title: When two pages is next to each other, how many times of random IO will happen?
body: <p>In 6.830 lec6, it said after converted a unclustered index into a clustered index for a range query, the times of random I/O will be decreased from per record to per page. So here implies that if two pages is next to each other, there will be 2 random I/O to be done.</p>
  <p>But it still says one of the characteristics of heap file is <code>Sequentially stored pages, no seeks between records or pages</code> , so here implies only 1 random I/O will happen.</p>
  <p><a href="https://i.stack.imgur.com/r4eQo.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/r4eQo.png" alt="Range query using unclustered Index, with per record random I/O" /></a></p>
  <p><a href="https://i.stack.imgur.com/dxOyZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dxOyZ.png" alt="Range query using clustered Index, with per record random I/O" /></a></p>
  <p><a href="https://i.stack.imgur.com/sxyZl.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sxyZl.png" alt="Heap File feature" /></a></p>