If /tmp directory get exhaust intemittent and, could find that the temporary files created are from MySQL, you could change the MySQL tmp directory.
Open,
#vi /etc/my.cnf
#tmpdir=/home/mysqltmp
#chmod 1777 /home/mysqltmp
Verify that the tmp directory is created using the following command.
#mysqladmin var | grep tmpdir
Open,
#vi /etc/my.cnf
#tmpdir=/home/mysqltmp
#chmod 1777 /home/mysqltmp
Verify that the tmp directory is created using the following command.
#mysqladmin var | grep tmpdir