The Performance Schema and sys schema are great for
  investigating what is going on in MySQL including investigating
  performance issues. In my work in MySQL Support, I have a several
  times heard questions whether a peak in the InnoDB Data File
  I/O – Latency graph in MySQL Enterprise Monitor (MEM) or
  some values from the corresponding tables and view in the
  Performance Schema and sys schema are cause for
  concern. This blog will discuss what these observations means and
  how to use them.
  
The Tables and Views Involved
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