SSL_CTX_set_session_cache_mode, SSL_CTX_get_session_cache_mode – enable/disable session caching
http://www.openssl.org/docs/ssl/SSL_CTX_set_session_cache_mode.html

SSL_CTX_sess_set_cache_size, SSL_CTX_sess_get_cache_size – manipulate session cache size
http://www.openssl.org/docs/ssl/SSL_CTX_sess_set_cache_size.html