title: What types of situations are suited to use both a relational and NoSQL database?
body: <p>This is not a NoSQL vs. SQL type question. I am interested in types of scenarios where one can use a combination of a RDBMS and NoSQL database and the <strong><em>use of the combination is well suited</em></strong>. In general, I understand the "it depends" on the situation and task at hand, but my thinking is that there must be some general/common<sup>1</sup> situations where this combination is very useful. </p>
  
  <p><strong>Each of the above types of solutions have there own strengths and weaknesses - what I am after is situations/scenarios where the strengths of both can be fully exploited and utilised.</strong> </p>
  
  <p>In my mind, one could be E-commerce. Payments, transactions etc on a RDBMS (think ACID<sup>2</sup>) and product information and catalogues in a NoSQL database. But, is it suitable? </p>
  
  <p>Cross cutting concerns of an application eg. Logging is probably well suited for a NoSQL type solution as another example.</p>
  
  <p>Alternatively, why would you not use both these types of technologies in combination? </p>
  
  <p>Edit: Just to reiterate, I understand that that both SQL and NoSQL have their inherent advantages and disadvantages and that that certain types of situations are more suited to only one of the above data stores. </p>
  
  <p><sup>1</sup> Iknow the giants like Facebook, Google etc probably use a combination of these, but in <strike>almost all</strike> most cases I don't think most SO members will ever work on such huge solutions. More typical day-to-day type stuff. </p>
  
  <p><sup>2</sup> RavenDB is a NoSQL solution that supports ACID transactions</p>