title: TensorBoard doesn't show all data points
body: <p>I was running a very long training (reinforcement learning with 20M steps) and writing summary every 10k steps. In between step 4M and 6M, I saw 2 peaks in my TensorBoard scalar chart for game score, then I let it run and went to sleep. In the morning, it was running at about step 12M, but the peaks between step 4M and 6M that I saw earlier disappeared from the chart. I tried to zoom in and found out that TensorBoard (randomly?) skipped some of the data points. I also tried to export the data but some data point including the peaks are also missing in the exported .csv.</p>
  
  <p>I looked for answers and found this in TensorFlow github page:</p>
  
  <blockquote>
    <p>TensorBoard uses reservoir sampling to downsample your data so that it can be loaded into RAM. You can modify the number of elements it will keep per tag in tensorboard/backend/server.py.</p>
  </blockquote>
  
  <p>Has anyone ever modified this server.py file? Where can I find the file and if I installed TensorFlow from source, do I have to recompile it after I modified the file? </p>