A INSERT SQL is MySQL use memory too much

Question

when MySQL is running a insert data, the count of number is about 20w, and is about 100M but the memory useage is about more than 4G the SQL memory from

SELECT a.thread_id, a.event_name,
  sys.format_bytes(CURRENT_NUMBER_OF_BYTES_USED), sql_text
FROM performance_schema.memory_summary_by_thread_by_event_name a,
  performance_schema.events_statements_current b
WHERE a.thread_id=b.thread_id
ORDER BY CURRENT_NUMBER_OF_BYTES_USED DESC
LIMIT 10;

CURRENT_NUMBER_OF_BYTES_USED is about 3GB

why the insert SQL use so much memory