Transaction States

Transactions have four states: active, committed, limbo, and rolled back.

Taking these cases in order from the least complex to the most:

Limbo: A transaction that started a two-phase commit by calling the Prepare routine. The transaction may be alive or not. At any point, the transaction may re-appear and ask to commit or rollback. Changes it made can neither be trusted nor ignored, and certainly cannot be removed from the database.

Committed: A transaction is which completed its activity successfully. Either A) it called Commit and the commit completed successfully, or B) it called Rollback but made no changes to the database, or C) it called Rollback and its changes were subsequently undone and its state changed to Committed. This transaction is finished and will never be heard from again, and its remaining changes are now officially part of the database.

Rolled back: A transaction which either: A) called Rollback and requested that its changes be removed from the database, or B) never called Commit so was marked as Active, but discovered to be dead by another transaction which marked it as rolled back. In either case, changes made by this transaction must be ignored and should be removed from the database.

Active: A transaction which: A) hasn't started. B) has started and hasn't finished. C) started and ended without calling any termination routine. (e.g. crashed, lost communication, etc.)

Taken from IBPhoenix