ubuntu fix mysqld high memory usage

###ubuntu fix mysqld high memory usage

vim /etc/mysql/mysql.conf.d/mysqld.cnf
key_buffer_size         = 6M
max_binlog_size   = 6M
max_allowed_packet      = 6M
table_open_cache       = 128
max_connections        = 15
table_definition_cache = 100
temptable_max_ram  = 16M
performance_schema=OFF
service mysql restart