title: Semantics of ib_buffer_pool file in MySQL
body: <p>MySQL's default storage engine, InnoDB, maintains an internal buffer pool of database pages. In newer versions of MySQL (e.g. 5.7+) the space and page IDs of the pages in the buffer pool are persisted to disk in the "ib_buffer_pool" file. </p>
  
  <p>I'm curious about how this file is constructed, and <strong>in particular if the relative young-ness/old-ness of the pages in the buffer pool persists across restarts.</strong> In other words, if some page in the pool is younger than some other page, will that relationship hold after the file is written to, and then read from, the disk?</p>
  
  <p>A broader question is the following: <strong>how much of the state of the InnoDB buffer pool persists across restarts?</strong></p>