The existence of those files has no impact on the performance of anything. It could impact lots of programs if you run out of disk space.
Such files are created temporarily during certain maintenance actions. When all goes well, those files will be deleted. You can remove them (if nothing like ALTER is busy running).
Since they are in
/tmp, the next reboot (of Linux) will remove them (and anything else in
You really should
- Upgrade from the antique version 5.1, AND
- Switch your tables to InnoDB.
If those came from a big "table" called "804" that is broken into lots of smaller tables, I must suggest that there are better ways to handle 'big' data. Most ways apply equally well to both MyISAM or InnoDB.
5.1 -> 5.5 -> 5.6 -> 5.7 -> 8.0 (MySQL)
MariaDB has an even longer chain of releases.