DATA MANIPULATION and CONTROL
1. What are DCL commands used for?
DCL commands are used to handle transactions and permissions. Also DCL helps you provide intrinsic security mechanism using SQL. These mechanisms protect the data stored in a database from being accessed by unauthorized users.
2. What is the deadlock?
The state in, which two or more transactions try to access same resource simultaneously.
3. What are the Concurrency Control Techniques?
The format and sequence of message exchange between two communicating entities is called a Protocol. To ensure mutual exclusion between two or more transactions is necessary to apply concurrency control techniques such as:
· Lock-based protocol
· Deadlock-handling protocol
· Timestamp-ordering protocol
· Validation protocol.
4. What are the various properties of transactions?
· Atomicity – refers to the state of the database in which a transaction is either complete or has not started
· Consistency – ensures that the execution of transactions maintains consistency in a database
· Isolation – ensures that a particular transaction is executed in isolation of other transactions, that is, data modified by a transaction must be isolated from the modification of other transactions
· Durability – ensures that after a transaction is successfully completed, the changes made to the database do not revert, even after a system failure.
5. What are the storage devices used to store the data based on
the volatile and non-volatile storage structures?
· Volatile storage – this type of storage medium is relatively fast and includes the cache memory and the main memory. You can quickly access data items from a volatile storage medium. However, the data that resides in a volatile storage medium cannot survive system crashes.
· Non-volatile storage – this type of storage medium includes disks and magnetic tapes. You can use disks to store the data items online and tapes for archiving. However, both disks and tape drives may be subject to failures resulting in loss of data.
6. Can a transaction failure due to a logical or a system error?
Yes.
7. Which of the protocols allows you to apply a lock on data
item?
Lock-based protocols.
8. Can
the lost update problem occur when a transaction tries to update a data-item
value?
No, the lost update problem occurs when the data written by one transaction is overwritten by another transaction.
10.
What is the ACID properties of a transaction?
A transaction consists of certain characteristic collectively called ACID properties, which is an acronym for: Atomicity, Consistency, Isolation, Durability.
No, the deadlock detection-and-recovery method allows a system to recover from a deadlock state.
Validation protocol.
