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Transaction

A transaction is a group of operations executed as a single logical unit satisfying ACID properties — all or nothing.

Purpose

To bundle multiple operations into an atomic unit, guaranteeing correctness under failures and concurrency.

Mechanism

BEGIN starts it, operations execute, COMMIT commits or ROLLBACK aborts. Atomicity is guaranteed by the undo log, durability by the redo log/WAL, isolation by locks or MVCC. Distributed transactions use 2PC/3PC or the Saga pattern.

Use cases

  • Bank transfers
  • Orders and inventory deduction
  • Multi-table relational updates
  • Distributed cross-service operations

Examples

  • Input 
    BEGIN; A→B 100; COMMIT
    Output 
    Atomic transfer

    All or nothing

Common errors

No explicit transaction causes partial commits
Wrap related operations in a transaction

Related terms

ACID
ACID is the four properties of relational transactions: atomicity (all or nothing), consistency (constraints preserved), isolation (concurrency without interference), and durability (committed data is never lost).
GLOSSARY
Isolation Level
Isolation levels define visibility between concurrent transactions, from read uncommitted to serializable; higher levels give stronger consistency but lower concurrency.
GLOSSARY
Primary Key
A primary key is the column or column combination that uniquely identifies each row in a table — non-null and unique; the row identity.
GLOSSARY

References