MySQL is the database of choice for most OpenStack components
  (Ceilometer is a notable exception). If you start with a small
  deployment, it will probably run like a charm. But as soon as the
  dataset grows, you will suddenly face several challenges. We will
  write a series of blog posts explaining the issues you may hit
  and how to overcome them.
  Where is MySQL used in OpenStack?
  Have a look at the logical diagram of OpenStack below
  (click the image for a larger view).
   
  
  The diagram is a bit outdated: Neutron appears as Quantum and
  newer components like Heat are not pictured. But it shows that a
  database has to be used to store metadata or runtime information.
  And although …
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