1，操作原因：
线上表访问比较慢，update尤其慢，查了下，max(id)有146亿了，但是总记录数才2亿，所以怀疑是以前做了太多delete操作导致碎片过多引起的，所以决定做optimize操作。
2，环境
MySQL cdb实例，版本5.6.34，共享实例非物理独占类型。
3，操作前措施：
为了安全起见，停止应用写操作，应用读操作保留
4，操作方案选择：
刚准备用alter table xxxxx ，虽然5.6 在线ddl不锁全表了，但是考虑到万一故障了，回滚起来就慢的要死，说不定有可能坏表，就暂时放弃了。
最终选择pt-online-schema-change工具进行操作。
5，操作时间
半夜1点，应用发布后立即执行操作。
6，操作过程：
[huangshan@db1ys] ~/pt$ bash -x muzhi_2.sh
+ pt-online-schema-change --recursion-method=none --no-version-check --execute --alter 'engine=innodb;' h=172.20.200.251,P=3306,u=root,p=L0xxFy3e4xhmsaml,D=user_db,t=huayuan_devices
No slaves found. See --recursion-method if host TENCENT64.site has slaves.
Not checking slave lag because no slaves were found and --check-slave-lag was not specified.
Operation, tries, wait:
analyze_table, 10, 1
copy_rows, 10, 0.25
create_triggers, 10, 1
drop_triggers, 10, 1
swap_tables, 10, 1
update_foreign_keys, 10, 1
Altering `user_db`.`huayuan_devices`...
Creating new table...
Created new table user_db._huayuan_devices_new OK.
Altering new table...
Altered `user_db`.`_huayuan_devices_new` OK.
2017-08-30T01:20:26 Creating triggers...
2017-08-30T01:20:26 Created triggers OK.
2017-08-30T01:20:26 Copying approximately 284468721 rows...
Copying `user_db`.`huayuan_devices`: 0% 02:04:22 remain
Copying `user_db`.`huayuan_devices`: 0% 02:10:22 remain
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2017-08-30T03:54:44 Copied rows OK.
2017-08-30T03:54:44 Analyzing new table...
2017-08-30T03:54:44 Swapping tables...
2017-08-30T03:54:44 Swapped original and new tables OK.
2017-08-30T03:54:44 Dropping old table...
2017-08-30T03:55:20 Dropped old table `user_db`.`_huayuan_devices_old` OK.
2017-08-30T03:55:20 Dropping triggers...
2017-08-30T03:55:20 Dropped triggers OK.
Successfully altered `user_db`.`huayuan_devices`.
[huangshan@db1ys] ~/pt$