title: Huge number of range scans in geomesa cassandra
body: <p>I am trying to test geomesa cassandra backend.</p>
  
  <p>I have ingested a ~2M points from OSM and send <code>DWITHIN</code> and <code>BBOX</code> queries to cassandra using geomesa with geotools ecql.</p>
  
  <p>Then I've done some performance tests, the results do not look reasonable for me.</p>
  
  <p>Cassandra is installed to linux machine with 16 cores xeon, 32GB RAM and 1 SSD drive. I got <code>~150</code> queries per second.</p>
  
  <p>I started to investigate geomesa execution plan for my queries.</p>
  
  <p>Trace logs coming from <code>org.locationtech.geomesa.index.utils.Explainer</code> were really helpful, they do a great job explaining what is going on.</p>
  
  <p>What looks confusing to me is the number of range scans that go though cassandra.</p>
  
  <p>For example, I see the following in my logs:
  <code>
  Table: osm_poi_a7_c_osm_5fpoi_5fa7_attr_v2
  Ranges (49): SELECT * FROM ..
  </code></p>
  
  <p>The number <code>49</code> means the actual number of range scans sent to cassandra.
  Different queries give me different results, they vary approximately from ~10 to ~130.</p>
  
  <p><code>10</code> looks quite reasonable to me but <code>130</code> looks enormous.</p>
  
  <p>Could you please explain what causing geomesa to send so huge amount of range scans?</p>
  
  <p>Is there any way to decrease the number of range scans?</p>
  
  <p>Maybe there are some configuration options?</p>
  
  <p>Are there other options? like descreasing the presicion of z-index to improve such queries?</p>
  
  <p>Thanks anyway!</p>