$ uname -a
Linux mysql 4.9.0-8-amd64 #1 SMP Debian 4.9.144-3.1 (2019-02-19) x86_64 GNU/Linux
$ mysql --version
mysql Ver 8.0.15 for Linux on x86_64 (MySQL Community Server - GPL)
在工作过程中，有很多过程在lsof中显示为“已删除”：
# lsof -u mysql | grep -F deleted | tail
mysqld 30953 mysql *752u REG 259,2 1048584 16813064 /tmp/mysql_temptable.sBa7Ou (deleted)
mysqld 30953 mysql *753u REG 259,2 1048584 16813066 /tmp/mysql_temptable.w49jlc (deleted)
mysqld 30953 mysql *754u REG 259,2 1048584 16813063 /tmp/mysql_temptable.xGEeE9 (deleted)
mysqld 30953 mysql *755u REG 259,2 1048584 16813067 /tmp/mysql_temptable.DJafvz (deleted)
mysqld 30953 mysql *756u REG 259,2 1048584 16813071 /tmp/mysql_temptable.VkIBPa (deleted)
mysqld 30953 mysql *761u REG 259,2 1048584 16813075 /tmp/mysql_temptable.1hwMuw (deleted)
mysqld 30953 mysql *762u REG 259,2 1048584 16813068 /tmp/mysql_temptable.Ogtc0W (deleted)
mysqld 30953 mysql *763u REG 259,2 1048584 16813069 /tmp/mysql_temptable.Tq7Gxk (deleted)
mysqld 30953 mysql *769u REG 259,2 1048584 16813072 /tmp/mysql_temptable.4wjILK (deleted)
mysqld 30953 mysql *770u REG 259,2 1048584 16813073 /tmp/mysql_temptable.rcrwKk (deleted)
有很多这样的过程，随着时间的推移，它们会占用整个内存：
# lsof -u mysql | grep -cF deleted
33532
仅重新启动mysql有帮助。 为什么会出现这些过程以及如何消除它们？