Suppose that a DBMS recognizes increment, which increments an in- teger-valued object by 1, and decrement as actions, in addition to reads and writes. A transaction that increments an object need not know the value of the object; incre- ment and decrement are versions of blind writes. In addition to shared and exclusive locks, two special locks are supported: An object must be locked in I mode before incrementing it and locked in D mode before decrementing it. An I lock is compatible with another I or D lock on the same object, but not with S and X locks. 1. Illustrate how the use of I and D locks can increase concurrency. (Show a schedule allowed by Strict 2PL that only uses S and X locks. Explain how the use of I and D locks can allow more actions to be interleaved, while continuing to follow Strict 2PL.) 2. Informally explain how Strict 2PL guarantees serializability even in the presence of I and D locks. (Identify which pairs of actions conflict, in the sense that their relative order can affect the result, and show that the use of S, X, I, and D locks according to Strict 2PL orders all conflicting pairs of actions to be the same as the order in some serial schedule.)

Suppose that a DBMS recognizes increment, which increments an in- teger-valued object by 1, and decrement as actions, in addition to reads and writes. A transaction that increments an object need not know the value of the object; incre- ment and decrement are versions of blind writes. In addition to shared and exclusive locks, two special locks are supported: An object must be locked in I mode before incrementing it and locked in D mode before decrementing it. An I lock is compatible with another I or D lock on the same object, but not with S and X locks. 1. Illustrate how the use of I and D locks can increase concurrency. (Show a schedule allowed by Strict 2PL that only uses S and X locks. Explain how the use of I and D locks can allow more actions to be interleaved, while continuing to follow Strict 2PL.) 2. Informally explain how Strict 2PL guarantees serializability even in the presence of I and D locks. (Identify which pairs of actions conflict, in the sense that their relative order can affect the result, and show that the use of S, X, I, and D locks according to Strict 2PL orders all conflicting pairs of actions to be the same as the order in some serial schedule.)

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Concept explainers

Types of database architectures

A Database Architecture represents the Database Management System’s (DBMS) design (schema). The DBMS architecture makes it easy to understand the components involved in the database system and their relations. The DBMS architecture may vary based on the system on which it runs. Some systems contain both client and server machines whereas some run only on a server machine. Based on the architecture, the system can be classified as centralized, decentralized, or hierarchical.

Question

Suppose that a DBMS recognizes increment, which increments an in-
teger-valued object by 1, and decrement as actions, in addition to reads and writes.
A transaction that increments an object need not know the value of the object; incre-
ment and decrement are versions of blind writes. In addition to shared and exclusive
locks, two special locks are supported: An object must be locked in I mode before
incrementing it and locked in D mode before decrementing it. An I lock is compatible
with another I or D lock on the same object, but not with S and X locks.
1. Illustrate how the use of I and D locks can increase concurrency. (Show a schedule
allowed by Strict 2PL that only uses S and X locks. Explain how the use of I
and D locks can allow more actions to be interleaved, while continuing to follow
Strict 2PL.)
2. Informally explain how Strict 2PL guarantees serializability even in the presence
of I and D locks. (Identify which pairs of actions conflict, in the sense that their
relative order can affect the result, and show that the use of S, X, I, and D locks
according to Strict 2PL orders all conflicting pairs of actions to be the same as
the order in some serial schedule.)

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