title: Delete all keys from rocksdb (drop all)
body: <p>I have a rocksdb instance with multithreaded read/write access. At some point an arbitrary thread needs to process a request to clear the whole database, basically delete all keys. How can I do it with the smallest disturbance to the other threads? Obviously, as everything is  parallel, there is no need for a definite moment at which the database gets cleared and the new writes go to an empty one, and it is okay if some parallel reads are still getting the old data for some time.</p>
  <ul>
  <li>I see <code>DeleteRange</code>, but my keys are irregular, there is no such thing as an upper bound</li>
  <li>I see <code>DeleteFile</code>, but the comment says it will be gone in rocksdb 7.0. Also, this looks like a bad idea in a multithreaded environmnet</li>
  </ul>
  <p>Interestingly, I could not find a recipe for such seemingly common use case</p>