Home » Microsoft » MB6-886 » What type of isolation should be used for the query to return results fast?
You have a stored procedure that uses a SELECT statement to retrieve a sample data set from a table. It has been determined that the query is taking too long to return data.
Given that some inconsistent data can be allowed to appear. What type of isolation should be used for the query to return results fast?
A. Repeatable Read
B. Read Uncommited
C. ReadCommitted
D. ReadCommitted Snapshot
Correct Answer: B
Explanation/Reference:
READ UNCOMMITTED
Specifies that statements can read rows that have been modified by other transactions but not yet committed.
Transactions running at the READ UNCOMMITTED level do not issue shared locks to prevent other transactions from modifying data read by the current transaction. READ UNCOMMITTED transactions are also not blocked by exclusive locks that would prevent the current transaction from reading rows that have been modified but not committed by other transactions. When this option is set, it is possible to read uncommitted modifications, which are called dirty reads.
Values in the data can be changed and rows can appear or disappear in the data set before the end of the transaction. This option has the same effect as setting NOLOCK on all tables in all SELECT statements in a transaction. This is the least restrictive of the isolation levels.
