Nested transactions with integrity constraints

This paper presents a solution to check integrity constraints in database systems supporting nested transactions. Using nested transactions allows to introduce parallelism inside a transaction and to partially recover failing transactions by defining a hierarchy of sub-transactions. If a constraint is violated by some sub-trans actions, it is possible to reach the validation of the nested transaction, even if some part of it had to be aborted. In our solution, (i) only constraints that might be violated are checked, (ii) constraints are checked as soon as possible during the execution of the nested transaction and (iii) as few sub-transactions as possible are aborted. We do not interfere with the execution control of nested transactions and users do not have to add any control code in the definition of constraints or of transactions. The main idea of our solution is to attach the checking of a constraint to the smallest common ancestor of the sub-transactions which could violate the constraint.