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What happens when another session tries to update the locked data?
What happens when another session tries to update the locked data? He will wait to get lock on the data till first user releases it. Once first user releases the lock, he immediately acquires lock on it and updates his data. Once second user’s transaction is complete, he releases the lock by committing his transaction.
What is two phase locking protocol?
According to the two-phase locking protocol, a transaction handles its locks in two distinct, consecutive phases during the transaction’s execution: Expanding phase (aka Growing phase): locks are acquired and no locks are released (the number of locks can only increase).
Does UPDATE lock table mysql?
A locking read, an UPDATE , or a DELETE generally set record locks on every index record that is scanned in the processing of an SQL statement. It does not matter whether there are WHERE conditions in the statement that would exclude the row.
What causes a lock on a SELECT query?
So if someone tries to insert into the table that the other SELECT is reading (in pages that SQL is trying to read), then a LOCK can occur and the two transactions block each other.
What happens when a lock is released in SQL Server?
Once the lock is released by committing the changes or by rolling back changes to initial state, other transactions will be allowed to make required data changes.
When to use lock timeout in SQL Server?
In SQL Server, when one session holds locks on a particular resource such as a table, row or key and a second session needs to obtain locks on the same resource, the second session may need to wait for the first session to release the needed locks before proceeding with the process.
You see that although the last transaction is completed, locks are held on both the authors and titleauthors tables. The reason is that the first transaction did not complete and when the second transaction was executed from the same connection, it was treated as a nested transaction.