Вы можете получить статистику по memcached, выполнив:
$ heroku run console
Running console attached to terminal... up, run.1
Loading production environment (Rails 3.1.3)
irb(main):001:0> Rails.cache.stats
Dalli/SASL authenticating as app590983%40heroku.com
Dalli/SASL: Authenticated
=> {"mc5.ec2.northscale.net:11211"=>{"evictions"=>"0", "curr_items"=>"627",
"total_items"=>"1257", "bytes"=>"2294318", "reclaimed"=>"0",
"engine_maxbytes"=>"5242880", "bucket_conns"=>"2", "pid"=>"319",
"uptime"=>"6710022", "time"=>"1330731177", "version"=>"1.4.4_207_g19c6b9e",
"libevent"=>"1.4.11-stable", "pointer_size"=>"64",
"rusage_user"=>"34354.590000", "rusage_system"=>"31381.520000",
"daemon_connections"=>"10", "curr_connections"=>"1211",
"total_connections"=>"14127919", "connection_structures"=>"1764",
"cmd_get"=>"9476", "cmd_set"=>"1257", "cmd_flush"=>"0", "auth_cmds"=>"24",
"auth_errors"=>"0", "get_hits"=>"8093", "get_misses"=>"1383",
"delete_misses"=>"0", "delete_hits"=>"0", "incr_misses"=>"0",
"incr_hits"=>"0", "decr_misses"=>"0", "decr_hits"=>"0", "cas_misses"=>"0",
"cas_hits"=>"0", "cas_badval"=>"0", "bytes_read"=>"21983909",
"bytes_written"=>"85267718", "limit_maxbytes"=>"67108864",
"rejected_conns"=>"0", "threads"=>"4", "conn_yields"=>"0"}}
PS: Я думаю, вам может понадобиться использовать драгоценный камень Далли, чтобы это сработало, но в любом случае это рекомендуемый клиент.
Вы также можете запустить Rails.cache.class
, чтобы увидеть, какой сервер использует Rails.