乐趣区

关于数据库:乐观锁

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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