What is ACID?

In database world, ACID is an acronym. It stands for; Atomicity, Consistency, Isolation and Durability. Databases should have these four features for them to become a reliable databases. All of these four features relate with transactions.

• Atomicity:
  A transaction has to be completely commited or roll-backed, a portion of the transaction should not be committed to the database due to any issue even on a hardware failure.
  
• Consistancy:
  After any transaction the data in the database should be correct and vailid according to the requirements. Database should not be having any illegal data after a transaction.
  
• Isolation:
  When two or more transactions exists, one's behaviour should not give invalid data for the other transaction. That is, when one transaction is in progress, the data alterations made by that transaction should not be visible to any other transactions.
  
• Durability:
  After the commit operation is aknowledged by the database, the data inside that transaction should not be lost. The updating of those data into the database has to be guaranteed.
  

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