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Why locks are used in transaction?
Transactions use locks to control concurrent access to data, achieving two important database goals: Consistency ensures that the data you are viewing or changing is not changed by other users until you are finished with the data.
Does transaction lock the row?
A transaction holds exclusive row locks for all rows inserted, updated, or deleted within the transaction. For example, assume that a transaction uses a SELECT statement with the FOR UPDATE clause to lock rows of a table. As a result, it acquires the exclusive row locks and a row share table lock for the table.
What is lock in transaction?
Lock Based Protocols in DBMS is a mechanism in which a transaction cannot Read or Write the data until it acquires an appropriate lock. A lock is a data variable which is associated with a data item. This lock signifies that operations that can be performed on the data item.
Which is not a state of a transaction?
10. Which of the following is not a transaction state? Explanation: Compensated is not a transaction state. But active, partially committed and failed are different states of a transaction.
Does MySQL transaction lock row?
1 Answer. A single statement like that works the same with MyISAM or InnoDB, with a transaction or with autocommit=ON. InnoDB locks only rows, not tables.
How does acquiring the intent lock affect the row lock?
By acquiring the intent lock, the transaction will not allow other transactions to acquire the exclusive lock on that table (otherwise, exclusive lock imposed by some other transaction would cancel the row lock).
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.
What are transaction locking and row versioning mechanisms?
This guide describes the locking and row versioning mechanisms the SQL Server Database Engine uses to ensure the physical integrity of each transaction and provides information on how applications can control transactions efficiently. Applies to: SQL Server 2005 (9.x) through SQL Server 2017, unless noted otherwise.
What happens when an error occurs during a transaction?
If an error occurs during the transaction, you roll back to cancel it. Any statements executed up to that point within the transaction are undone, leaving the database in the state it was in prior to the point at which the transaction began.