Question

I have 2 SQL statements, that can be executed concurrently.
1st one updates request from Requests table, when request is taken for processing:

UPDATE Requests
SET IsInProcess = '1'

2nd one counts requests in process:

SELECT COUNT(*)
FROM Requests
WHERE IsInProcess = '1'

I need to count requests only after update statement is finished.
What transaction isolation levels or table hints do I need to use to accomplish this ?

Answer 1

You don’t have to use any. READ COMMITTED and default locking will do that. (Provided the update starts a bit earlier, otherwise the update will wait until you count.)

Given your where clause, it’s likely the server will take X lock on the whole table. Event if it doesn’t, the losing process will wait until the winning process releases its lock on the first updated/read row.