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How do you stop phantom reads?
PHANTOM reads can be prevented by using SERIALIZABLE isolation level, the highest level. This level acquires RANGE locks thus preventing READ, Modification and INSERT operation on other transaction until the first transaction gets completed.
How the phantom problem can handled?
The so-called phantom problem occurs within a transaction when the same query produces different sets of rows at different times. For example, if a SELECT is executed twice, but returns a row the second time that was not returned the first time, the row is a “phantom” row.
What are phantom reads?
A Phantom read occurs when one user is repeating a read operation on the same records, but has new records in the results set: READ UNCOMMITTED. Also called a Dirty read. When this isolation level is used, a transaction can read uncommitted data that later may be rolled back.
How does Index locking resolve the phantom problem?
Index locking is a special case of predicate locking that is potentially more efficient for preventing the phantom problem. 1. If there is a dense index on the rating field then the transaction can lock index page containing the data with some predicate.
What are the three problems due to concurrency?
The concurrency control has the following three main problems: Lost updates. Dirty read (or uncommitted data). Unrepeatable read (or inconsistent retrievals).
What is a dirty read in SQL Server?
Dirty Reads A dirty read occurs when a transaction reads data that has not yet been committed. For example, suppose transaction 1 updates a row. Transaction 2 reads the updated row before transaction 1 commits the update. If transaction 1 reexecutes the statement that reads the rows, it gets a different set of rows.
How to deal with phantom read in SQL Server?
In order to do this, it places a range lock on the data return by the transaction which ensures that once a transaction reads the data, then no other transaction can read, update, delete or insert new data within that range. In the next article, I am going to discuss the Snapshot isolation level in SQL Server with an example.
How does SQL Server login to database work?
A SQL Server login created from a Windows user can enter a database if the Windows user is a member of a Windows group that is also a user in the database. Information about the mapping of a SQL Server login to a database user is stored within the database. It includes the name of the database user and the SID…
Where to find logon triggers in SQL Server?
Please use below SQL Script to create the Database, the Database Table and the Logon Trigger to audit the Logon Data. You can find the Trigger inside the Triggers folder which is inside the Server Object Folder as shown in the below image.
How to fix the phantom read concurrency problem?
In the above example, to fix the phantom read concurrency problem let set the transaction isolation level of Transaction 1 to serializable. The Serializable Transaction Isolation Level places a range lock on the rows returns by the transaction based on the condition.