In fact I was watching a presentation somewhere (I forget where), where folks were using NoSQL databases as a sort of pre-processing layer for the RDBMS. In th

In fact I was watching a presentation somewhere (I forget where), where folks were using NoSQL databases as a sort of pre-processing layer for the RDBMS. In this regard it's very useful on the high-end. Where I am less convinced is outside the high-end, and outside the idea of a transition tier between input and RDBMS (or between RDBMS and output even). As a persistence layer, NoSQL is applicable largely to the subset of cases where Object Oriented Databases were. Here the GP is right that the industry is keen on relearning the same lessons every couple of decades.... However, as pre-processing and post-processing, there seems to me to be a much larger set of use cases out there but again only where the RDBMS is no longer really able to handle everything you want it to do.