Ruby:创建一个更快的字符串缓存:数组还是SQL?

I'm making a ruby server with a cache of info about the online clients. This info should be preserved when I turn off the server. I can store it in a simple array and save it with Marshal or I can use a SQL database (MySQL, probably). Which is better to use? I think the Array method is easly, but the SQL is faster than? Thanks!I'm making a ruby server with a cache of info a