The database eliminates T1's effects, and T2 sees only valid data.An integrity constraint requires that the value in A and the value in B must sum to 100.

5 Briefly, in the first phase, one node (the coordinator) interrogates the other nodes (the participants) and only when all reply that they are prepared does the coordinator, in the second phase, formalize the transaction.He drank acid instead of brandy.Ashes insoluble in acid must not exceed 1 g/kg.

An alternative to locking is multiversion concurrency control, in which the database provides each reading transaction the prior, unmodified version of data that is being modified by another active transaction.Another example would be with integrity constraints, which would not allow us to delete a row in one table whose Primary key is referred to by at least one foreign key in other tables.