使用pt-online-schema-change不锁表修改表结构

1，pt-osc步骤

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修改表结构如添加索引、修改列，需要锁表，期间不能写入，使用pt-osc避免长时间锁表操作。在rename阶段是，也是会短暂锁表的

2，使用pt-osc添加唯一索引

1）扫描重复的client_id
select client_id, count(1) count from my_order_1.order_0 group by client_id having count>1;
2）将重复client_id修改
update my_order_1.order_0 b,(select client_id from my_order_1.order_0 where client_id = '1234567891234567') a set b.client_id = concat(b.client_id,b.id) where b.client_id = a.client_id;
3）使用pt-online-schema-change 修改表结构、增加唯一索引。
4）使用information_schema 构造sql
select concat('select client_id, count(1) count from ',table_schema,'.',table_name,' group by clinet_id having count>1;') from information_schema.tables where table_schema like '%order%' and table_name like '%_%'