Calculation of Serial and Non-Serial Schedules in DBMS

The serial execution of a transaction is defined as Schedule. It is made up of a number of transactions each comprising of a number of instructions.

Types of Schedules

  • Serial Schedules
  • Non-Serial Schedules

Calculation of Number of Schedules :
Consider there to be N number of transactions t1, t2, t3, …., tN with k1, k2, k3, ….., kN number of operations respectively.

  1. Total Number of Schedules –
    (N1 + N2 + N3 + ..... + Nn)! / (N1! * N2! * N3! * ... * Nn!)
  2. Number of Serial Schedules –
    It is all possible permutations of n transactions = N!
  3. Number of Non-Serial Schedules –
    Total Schedules = Serial Schedules + Non-Serial Schedules
    Number of Non-Serial Schedules = Total Number of Schedules – Number of Serial Schedules

    N! - ((N1 + N2 + N3 + ..... + Nn)! / (N1! * N2! * N3! * ... * Nn!))



Example –
Consider there to be three transactions with 1, 2, and 3 operations respectively.
We have to find –

  • Total number of schedules possible.
  • Total number of serial schedules and non-serial schedules possible.

Solution –
Total Number of Schedules,

= (1 + 2 + 3)! / (1! + 2! + 3!) = 6! / 9 = 120

Number of Serial Schedules,
= 3! = 6

Number of Non-Serial Schedules,
= Total Number of Schedules - Number of Serial Schedules 
= 120 - 6 
= 114 

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