Schedule

Question 1

What is schedule?
1.Serial Schedule
2.Non-Serial Schedule
3.Eqivalent Schedule

Answer 1

process of grouping transaction into one and then executing then in a order.

A schedule is the chronological (sequential) order in which instructions are executed in a
system.

Question 2

Why is schedule required?

Answer 2

A schedule is required in a database because some transaction occur in parallel, they may affect the result of transaction.

Question 3

Serial Schedule.

Answer 3

A schedule in which ongoing transaction is first completed and then other transaction is started.

Question 4

Non-Serial Schedule

Answer 4

2nd Transaction starts before 1st one ends

Question 5

Equivalent Schedule.

Answer 5

If two schedules produce the same result after execution.

Question 6

Problems due to concurrent execution.

Answer 6

1.Dirty Read
2.Unrepeatable Read problem
3.phantom read problem
4.Lost update problem

Question 7

Dirty Read Problem.

Answer 7

If a transaction starts and reads A and does A=A-50 then write A. and then another transaction starts with taking this A value but due to some reason the first transaction fails. So the value of A picked in 2nd Transaction will be dirty read.

Question 8

Unrepeatable read problem

Answer 8

reading the same variable (A)
more than one time and getting
different values due to parallel going to transaction.

Question 9

Phantom Read problem

Answer 9

Reading a variable which is deleted in parent transaction.