title: Cassandra and aggregated data
body: <p>We have a "legacy" SQL Server-based application which keeps OLTP data (sales):</p>
  
  <ul>
  <li>OLTP data structure is very complex</li>
  <li>Still we must keep it as a source for reports</li>
  <li>Reports over OLTP structures are very slow</li>
  <li>So we prepare and keep actual "OLAP"-views, say, sales per day, each view is actually a table in MS SQL database</li>
  </ul>
  
  <p>Main problem: when we need a new view it takes a lot of time to scan all existing OLTP data.</p>
  
  <p>Now we want to migrate to Cassandra, should we use same approach to achive same goals or:</p>
  
  <ul>
  <li>May be we better use tools like Spark/Kylin, can they do things like this?</li>
  <li>May be approach can be changed somehow?</li>
  </ul>