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 |
|
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