Technical Interview Questions » Ms Sql Server Interview Questions

What is Isolation Level?

admin — Thu, 15 Mar 2007 11:30:35 +0000

An isolation level determines the degree of isolation of data between concurrent transactions. The default SQL Server isolation level is Read Committed. A lower isolation level increases concurrency, but at the expense of data correctness. Conversely, a higher isolation level ensures that data is correct, but can affect concurrency negatively. The isolation level required by an application determines the locking behavior SQL Server uses. SQL-92 defines the following isolation levels, all of which are supported by SQL Server:

Read uncommitted (the lowest level where transactions are isolated only enough to ensure that physically corrupt data is not read).

Read committed (SQL Server default level). Repeatable read. Serializable (the highest level, where transactions are completely isolated from one another).

What is Transaction?

admin — Thu, 15 Mar 2007 11:29:40 +0000

A transaction is a sequence of operations performed as a single logical unit of work. A logical unit of work must exhibit four properties, called the ACID (Atomicity, Consistency, Isolation, and Durability) properties, to qualify as a transaction.

What are the constraints?

admin — Thu, 15 Mar 2007 11:29:20 +0000

Table Constraints define rules regarding the values allowed in columns and are the standard mechanism for enforcing integrity. SQL Server 2000 supports five classes of constraints. NOT NULL , CHECK, UNIQUE, PRIMARY KEY, FOREIGN KEY.

What are defaults? Is there a column to which a default can’t be bound?

admin — Thu, 15 Mar 2007 11:28:09 +0000

A default is a value that will be used by a column, if no value is supplied to that column while inserting data. IDENTITY columns and timestamp columns can’t have defaults bound to them.

What is DTS?

admin — Thu, 15 Mar 2007 11:27:49 +0000

Microsoft® SQL Server™ 2000 Data Transformation Services (DTS) is a set of graphical tools and programmable objects that lets you extract, transform, and consolidate data from disparate sources into single or multiple destinations.

What is DTC?

admin — Thu, 15 Mar 2007 11:27:29 +0000

The Microsoft Distributed Transaction Coordinator (MS DTC) is a transaction manager that allows client applications to include several different sources of data in one transaction. MS DTC coordinates committing the distributed transaction across all the servers enlisted in the transaction.

Does SQL Server 2000 clustering support load balancing?

admin — Thu, 15 Mar 2007 11:26:54 +0000

SQL Server 2000 clustering does not provide load balancing; it provides failover support. To achieve load balancing, you need software that balances the load between clusters, not between servers within a cluster.

How to restart SQL Server in single user mode?

admin — Thu, 15 Mar 2007 11:26:35 +0000

From Startup Options :- Go to SQL Server Properties by right-clicking on the Server name in the Enterprise manager. Under the ‘General’ tab, click on ‘Startup Parameters’. Enter a value of -m in the Parameter.

What is a LiveLock?

admin — Thu, 15 Mar 2007 11:26:12 +0000

A livelock is one, where a request for an exclusive lock is repeatedly denied because a series of overlapping shared locks keeps interfering. SQL Server detects the situation after four denials and refuses further shared locks. A livelock also occurs when read transactions monopolize a table or page, forcing a write transaction to wait indefinitely.

What is a deadlock?

admin — Thu, 15 Mar 2007 11:25:54 +0000

Deadlock is a situation when two processes, each having a lock on one piece of data, attempt to acquire a lock on the other’s piece. Each process would wait indefinitely for the other to release the lock, unless one of the user processes is terminated. SQL Server detects deadlocks and terminates one user’s process.