title: simple mongo query to aggregate collections stats
body: <p>I'm trying to figure out if there's a nice way to get a result set from mongo that would give me an over view of all collections in a db.</p>
  
  <p>I see the stats method per collection, which includes a storageSize field that I'm interested in.   I'd like to get collections and their storageSizes in a single query with out just doing</p>
  
  <pre><code>db.col1.stats();
  db.col2.stats();
  db.col3.stats();
  </code></pre>
  
  <p>In MySQL the equivalant query of what I'm trying to do could look like</p>
  
  <pre><code>select table_schema, table_name, sum(data_length+index_length) from       
  information_schema.tables group by 1,2;
  </code></pre>