KS3 Computer Science

11-14 Years Old

48 modules covering EVERY Computer Science topic needed for KS3 level.

GCSE Computer Science

14-16 Years Old

45 modules covering EVERY Computer Science topic needed for GCSE level.

A-Level Computer Science

16-18 Years Old

66 modules covering EVERY Computer Science topic needed for A-Level.

GCSE Databases Resources (14-16 years)

  • An editable PowerPoint lesson presentation
  • Editable revision handouts
  • A glossary which covers the key terminologies of the module
  • Topic mindmaps for visualising the key concepts
  • Printable flashcards to help students engage active recall and confidence-based repetition
  • A quiz with accompanying answer key to test knowledge and understanding of the module

A-Level Transaction Processing & ACID (16-18 years)

  • An editable PowerPoint lesson presentation
  • Editable revision handouts
  • A glossary which covers the key terminologies of the module
  • Topic mindmaps for visualising the key concepts
  • Printable flashcards to help students engage active recall and confidence-based repetition
  • A quiz with accompanying answer key to test knowledge and understanding of the module

What is ACID

In digital engineering, in terms of blunders, control disappointments, and multiple injuries, ACID (atomicity, accuracy, seclusion, toughness) is a number of properties of knowledge base exchanges required to guarantee data legitimacy. A sequence of data set operations satisfying the ACID properties (which can be used as a solitary coherent information procedure) is regarded as an exchange with respect to information bases.

For example, a solitary transaction is a transaction of assets beginning with one ledger and then on to the next, including numerous modifications, such as costing one record and crediting another.

Illustration example of ACID

I don’t believe it’s an exaggeration to state that information is pretty significant. Information is particularly significant for present day associations. Truth be told, The Economist ventured to such an extreme as to state that information has outperformed oil as the world’s most significant asset, and that it will return in 2017.

One of the issues with information is the huge measures of it that should be prepared consistently. There’s so much information flying over the globe nowadays that we need to think of another term just to communicate how much information there is: enormous information. Without a doubt, it’s not the most amazing sounding term out there, but rather the reality remains.

With this huge information out there, associations are looking for approaches to improve how they oversee everything from a common sense, computational, and security angle. Like Spiderman’s Uncle Ben once stated, “With extraordinary [data] comes incredible duty.” The best technique the IT world has made for exploring the complexities of information the board is using data sets.

What is database

I don’t believe it’s an exaggeration to state that information is pretty significant. Information is Databases are organised arrangements of information that are put away inside PCs. Intermittently, information bases are put away on whole worker ranches loaded up with PCs that were made explicitly to deal with that information and the cycles vital for utilising it.

Present day information bases are such unpredictable frameworks that administration frameworks have been intended to deal with them. These information base administration frameworks (DBMS) try to upgrade and deal with the capacity and recovery of information inside data sets. One of the directing stars driving associations to fruitful information base administration is the ACID methodology.

What is Atomicity

With regards to information bases, atomicity implies that you either focus on the aggregate of the exchange happening or having no exchange by any means. Basically, a nuclear exchange guarantees that any submit you make completes the whole activity effectively or, in instances of the association being lost in an activity, the information base is moved back to its state preceding the submit being started.

This is significant for keeping accidents or blackouts from making situations where the exchange was somewhat completed to an obscure general state. In the event that an accident happens during an exchange with no atomicity, you can’t know precisely how far along the cycle was before the exchange was intruded. By utilising atomicity, you guarantee that either the whole exchange is effectively finished or none of it was.

Why is atomicity important?

Atomicity is significant for applications needing to refresh two related information bases (for instance, an essential information base and optional file) in a solitary legitimate activity. Quite a few procedures on quite a few information bases can be remembered for a solitary exchange to guarantee the atomicity of the activities.

What is an atomicity problem?

Atomicity is significant for applications needing to refresh two related information bases. A nuclear exchange is an unbreakable and unchangeable arrangement of data set tasks with the end goal that either all happen, or nothing happens. A promise of atomicity forestalls changes that happen mostly more to the knowledge base, which may create more notable problems than dismissing the whole arrangement inside and out.

How do you ensure atomicity?

  •  Keep different exchanges from meddling with the columns they are composing or perusing.
  • Ensure that either all or none of the progressions that the exchange makes, will be in the information base when the exchange submits.

What is Consistency?

Consistency alludes to keeping up information respectability limitations. A predictable exchange won’t disregard uprightness requirements put on the information by the information base principles. Implementing consistency will guarantee that if an information base goes into an illicit state (if an infringement of information uprightness limitations happens) the cycle will be prematurely ended and changes moved back to their past, lawful state.

Another method of guaranteeing consistency inside an information base all through every exchange is by likewise authorising revelatory limitations put on the data set. A case of a decisive requirement may be that all client accounts must have a positive equalisation. On the off chance that an exchange would bring a client account into a negative parity, that exchange would be moved back. These guarantees changes are effective at keeping information honesty or they are dropped totally.

Benefits of consistency:

  • Consistency considers estimation. Until you have taken a stab at something new for a while and in a steady way, you can’t choose if it works or not.
  •  Consistency makes responsibility.
  • Consistency constructs your notoriety.
  • Consistency renders you important.
  • Consistency protects your message.

Why is consistency important?

Consistency creates schedules and gathers speed. It structures propensities that become practically natural. Authority master John Maxwell stated: “Little teachings rehashed with consistency consistently lead to incredible accomplishments picked up gradually after some time.” Consistency is particularly significant in business.

