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Chapter 17: Problem 9

What is a serial schedule? What is a serializable schedule? Why is a serial schedule considered correct? Why is a serializable schedule considered correct?

Short Answer

Expert verified
A Serial Schedule is a type of schedule where transactions are executed one after another, whilst a Serializable Schedule results in the same database state as a Serial Schedule, even with concurrent operations. Serial schedules are correct as they avoid conflicts and issues associated with concurrent operations, thereby preserving the consistency of the database. Serializable schedules, on the other hand, maintain consistency and conflict-freeness by keeping the same sequencing of operations as in serial schedules, despite potential overlaps in transactions, therefore they are also considered correct.

Step by step solution

01

Understanding Serial Schedule

A Serial Schedule refers to a kind of schedule in which the transactions are arranged in a manner where the operation(s) of one transaction are executed before the operation(s) of the next transaction. In simpler terms, in a serial schedule, transactions are not overlapped; they're executed one after the other.
02

Understanding Serializable Schedule

A Serializable Schedule is a schedule in which the state after all transactions are executed is the same as the state that would have resulted if the transactions had been executed in serial order. In other words, a schedule is serializable if it is equivalent to a serial schedule as far as the end result is concerned. There are two types of serializability: conflict and view serializability. Conflict serializability considers the conflict between read and write operations, whereas view serializability views the schedule as a collection of actions (read, write, etc).
03

Why Serial Schedule is considered correct?

A serial schedule is considered correct as it preserves the consistency of a Database and doesn't cause any conflicts. The challenges associated with concurrent transaction execution, such as Dirty Read, Non-Repeatable Read, or Phantom Read, are avoided in a Serial Schedule since transactions are executed in an ordered manner, adhering to the isolation property in ACID (Atomicity, Consistency, Isolation, Durability) database properties.
04

Why Serializable Schedule is considered correct?

A Serializable Schedule is considered correct because it gives the same outcome as a Serial Schedule, even though transactions may execute concurrent operations. It is designed in a way that it maintains the same sequencing of read and write operations in each transaction, and there is no disruption in data integrity. Hence, the database state remains consistent and free of conflicts, fulfilling the ACID properties.

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Most popular questions from this chapter

Consider schedules \(S_{3}, S_{4},\) and \(S_{5}\) below. Determine whether each schedule is strict, cascadeless, recoverable, or nonrecoverable. (Determine the strictest recoverability condition that each schedule satisfies.) $$\begin{array}{l} S_{3}: r_{1}(X) ; r_{2}(Z) ; r_{1}(Z) ; r_{3}(X) ; r_{3}(Y) ; w_{1}(X) ; c_{1} ; w_{3}(Y) ; c_{3} ; r_{2}(Y) ; w_{2}(Z) ; w_{2}(Y) ; c_{2} \\ S_{4}: r_{1}(X) ; r_{2}(Z) ; r_{1}(Z) ; r_{3}(X) ; r_{3}(Y) ; w_{1}(X) ; w_{3}(Y) ; r_{2}(Y) ; w_{2}(Z) ; w_{2}(Y) ; c_{1} ; c_{2} ; c_{3} \\ S_{5}: r_{1}(X) ; r_{2}(Z) ; r_{3}(X) ; r_{1}(Z) ; r_{2}(Y) ; r_{3}(Y) ; w_{1}(X) ; c_{1} ; w_{2}(Z) ; w_{3}(Y) ; w_{2}(Y) ; c_{3} ; c_{2} \end{array}$$

Describe the four levels of isolation in SQL.

Define the violations caused by each of the following: dirty read, nonrepeatable read, and phantoms.

What is meant by the concurrent execution of database transactions in a multiuser system? Discuss why concurrency control is needed, and give informal examples.

Discuss how serializability is used to enforce concurrency control in a database system. Why is serializability sometimes considered too restrictive as a measure of correctness for schedules?
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