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

Abstract

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.In this paper; we propose a new correctness criteria, called F-serializability, for multiversion concurrency control protocols. It is the extended dejnition of 'I -serial' and relaxes the condition so that a protocol provides not only the most recent version but also the previous one to transactions, if necessaiy. We prove that whenever a multiversion schedule is F-serializable, the schedule is also one-copy serializable. This is the$rst contribution of sur papel: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 satish security constraints as well as ensure the serializable execution of transactions. Our protocol produces one-copy serializable schedules without covert channels. In addition, the proposed protocol removes the starvations of high level transactions. Our protocol is based on multiversion two phase locking(MV2PL) but a new method, namely freezing method, is additionally used in order to satisfy security requirements. Since 'F-serial' is more general than 'I-serial', our protocol can provide a higher degree of concurrency than MV2PL which is based on 'I-serial'. This is the second contribution of our papel: