title: MemCache-using directed acyclic graph representing the dependencies of data?
body: <p>I am reading the paper of memached from facebook. One part it mentioned that it reduces the latency by fetching maximum number of items concurrently. Here is the quote:</p>
  
  <p>"We structure our web- application code to minimize the number of network round trips necessary to respond to page requests. We construct a directed acyclic graph (DAG) representing the dependencies between data. A web server uses this DAG to maximize the number of items that can be fetched concurrently. On average these batches consist of 24 keys per request."</p>
  
  <p>What data here it refers to? Web page? Pictures? How it can have dependencies to other data?</p>