my28_mysql内存占用过高降低的方法

对mysql做压力测试，测试完之后，mysql的内存一直不下降

$ free -m
              total        used        free      shared  buff/cache   available
Mem:
Swap:                                   

# top -u mysql

top - :: up  days, :,   users,  load average: 0.00, 0.85, 2.93
Tasks:  total,    running,  sleeping,    stopped,    zombie
%Cpu(s):  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem : +total,   free, +used,  buff/cache
KiB Swap:         total,         free,         used.  avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
  mysql          .154t .102t    S   0.0 82.9   : mysqld 

使用了0.102*1024=104G，需要0.154*1024=157G，buffer_pool占用了80G，一直不释放，调整buffer_pool_size到70G

mysql> show variables like '%pool_size%';
+-------------------------+-------------+
| Variable_name           | Value       |
+-------------------------+-------------+
| innodb_buffer_pool_size |  |
+-------------------------+-------------+
 row in set (0.00 sec)

mysql> select ***;
+-------------------+
| *** |
+-------------------+
|        |
+-------------------+
 row in set (0.00 sec)

mysql> set global innodb_buffer_pool_size=;
Query OK,  rows affected (0.01 sec)

调整后，内存立即就释放了；free和available两项都有增加

$ free -m
              total        used        free      shared  buff/cache   available
Mem:
Swap:                                   

之后又调整buffer_pool_size到80G，发现mysql占用的内存又慢慢上来了，看来mysql的buffer_pool_size会占用固定的内存大小。最后将buffer_pool_size设置为了物理内存的一半。