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乐观锁的惯例操作
select rev from table where id = $id
update table set name=$name, rev=rev+1 where id = $id and rev=$rev
此时有两个线程 a 和 b 来批改用户名
分成 4 中状况
1、
| a | b |
|---|
| select rev from table where id = $id | select rev from table where id = $id |
| update table set name=$name, rev=rev+1 where id = $id and rev=$rev rev=2 | |
| | update table set name=$name, rev=rev+1 where id = $id and rev=$rev 失败 |
| | |
| a | b |
|---|
| select rev from table where id = $id | select rev from table where id = $id |
| | update table set name=$name, rev=rev+1 where id = $id and rev=$rev rev=2 |
| update table set name=$name, rev=rev+1 where id = $id and rev=$rev 失败 | |
| | |
| a | b |
|---|
| select rev from table where id = $id | |
| update table set name=$name, rev=rev+1 where id = $id and rev=$rev rev=2 | |
| | select rev from table where id = $id |
| | update table set name=$name, rev=rev+1 where id = $id and rev=$rev rev=3 |
| a | b |
|---|
| | select rev from table where id = $id |
| | update table set name=$name, rev=rev+1 where id = $id and rev=$rev rev=2 |
| select rev from table where id = $id | |
| update table set name=$name, rev=rev+1 where id = $id and rev=$rev rev=3 | |
