Analyze and explain the reasons for the difference between 5.4 and 5.5

Basic facts as known today:

• Available traces show 2x elapsed time between 5.4 and 5.5
• They also show 50% difference in LIO
• This is almost certainly NOT extent elimination problem. The reason for this statement is that when this query was run using utf8, it did not do extent elimination, and the difference was close to 4x on elapsed and 3x on LIO.
• Personal opinions point to CPU overhead of collations. But before this is positively determined - the difference in LIO needs to be explaind.
  REPEAT: this task is RESEARCH and diagnosis only. No solutions are to be proposed at this time.