SSL_session_cache_size

    If you make repeated connections to the same host/port and the SSL renegotiation time is an issue, you can turn on client-side session caching with this option by specifying a positive cache size. For successive connections, pass the SSL_reuse_ctx option to the new() calls (or use set_default_context()) to make use of the cached sessions. The session cache size refers to the number of unique host/port pairs that can be stored at one time; the oldest sessions in the cache will be removed if new ones are added.

SSL_session_cache

    Specifies session cache object which should be used instead of creating a new. Overrules SSL_session_cache_size. This option is useful if you want to reuse the cache, but not the rest of the context.
    A session cache object can be created using IO::Socket::SSL::Session_Cache->new( cachesize ).

    Use set_default_session_cache() to set a global cache object.