我是否需要事务/锁用于SQL Server中的此并发更新方案

Question

I am wondering whether I really do need transactions/locks in the following scenario. I can carry out 3 operations which might be concurrent in any number of them (ie I could have two Task 1 running and three Task 2 running):

Task 1:

select distinct count(some_id) as my_counter from table_1;
update table_2 set counter = my_counter;

Task 2:

insert into table_1 ...;
update table_2 set counter = counter + 1;

Task 3:

delete from table_1 where id = ...;
update table_2 set counter = counter - 1;

How should I implement the above being sure that I will never corrupt table_2's field counter ?

Thank you very much!

Answer 1

A few points:

• In any case you need to enclose the two statements of each task in a transaction.
• I think you need serializable transaction isolation level. Anything less will not do. For example using "repeatable read" task 1 might set table_2.counter to a stale value.
• You need to always access table_1 before table_2. This will ensure a consistent lock-ordering preventing deadlocks.

Answer 2

you can use TRIGGER for Task 2,3. it locks you tables in appropriate way. for Task 1 you should use XLOCK for row lock in your transaction