Timestamp-based Concurrency Control - Recoverability

Recoverability

For an explanation of the terms recoverable (RC), avoids cascading aborts (ACA) and strict (ST) see Schedule (computer science).

Note that timestamp ordering in its basic form does not produce recoverable histories. Consider for example the following history with transactions and :

This could be produced by a TO scheduler, but is not recoverable, as commits even though having read from an uncomitted transaction. To make sure the it produces recoverable histories, a scheduler can keep a list of other transactions each transaction has read from, and not let a transaction commit before this list consisted of only committed transactions. To avoid cascading aborts, the scheduler could tag data written by uncommitted transactions as dirty, and never let a read operation commence on such a data item before it was untagged. To get a strict history, the scheduler should not allow any operations on dirty items.