Transactions - What's it all about?

• Far more than just locking

• The A.C.I.D. test

• True transactions give true safety

  • even from power failures and system crashes!
  • Incomplete transactions are automatically rolled-back by the database server when it's restarted.

• Also removes burden of undoing incomplete changes

• Hard to implement (for the vendor) and has significant performance cost

• A very large topic worthy of an entire tutorial

Previous slide

Next slide

Back to first slide

View graphic version

ACID:

Atomicity - all or nothing.

Consistency - database stays consistent, no violations of constraints.

Isolation - each transaction executes as if done serially.

Durability - once the transaction completes, the changes will persist.

ACID properties are implemented by concurrency controls and recovery mechanisms.