Atomicity, Consistency, Isolation, Durability (ACID)

ACID (Atomicity, Consistency, Isolation, Durability) describes the fundamental properties of reliable database systems.

• Atomicity: Ensure DB transactions are treated as a single, indivisible unit.
  • Either all operations are completed successfully, or none of them are
  • If a transaction fails, the DB is left in same state as before
• Consistency: Ensure DB remains in valid state before and after a transaction.
  • DB disallows a transaction if it violates any integrity constraints
  • E.g. a transaction inserting a duplicate record should be rejected
• Isolation: Ensure concurrent transactions do not interfere with each other.
  • Each transaction is executed as if it were the only transaction occurring
  • Prevents inconsistent results due to race conditions
• Durability: Ensure committed transactions remain committed
  • Changes are permanently stored in the DB
  • System failures can be recovered from