ACID Transactions

Abstract

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• Transaction that is Atomic, Consistent, Isolation & Durable
• Usually achieved with Lock

Benefits

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• Ensure Data never falls into an inconsistent state because of an Transaction that only partially completes
• Guarantees that a READ will return the latest successful WRITE

Cons

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• Costly
• Difficult to scale

Terminologies

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Atomic

• A quality that ensures each Transaction is fully committed or not at all
• It treats each Transaction as a single unit of change to Database and can’t be partially completed
• Transaction is either committed or rolled back

Consistent

• A quality that ensures the Database is in a consistent and valid state after a Transaction is committed
• It prevents the Database from being corrupted

Isolation

• Ensures that Transaction are independent
• Each Transaction can occur as though they were occurring one by one, even though they’re actually occurring simultaneously
• Ensures that data is managed between database operations so it is not used in Transaction simultaneously. Instead, the first transaction will complete, and then the next will begin

Durable

• Permanently preserves all Transaction by saving to permanent storage, not kept in volatile memory
• Ensures changes to data made by successfully executed Transaction will be saved, even in the event of system failure (like power loss)