MySQL: What does event `/io/table/sql/handler` mean? Yesterday I experienced a MySQL incident


the load was extremely high
All select statements takes more than 3 times time than usual.
All insert statements takes 10+ times time than usual.


The MySQL performance monitor tool shows: 


there are lots of /io/table/sql/handler has been generated during the period of incident.
lots of active threads within the period of incident.
lots of blocked thread within the period of incident.


Questions


What does /io/table/sql/handler mean?
Do you know the possible root cause?
From documentation of solorwinds


  .../sql/handler = work has been delegated to a storage engine
  
  examples:
  
  
  io/table/sql/handler = storage engine is processing an I/O request against a table
  lock/table/sql/handler = storage engine is processing a table lock operation
  


Reference


See the MySQL reference manual for more information on Wait Instrument naming (look at the section for "Wait Instrumented Components"):

https://dev.mysql.com/doc/refman/5.6/en/performance-schema-instrument-naming.html