[patio11]

It depends on what your simple application does and what its needs are. I could rewrite either of my products to use Redis only, to the exclusion of SQL. It wouldn't be a very good use of my time, but it would be trivially possible. Neither of them put terrible stress on persistence engines. Heck, I could rewrite them to do everything in flat files and that wouldn't be impossible, either.

There are some rather relational-data-intensive projects I've been involved with where that would have been an Exceptionally Poor Idea, both for the amount of pain one would go through writing a poorly tested version of LEFT JOIN to be able to get it to work, and because one will eventually discover that your SQL database of choice has been improved for hundreds of man-years along axes you care about and Redis has not.

[clojurerocks]

I guess what im wondering is more about the scalability of it. I know that Mongodb could essentially be used as the only datastore however it apparently has some issues currently with scalability.

[apgwoz]

So, your app is unlikely to be as popular as foursquare, for instance, at least right now, and they seem fine and happy with MongoDB. You might recall the issues they had with it a while back, but those have all been fixed as far as I'm aware. 10gen is really quite impressive when it comes to support, etc.

But, the real question is, why do you think a SQL database will not be scalable to begin with? I'm going to say that well over 75% of the top sites, use a SQL database.

[mrgordon]

Mongo 1.8 fixed a lot of the scalability issues. +1 to Mongo as an alternative to SQL. Redis is great for a simple app but I wouldn't want to scale it to handle everything for a large site.

[clojurerocks]

I didnt know that the issues in Mongo were fixed. I figured they would be eventually though.