title: MySQL eating 80-100% CPU starting July 1 Midnight, a day or so following a EBS connectivity issue
body: <p>I am extremely curious about a recent issue that I experienced with all of my EC2 instances running MySQL.  On July 1st at 12:00 AM UTC, both of my Amazon EC2 instances (running in US-EAST region) fired an alarm indicating high CPU usage.  I investigated to find that it was MySQL that was eating all of the CPU.  I logged in and ran <code>SHOW PROCESSLIST</code> to find that <strong>no queries were running</strong> (these servers don't get hit much after business hours).  I stopped MySQL, CPU utilization dropped back down to 1-3% (as normal).  I restarted MySQL, and it started eating a lot of CPU again.  Then, I restarted the server <code>shutdown -r now</code>, and the problem went away.  Both servers had the exact same problem (running Ubuntu 12.04 LTS).</p>
  
  <p>The only relevant item I see in the syslog is:</p>
  
  <p><code>
  Jun 30 23:59:59 hostname kernel: [14152976.187987] Clock: inserting leap second 23:59:60 UTC
  </code></p>
  
  <p>I don't think that I have logging enabled for MySQL; whatever the default setting is for Ubuntu 12.04 is what I'm using.  If it makes any difference, most of the databases are InnoDB.</p>
  
  <p>A day prior, the one instance was affected by a EBS connectivity issue, which caused the server to respond extremely slowly when accessing the disk.  I don't believe the other instance was effected (it's in another AWS account and responded okay during the "outage"), but I can't be 100% sure.  I wonder if this might have caused MySQL to go crazy?  But why wait until midnight?  (Watch out! This might be the "red herring" in this mystery)</p>
  
  <p>Any thoughts on what might have caused this issue?</p>