All categories

3 years ago

1. What is concurrency control? State and explain the different issues that may arise in the absence of concurrency control.

Computers and Technology

1 answer:

user100 [1]3 years ago

5 0

Answer:

1. Concurrency control is the process of managing simultaneous execution of transactions in a multiprocessing database system without having them interfere with one another. The transactions could mean different operation like queries, updates, inserts, deletes and so on.

Issues that may arise in the absence of concurrency control are:

a) The Lost update problem

b) The Temporary update (or dirty read) problem

c) The Incorrect summary problem

d) The Unrepeatable read problem

The Lost update problem: This problem occurs when two transactions that access the same database items have their operations interleaved in a way that makes the value of some database items incorrect.

The Temporary update (or dirty read) problem: This problem occurs when one transaction updates a database item and then the transaction fails for some reason. Meanwhile, the updated item is accessed (read) by another transaction before it is changed back (or rolled back) to its original value. This problem is also known as the dirty read problem.

The Incorrect summary problem: This problem occur if one transaction is calculating an aggregate summary function on a number of database items while other transactions are updating some of these items, the aggregate function may calculate some values before they are updated and others after they are updated.

The Unrepeatable Read Problem. This problem occur where a transaction T reads the same item twice and the item is changed by another transaction T′ between the two reads. Hence, T receives different values for its two reads of the same item.

2. The different techniques to achieve concurrency control are categorized into:

a) Lock-based protocol

b) Timestamp-based protocol

Lock-based protocol: Those database systems that are prepared with the concept of lock-based protocols employ a mechanism where any transaction cannot read or write data until it gains a suitable lock on it.

Timestamp-based Protocol: It is the most frequently used concurrency protocol is the timestamp based protocol. This protocol uses either system time or logical counter as a timestamp.

Explanation:

You might be interested in

Harmful programs used to disrupt computer operation, gather sensitive information, or gain unauthorized access to computer syste

Galina-37 [17]

Answer:

Malware

Explanation:

malware is used to disrupt computer operation, gather personal info, and or gain access to private computer systems.

6 0

3 years ago

Write a one-line program to output the following haiku.

Serggg [28]

10 CLEAR: PRINT "A lightning flash: between the forest trees I have seen water.": END

8 0

3 years ago

Read 2 more answers

Change 'What do they do' into passive voice

Ivan

What they do is the answer

7 0

4 years ago

Read 2 more answers

Universal Containers has strict security model enforced through object, field, and row-based security mechanisms. The Architect

PIT_PIT [208]

Answer:

Option A, B, and E is the correct options to the following question.

Explanation:

In the following question, some details are missing that is options of the question,

Because the Universal Containers is the corporation which wants to secure their security model that is tested through the using of the Apex automated test i.e., the platform that allow user to test due to secure their security model. So, that's why they follow the following considerations is true for testing the security model.

8 0

3 years ago

Which of these statements is true?

olchik [2.2K]

Answer:

thanks for points ☺

Explanation:

TRB Special Report 263 - Future Flight: A Review of the Small Aircraft Transportation System Concept reviews the plausibility and desirability of the SATS concept, giving special consideration to whether its potential net benefits--from user benefits to overall environmental and safety effects--are sufficiently promising to warrant public-sector investment in SATS development and deployment.

The Small Aircraft Transportation System (SATS) program has been established by the Office of Aerospace Technology in the National Aeronautics and Space Administration (NASA). In the initial 5-year phase of the program, NASA is working with the private sector and university researchers, as well as other federal and state governmental agencies, to further various aircraft-based technologies that will increase the safety and utility of operations at small airports, allow more dependable use of small airports, and improve the ability of single-piloted aircraft to operate safely in complex airspace. Guiding this program is a longer-range SATS vision of the routine use of advanced, small fixed-wing aircraft for personal transportation between communities.

The Small Aircraft Transportation System (SATS) is envisioned as relying on increasingly sophisticated and affordable small aircraft flying between small airports in lightly used airspace. The system was proposed to provide a growing share of the nation’s intercity personal and business travel. The development of such a system was considered to be justified by the potential to ease congestion in the existing aviation system and on highways serving densely traveled intercity markets. Without attempting to prejudge how advances in general aviation technology might evolve and affect travel markets, the committee that examined the SATS concept concluded that the concept is problematic in several ways as a vision to guide NASA’s technology development. Although the cost of small jet engines developed in partnership with NASA could drop dramatically, small jets would still be well beyond the means of all but the wealthiest members of society. The aircraft might be adopted by firms offering air taxi service, but the cost of such service would likely remain steep; therefore, sufficient market penetration to relieve congestion at hub airports would be unlikely. Moreover, the origins and destinations of most business travelers are major population centers, making travel to and from remote general aviation airports unappealing. The cost to upgrade such airports would be substantial as well, even assuming that SATS aircraft would have onboard technologies that would reduce the need for airport radars, precision landing guides, and air traffic control. The environmental consequences could also be substantial—particularly an increase in aircraft noise in rural areas unaccustomed to such intrusions. Perhaps the most difficult issues to address would be public concerns about safety. Finally, the use of SATS aircraft in and around major metropolitan areas would complicate an already overstressed air traffic control system, and the human factors issues of increased automation for relatively inexperienced pilots are far from being resolved.

For all of the above reasons, the committee did not endorse the SATS concept as a guide for NASA R&D. The committee noted, however, that NASA’s support for ongoing technology development in general aviation is welcome and needed. General aviation has a much worse safety record than commercial aviation. The committee recommended that NASA work with other federal agencies, such as USDOT, the Federal Aviation Administration, and the National Transportation Safety Board in defining and pursuing opportunities to advance and improve general aviation.

4 0

3 years ago