title: Read value in rocksdb in chunks
body: <p>I want to read a really huge value stored in rocksdb. Is it possible to read it part by part?
  Like reading a file's content into a fixed buffer...</p>
  
  <p>for example I have a 500 MB value, that is a zlib-compressed file. as this is a server program, I can't allocate 500 MB to every connection ( 500 MB for value, that may be more anyway, and SSL context, authentication info, etc...).</p>
  
  <p>And also, this values have a meaning to protocol so I can't part it up.
  According to documentation, value size must be smaller than 3GB. I don't think any server program allocate this size for a single connection.</p>
  
  <p>I can mention some examples that can be usefull:</p>
  
  <ol>
  <li>making a filesystem on top of RocksDB</li>
  <li>Storing sounds, images, videos,... in a messaging app</li>
  </ol>
  
  <p>Suppose such an example:</p>
  
  <pre class="lang-cpp prettyprint-override"><code>Slice partialSlice;
  db-&gt;Get(opt,"ac154df568bb874", &amp;partialSlice, 256*1024);  /// read 256KB at once
  socket.write(partialSlice.data(), 256*1024);
  while(partialSlice.HaveRemaining) {
     /// repate it to get all of data...
  }
  </code></pre>