Why sometimes mysqld loads percent along with the disk?

Question

MySQL

Are there any tools to understand why this is happening?
It seems that at this time no complex queries are being executed.
1GB per second is strong, of course, I have at least 20 thousand records in the database and 10-20% of the processor is constantly loaded on average, but sometimes there are such jumps.

Answer 1

mysql> SHOW FULL PROCESSLIST

Answer 2

optimization and indexing most likely.