Since the accepted answer is only connecting to remote hosts, it is obvious thatit will be always slower than localhost. Even if it is the next computer in your home, it would take milliseconds to read from that computer, but local memory takes only nanoseconds. You should compare them by using locally installed servers.

Here are my results from my local pc: You see, redis is almost as fast as in-memory in under high load. You can clone my the repo that these test codes are available: 

node.js session store 有可选的四种方法的性能测试如下：

Concurrency: 1none       4484.86 [#/sec] memory     2144.15 [#/sec] redis      1891.96 [#/sec] mongo      710.85 [#/sec] Concurrency: 10none       5737.21 [#/sec] memory     3336.45 [#/sec] redis      3164.84 [#/sec] mongo      1783.65 [#/sec] Concurrency: 100none       5500.41 [#/sec] memory     3274.33 [#/sec] redis      3269.49 [#/sec] mongo      2416.72 [#/sec] Concurrency: 500none       5008.14 [#/sec] memory     3137.93 [#/sec] redis      3122.37 [#/sec] mongo      2258.21 [#/sec]

对比得出redis来存储在并发性越多的情况下性能优越。

    The session used pages are very simple pages;

app.get("/", function(req,res){    if ( req.session && req.session.user_id){        req.session.no = req.session.user_id;    } else {        throw Error('error');    }    res.send("No: " + req.session.no);});

Redis store config:

app.use(express.session({    store: new RedisStore({        host: 'localhost',        port: 6379,        db: 2,        }),    secret: 'hello'}));

Mongo store config:

app.use(express.cookieParser());app.use(express.session({    store: new MongoStore({        url: 'mongodb://localhost/test-session'    }),    secret: 'hello'}));

 在使用mongodb存储时别忘记在加载一个模块：connect-mongo

npm install connect-mongo