title: nutch vs solr indexing
body: <p>I have recently started working on nutch and I am trying to understand how it works. As far as I know Nutch is basically used to crawl the web and solr/Lucene is used to index and search. But when I read documentation on nutch, it says that nutch also does inverted indexing. Does it uses Lucene internally to do indexing or does it have some other library for indexing? If it uses solr/lucene for indexing then why is it necessary to configure solr with nutch as the nutch tutorial says?</p>
  
  <p>Is the indexing done by default. I mean I run this command to start crawling. Is indexing happening here?</p>
  
  <pre><code>bin/nutch crawl urls -dir crawl -depth 3 -topN 5
  </code></pre>
  
  <p>Or does indexing happen only in this case. (According to tutorial:  If you have a Solr core already set up and wish to index to it, you are required to add the -solr  parameter to your crawl command e.g.)</p>
  
  <pre><code>bin/nutch crawl urls -solr http://localhost:8983/solr/ -depth 3 -topN 5
  </code></pre>