Imagine transferring $100 from Account A to Account B.

Two operations must happen:

Subtract $100 from A Add $100 to B

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What happens if the first succeeds but the second fails?

Money disappears.

This is where database transactions become important.

What Is a Transaction?

A transaction groups multiple database operations into a logical unit.

Conceptually:

BEGIN

Subtract money from A Add money to B

COMMIT

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If something goes wrong:

ROLLBACK

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The database attempts to return to the previous consistent state.

ACID

Transactions are commonly discussed using ACID:

Atomicity

All operations succeed, or none do.

Consistency

The database moves from one valid state to another.

Isolation

Concurrent transactions shouldn't incorrectly interfere with one another.

Durability

Committed changes should survive failures according to the database's guarantees.

Why Transactions…