Definition

A transaction in DBMS is a finite sequence of database operations that is executed as one logical unit of work, meaning either all operations are performed successfully or none are performed.

-- Example for "logical unite of work"
Read(A)
A = A − 100
Write(A)
Read(B)
B = B + 100
Write(B)
Commit

A transaction must satisfy the ACID properties to ensure database correctness and consistency.

Image Description

Key Points

  • A transaction groups multiple database operations into a single logical task
  • Partial execution is not allowed
  • Failure of any operation causes the entire transaction to rollback
  • Ensures reliability in concurrent and failure-prone environments

ACID Properties (Overview)

  • Atomicity – All operations execute or none execute
  • Consistency – Database remains in a valid state
  • Isolation – Transactions do not interfere with each other
  • Durability – Committed changes persist permanently

Schedule

A schedule is the execution order of operations of multiple transactions on the same database, possibly executed concurrently.