Concurrency Control for Perceivedly Instantaneous Transactions in Valid-Time Databases

Although temporal databases have received considerable at tent ion as a topic for research, little work in the area has paid at tent ion t o the concurrency control mechanisms that might be employed in temporal databases. This paper describes how the not ion of the current time also called ‘now’ i n valid-time databases can cause standard serialisation theory t o give what are a t least unintuitiue results, if n o t actually incorrect results. T h e paper t h e n describes two modifications t o standard serialisation theory which correct the behaviour t o give what we t e r m perceivably instantaneous transactions: transactions where serialising TI and Tz as [Tl,Tz] always implies that the current t i m e seen b y TI is less than or equal t o the current t i m e seen b y Tz.