David Jensen mentions in ☞ his notes on a Riak presentation:
If you’re a small team, unless you’re an Erlang shop, one downside to Riak is that it is primarily written in Erlang and C. Why is this a downside? I’ve heard a valid recommendation that when you are using these new NoSQL products, it really helps to know the language it was written in so that you can help track down the source of bugs (and maybe even submit patches). If you use the language it was written in on a daily basis, it makes that job much easier.
While many will probably dismiss immediately such a concern — basically the simplest counter-question would be: how many times have you had to debug your database? — I do feel that, psychologically at least, this is a valid concern.
Most of the NoSQL solutions are still quite young with 0 something version and that makes you ask how many 0.something solutions are you basing your project on?. For many of these NoSQL projects there are not so many experts around and that raises the questions: how quick can I get someone to help? how expensive will it be? will he/she be able to solve my problem?
So I’d say that every responsible software engineer will be a bit concerned about using a solution built on a language that is not known by anyone in the small dev team.
The real question is will this stop NoSQL adoption? . The answer is definitely NO, because we like shiny new toys and we like to hack things and even more importantly we start realizing that there are use cases where NoSQL solutions will make our lives much much easier.