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# Calculation of Serial and Non-Serial Schedules in DBMS

• Last Updated : 15 Feb, 2021

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

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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