Serializability problems of interleaved database transactions

Abstract

The interleaved execution of database transactions produces correctness problems. It is called correct — or serializable —, if it is equivalent to a serial execution of the same transactions. An execution of a set of transactions is described by the sequence of the read/write actions — called schedule —, a reads-from rolation ϕ and an overwrite relation ω.

A database model is assumed, in which old values of the variables are still available. In this environment for a given schedule there exist a set of possible reads-from relations φ and a set of possible overwrite relations ω.

Three serializability problems are formulated and discussed:

• 1. For a given schedule x, does there exist ϕ_Oεφ, ω _Oεω, such that the execution described by (x,ϕ_O,ω _O) is serializable?

• 2. For a given schedule x and given ϕ_Oεφ, does there exist a ω _Oεω, such that the execution described by (x,ϕ_O,ω _O) is serializable?

• 3. For a given schedule x and given ω _Oεω, does there exist a ϕ_Oεφ, such that the execution described by (x,ϕ_O,ω _O) is serializable?