在之前的版本，调整Innodb_Buffer_Pool_size大小必须重启mysql进程才可以生效，如今在MySQL5.7里，可以直接动态设置，方便了很多。
这个功能应用的场景：
一、机器增加内存，DBA粗心大意忘记调大Innodb_Buffer_Pool_size了
二、工作交接，新来的DBA发现前任DBA设置的Innodb_Buffer_Pool_size不合理
需要注意的地方，在调整Buffer_Pool期间，用户的请求将会阻塞，直到调整完毕，所以请勿在白天调整，在凌晨3-4点低峰期调整。
调整时，内部把数据页移动到一个新的位置，单位是块。如果想增加移动的速度，需要调整innodb_buffer_pool_chunk_size参数的大小，默认是128M。
例（把BP 128M增大为384M）：
mysql> SELECT @@innodb_buffer_pool_size; +---------------------------+ | @@innodb_buffer_pool_size | +---------------------------+ | 134217728 | +---------------------------+ 1 row in set (0.00 sec) mysql> SELECT @@innodb_buffer_pool_chunk_size; +---------------------------------+ | @@innodb_buffer_pool_chunk_size | +---------------------------------+ | 134217728 | +---------------------------------+ 1 row in set (0.00 sec) mysql> SET GLOBAL innodb_buffer_pool_size=402653184; Query OK, 0 rows affected (0.01 sec) mysql> SELECT @@innodb_buffer_pool_size; +---------------------------+ | @@innodb_buffer_pool_size | +---------------------------+ | 402653184 | +---------------------------+ 1 row in set (0.00 sec)
innodb_buffer_pool_chunk_size的大小，计算公式是innodb_buffer_pool_size / innodb_buffer_pool_instances
比如现在初始化innodb_buffer_pool_size为2G，innodb_buffer_pool_instances实例为4，innodb_buffer_pool_chunk_size设置为1G，那么会自动把innodb_buffer_pool_chunk_size 1G调整为512M，例：
./mysqld --innodb_buffer_pool_size=2147483648 --innodb_buffer_pool_instances=4
--innodb_buffer_pool_chunk_size=1073741824;
mysql> SELECT @@innodb_buffer_pool_size; +---------------------------+ | @@innodb_buffer_pool_size | +---------------------------+ | 2147483648 | +---------------------------+ 1 row in set (0.00 sec) mysql> SELECT @@innodb_buffer_pool_instances; +--------------------------------+ | @@innodb_buffer_pool_instances | +--------------------------------+ | 4 | +--------------------------------+ 1 row in set (0.00 sec) # Chunk size was set to 1GB (1073741824 bytes) on startup but was # truncated to innodb_buffer_pool_size / innodb_buffer_pool_instances mysql> SELECT @@innodb_buffer_pool_chunk_size; +---------------------------------+ | @@innodb_buffer_pool_chunk_size | +---------------------------------+ | 536870912 | +---------------------------------+ 1 row in set (0.00 sec)
监控Buffer Pool调整进程
mysql> SHOW STATUS WHERE Variable_name='InnoDB_buffer_pool_resize_status'; +----------------------------------+----------------------------------+ | Variable_name | Value | +----------------------------------+----------------------------------+ | Innodb_buffer_pool_resize_status | Resizing also other hash tables. | +----------------------------------+----------------------------------+ 1 row in set (0.00 sec)
查看错误日志：
（增大）
[Note] InnoDB: Resizing buffer pool from 134217728 to 4294967296. (unit=134217728) [Note] InnoDB: disabled adaptive hash index. [Note] InnoDB: buffer pool 0 : 31 chunks (253952 blocks) was added. [Note] InnoDB: buffer pool 0 : hash tables were resized. [Note] InnoDB: Resized hash tables at lock_sys, adaptive hash index, dictionary. [Note] InnoDB: completed to resize buffer pool from 134217728 to 4294967296. [Note] InnoDB: re-enabled adaptive hash index.
（减少）
[Note] InnoDB: Resizing buffer pool from 4294967296 to 134217728. (unit=134217728) [Note] InnoDB: disabled adaptive hash index. [Note] InnoDB: buffer pool 0 : start to withdraw the last 253952 blocks. [Note] InnoDB: buffer pool 0 : withdrew 253952 blocks from free list. tried to relocate 0 pages. (253952/253952) [Note] InnoDB: buffer pool 0 : withdrawn target 253952 blocks. [Note] InnoDB: buffer pool 0 : 31 chunks (253952 blocks) was freed. [Note] InnoDB: buffer pool 0 : hash tables were resized. [Note] InnoDB: Resized hash tables at lock_sys, adaptive hash index, dictionary. [Note] InnoDB: completed to resize buffer pool from 4294967296 to 134217728. [Note] InnoDB: re-enabled adaptive hash index.
