Technical Interview Questions and Answers :: Wipro
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- Atomicity âˆ’ This property states that a transaction must be treated as an atomic unit, that is, either all of its operations are executed or none. There must be no state in a database where a transaction is left partially completed. States should be defined either before the execution of the transaction or after the execution/abortion/failure of the transaction.
- Consistency âˆ’ The database must remain in a consistent state after any transaction. No transaction should have any adverse effect on the data residing in the database. If the database was in a consistent state before the execution of a transaction, it must remain consistent after the execution of the transaction as well.
- Durability âˆ’ The database should be durable enough to hold all its latest updates even if the system fails or restarts. If a transaction updates a chunk of data in a database and commits, then the database will hold the modified data. If a transaction commits but the system fails before the data could be written on to the disk, then that data will be updated once the system springs back into action.
- Isolation âˆ’ In a database system where more than one transaction are being executed simultaneously and in parallel, the property of isolation states that all the transactions will be carried out and executed as if it is the only transaction in the system. No transaction will affect the existence of any other transaction.
A transaction is a very small unit of a program and it may contain several lowlevel tasks. A transaction in a database system must maintain Atomicity, Consistency, Isolation, and Durability âˆ’ commonly known as ACID properties âˆ’ in order to ensure accuracy, completeness, and data integrity.
ACID properties are 4 important properties of a transaction that a DBMS must ensure to maintain data in the case of concurrent access
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osi model means( open system interconnection) .it has seven layers 1.physical layer 2.data link layer 3.network layer 4. transport layer 5. session layer 6.presentation layer 7. application layer