MySQL: What does event `/io/table/sql/handler` mean?

Question

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.

Questions

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

2. Do you know the possible root cause?

Answer 1

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

1. 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