mysql 5.6默认启动占用内存400多M，如果是vps等，明显偏高。
修改performance_schema_max_table_instances,table_definition_cache,table_open_cache这个三个参数，调低值能明显减小。
默认值如下：
performance_schema_max_table_instances 12500
table_definition_cache 1400
table_open_cache 2000
参数含义：
performance_schema_max_table_instances :The maximum number of instrumented table objects.
table_definition_cache:The number of table definitions (from .frm files) that can be stored in the definition cache
table_open_cache:The number of open tables for all threads.
调低如下：
performance_schema_max_table_instances = 200
table_definition_cache = 100
table_open_cache = 100
可降低到60多M左右。
进一步调整参数：
innodb_buffer_pool_size，innodb_additional_mem_pool_size，innodb_log_buffer_size这个三个参数可以调小。
再进一步调整： mysql 5.6默认启用performance_schema，占用很多内存，可以禁用。
完整配置文件如下，内存占用到22M：
cat /etc/my.cnf “`
[mysqld]
port = 3306
server_id = 1
socket = /tmp/mysql.sock
performance_schema = OFF
innodb_buffer_pool_size = 8M
innodb_additional_mem_pool_size = 1M
innodb_log_buffer_size = 1M
key_buffer_size = 0
query_cache_size = 0
log_bin = mysql-bin
basedir = /usr/local/mysql
datadir = /usr/local/mysql/data
sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES “`
