Question

well,the topic introduce Isolation in wikipedia have such words,links is here

………
Serializable
This is the highest isolation level.
With a lock-based concurrency control DBMS implementation, serializability requires read and write locks (acquired on selected data) to be released at the end of the transaction. Also range-locks must be acquired when a SELECT query uses a ranged WHERE clause, especially to avoid the phantom reads phenomenon (see below).
When using non-lock based concurrency control, no locks are acquired; however, if the system detects a write collision among several concurrent transactions, only one of them is allowed to commit. See snapshot isolation for more details on this topic.

but whole topic didn’t explain “range-locks”,google alse have no accurate description.

what’s “range-locks”,and which different with “read lock” and “write lock”?

thanks!

Answer 1

If you use a range in the WHERE clause the database will lock each possible tuple in this range and also the next tuple (before and after). If there is no next tuple available in a direction it will lock completely in this direction.

So the SELECT is reliable within the transaction.