title: What is RDD dependency in Spark?
body: <p>As I know there are two types of dependencies: <strong>narrow &amp; wide</strong>. But I dont understand how dependency affects to <strong>child RDD</strong>. Is <strong>child RDD</strong> only metadata which contains info how to build new RDD blocks from <strong>parent RDD</strong>? Or <strong>child RDD</strong> is self-sufficient set of data which was created from <strong>parent RDD</strong>?</p>