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:

  1. there are lots of /io/table/sql/handler has been generated during the period of incident.

  2. lots of active threads within the period of incident.

  3. lots of blocked thread within the period of incident.


  1. What does /io/table/sql/handler mean?

  2. Do you know the possible root cause?

enter image description here

  • 1
    Starting about 3am, there was at least one nasty query running. Or perhaps lots. Find them and let's discuss them. Maybe an ALTER, maybe a dump, maybe some complex SELECT. The slowlog, if on, would have caught it.
    – Rick James
    Commented Oct 25, 2018 at 19:46

1 Answer 1


From documentation of solorwinds

.../sql/handler = work has been delegated to a storage engine


  • 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


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


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.