title: N1QL Error Index scan timed out - cause: Index scan timed out
body: <p>I'm facing an issue on couchbase 4.1.0 running a query through CBQ against about 20 Million documents. When executing my query this error is printed after a 2 minute timeout:</p>
  <blockquote>
  <p>&quot;code&quot;: 12015,</p>
  <p>&quot;msg&quot;: &quot;Index scan timed out - cause: Index scan timed out&quot;.</p>
  </blockquote>
  <p>My questions are this</p>
  <ol>
  <li>What is an index scan (is this a scan looking for the appropriate index to use or something?</li>
  <li>What causes such an error</li>
  <li>Is querying a dataset of this size beyond the capabilities of couchbase?</li>
  </ol>