mysql 5.6、5.7默认启动占用内存400多M，如果是小内存vps，mysql内存占用率明显偏高,将会导致系统崩溃
编辑/etc/my.cnf文件在[mysqld]下增加或修改如下参数
performance_schema_max_table_instances = 200
table_definition_cache = 100
table_open_cache = 100。这个三个参数调低值后内存明显减小内存约60MB左右就大大降低默认使用的内存。
继续调整
innodb_buffer_pool_size=2M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
编辑vi /etc/my.cnf
# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.6/en/server-configuration-defaults.html
[mysqld]
#
# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M
#
# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin
#
# Remove leading # to set options mainly useful for reporting servers.
# The server defaults are faster for transactions and fast SELECTs.
# Adjust sizes as needed, experiment to find the optimal values.
# join_buffer_size = 128M
# sort_buffer_size = 2M
# read_rnd_buffer_size = 2M
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
#symbolic-links=0
skip-external-locking
key_buffer_size = 8M
max_allowed_packet = 1M
table_open_cache = 4
sort_buffer_size = 64K
read_buffer_size = 256K
read_rnd_buffer_size = 256K
net_buffer_length = 2K
thread_stack = 240K
#innodb_use_native_aio = 0
innodb_buffer_pool_size=2M
performance_schema_max_table_instances=50
table_definition_cache=50
table_open_cache=32
max_connections=50
max_user_connections=35
wait_timeout=10
interactive_timeout=15
long_query_time=5
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
# Recommended in standard MySQL setup
sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES
[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid