title: Performance when "findById" with "@PrimaryKeyClass"
body: <p>I want a <code>bulk-get</code> function with cassandra.</p>
  
  <p>But spring-data-cassandra's "findAllById" function  not working because <code>Cassandra supports single-field IN queries only</code>.</p>
  
  <p>So I try combining iteration with <code>findById</code> like this.</p>
  
  <pre><code>// Somekey : cassandra primary key object with @PrimaryKeyClass
  List&lt;Somekey&gt; keys = {add some keys};
  
  // SomeData : cassandra data
  List&lt;SomeData&gt; datas = new ArrayList&lt;&gt;();
  
  for (SomeKey : key : keys) {
    datas.add(someRepo.findById(key));
  }
  </code></pre>
  
  <p>But I think it is not good at performance for the following reasons.</p>
  
  <ol>
  <li>Cassandra sorts the data, but this is random access. (i think)</li>
  <li>Increasing network load in proportion to <code>keys.size()</code></li>
  </ol>
  
  <p>How do I use <code>bulk-get</code> function with cassandra??</p>
  
  <p>And, could I solve this performance problem with <code>ReactiveCassandraRepository</code>??</p>