He meant to suggest mysqldumpslow, not mysqldump.
What values changed in SHOW VARIABLES?
Are you using MyISAM? Or InnoDB? Or both?
See
http://mysql.rjweb.org/doc.php/memory
This is excessive; 10 should be enough:
> thread_cache_size | 1024
> Current max_heap_table_size = 200 M
Be careful. Multiple copies of this could be created in RAM simultaneously, thereby leading to swapping. Swapping is I/O, and _really_ hurts MySQL performance.
> | Created_tmp_disk_tables | 601941 |
> | Created_tmp_tables | 980086 |
That is a big percentage, and a big number. We really need to see the digest of the slowlog to discuss this further. percona.com also has a nice tool for digesting the slowlog.