Alternative correctness criteria for multiversion concurrency control and a locking protocol via freezing

Concurrency control protocols based on multiversions have been used in some commercial transaction processing systems in order to provide the serializable executions of transactions. In the existing protocols, transactions are allowed to read only the most recent version of each data item in order to ensure the correct execution of transactions. However this feature is not desirable in some advanced database systems which have more requirements such as timing or security constraints besides serializability. We propose a new correctness criteria, called F-serializability, for multiversion concurrency control protocols. It is the extended definition of 'l-serial' and relaxes the condition so that a protocol provides not only the most recent version but also the previous one to transactions, if necessary. We prove that whenever a multiversion schedule is F-serializable, the schedule is also one-copy serializable. This is the first contribution of our paper. Next, we propose a new concurrency control protocol for multilevel secure (MLS) database systems which guarantees the proposed serializability. In an MLS database system, a transaction scheduler must satisfy security constraints as well as ensure the serializable execution of transactions.