A single cache entry represents a single URI.
The available address space for a 32-bit process like the Proxy server is limited to 4Gbytes. The max-entries for file cache is based on the number of threads (as specified by thread-pool/max-threads), and the connection queue size. It is recommended to cache small, frequently accessed cache files in the file cache and use perfdump to ensure that the file cache hit ratio is close to 100%. To achieve this, you may increase file cache size and fine tune the max-entries for optimal performance.