Serializability And Recoverability

Serializability

Serializability is the classical concurrency scheme. This helps to ensures that a schedule with regard to performing executing concurrent transactions is equivalent to one that executes the transactions serially in some order. It assumes that all accesses towards the database are done using read and write operations. A schedule is known as correct if we can find a serial schedule that is equivalent to it.

Read-Write Synchronization:

If a transaction reads a value written by an additional transaction in single schedule, then it also does so in the other schedule.

Write-Write Synchronization:

If a transaction overwrites the value of an additional transaction in single schedule, it also does so in the other schedule. Both of these properties make sure that there can be no difference in the effects of the two schedules.

Recoverability

Serializability recognizes schedules which preserve database consistency, assuming no transaction fails. Could also examine recoverability of transaction within schedules. If transaction fails, atomicity requires effect of transaction to be undone. Durability states that once transaction commits, its change cannot be undone (without running another, compensating, transaction).

Recoverable Schedule

A schedules exactly where, for every set of transaction Ti and Tj. If Tj reads a data items previously written by Ti, then the commit operation of Ti precedes the commit operation of Tj.