title: Efficiently scanning on composite row key in hbase
body: <p>I have my hbase table structured as follows:</p>
  
  <pre><code>a1:b1
  a1:b2
  a2:b1
  a3:b2
  </code></pre>
  
  <p>Is there any way I can efficiently check if the first part of the row key exists in the hbase table? I do not want to retrieve the records,
  I just want to check if a1, a2, a3 exist.</p>