What is good about being consistent?

Being predictable will help gather speed. This implies we’ll additionally like what we’re running after. It can quickly track your improvement or advancement in any territory. Consistency will prompt advancement, which can accelerate the achievement of what we need.

What is Isolation

Detached exchanges are viewed as “serializable”, which means every exchange occurs in an unmistakable request with no exchanges happening pair. Any peruses or composes performed on the information base won’t be affected by different peruses and composes of discrete exchanges happening on a similar data set. A worldwide request is made with every exchange queueing up in line to guarantee that the exchanges total completely before another starts.

This doesn’t mean two activities can’t occur simultaneously by any stretch of the imagination. Different exchanges can happen as long as those exchanges have no chance of affecting different exchanges happening simultaneously. Doing this can have impacts on the speed of exchanges as it might constrain numerous activities to stand by before they can start. Nonetheless, this trade off merits the additional information security gave by confinement.

Confinement can be refined using a sliding size of leniency that goes between what are called idealistic exchanges and critical exchanges. A hopeful exchange pattern expects that different exchanges will finish without pursuing or keeping in touch with a similar spot twice. With the idealistic outline, the two exchanges will be prematurely ended and retried on account of an exchange hitting a similar spot twice.

The critical exchange composition gives less freedom and will secure assets on the presumption that exchanges will affect different ones. This outcome in less prematurely ends and retries yet additionally implies that exchanges are compelled to hang tight in line for their turn all the more regularly in contrast with the hopeful exchange approach. Finding a sweet spot between these two goals is regularly where the best generally speaking outcome is found.

What is transaction isolation and why it is important?

Disconnection from trade is an essential feature of every value-based system. It manages the accuracy and culmination of data retrieved from investigations concerning customer details through other customer operations. An information base secures locks on information to keep up a significant level of confinement.

What is data isolation in databases?

information segregation: A property that determines when and how modifications are visible to other parallel clients and systems made by one action. Information honesty: alludes to the upkeep and affirmation that the information in a data set is right and reliable.

 What are the levels of isolation in SQL?

  • Peruse Uncommitted – Read Uncommitted is the most minimal disengagement level.
  • Peruse Committed – This separation level ensures that any information read is submitted right now it is perused.
  • Repeatable Read – This is the most prohibitive disengagement level.

What is Durability

The last part of the ACID way to deal with information base administration is solidness. Strength guarantees that changes made to the information base (exchanges) that are effectively dedicated will endure forever, even on account of framework disappointments. This guarantees that the information inside the information base won’t be undermined by administration blackouts, crashes, or different instances of disappointment. This is accomplished using changelogs that are referred to when information bases (or bits of the information base) are restarted.

At the point when each part of the ACID methodology is united effectively, information bases are kept up with the most extreme information respectability and security to guarantee that they can keep on offering some benefit to the association. An information base with debased information can introduce exorbitant issues because of the enormous accentuation that associations put on their information for both everyday activities just as vital investigation.

Utilising ACID properties with your information base will guarantee your information base keeps on conveying important information all through tasks.

How is durability maintained in the database?

In information base frameworks, strength is the ACID property which ensures that exchanges that have submitted will endure forever. Strength can be accomplished by flushing the exchange’s log records to non-unstable capacity before recognising duty.

What is the difference between full transaction durability and delayed transaction durability?

The deferred exchange strength has a couple of unmistakable bits of leeway over full exchange toughness. The primary preferred position is that it doesn’t have to write to circle before giving control back to the customer. In numerous information bases, keeping in touch with the circle gives a great deal of dispute.

How do you describe durability?

Sturdiness is the willingness of a physical object to remain utilitarian when faced with the challenges of ordinary operation over the lifetime of schedule, without needing drastic assistance or fix. There are a few quantities of strength that are used, including long life times, long consumption times, and the number of operating cycles.

ACID’s Consistency vs. CAP’s Consistency

CAP Theorem, first distributed in 2000, made it simpler for specialists to reason about disseminated frameworks.

“Appropriated frameworks must pick somewhere in the range of Consistency and 100% Availability within the sight of organisation Partitions. “

Lamentably, the utilisation of “Consistency” in both ACID and CAP prompted confused designers. Consistency in CAP is a more key concept that alludes to the assurance that all individuals from an appropriated framework have a mutual comprehension of the estimation of a solitary information component from a read angle. This assurance is likewise alluded to as solid consistency or linearisability. Truth be told, CAP’s consistency is better analysed against ACID’s segregation levels since both arrangements with the qualities that read tasks are permitted to see.

ACID Image 1

Then again, ACID’s consistency alludes to information uprightness ensures that guarantee the progress of the whole information base starting with one substantial state then onto the next. Such a change includes severe requirements of uprightness limitations, for example, information type adherence, invalid checks, connections, and then some. Given that a solitary ACID exchange can contact different information components whereas CAP’s consistency alludes to a solitary information component, ACID exchanges are a more grounded assurance than CAP’s consistency.

Transaction Processing in ACID

Exchange handling is a style of figuring, regularly performed by enormous worker PCs, that upholds intuitive applications. In exchange handling, work is partitioned into individual, unified activities, called exchanges. Paradoxically, cluster handling is a style of figuring where at least one project measures a progression of records (a clump) with almost no activity from the client or administrator.

An exchange preparing framework permits application developers to focus on composing code that underpins the business, by protecting application programs from the subtleties of exchange the executives:

  •  It deals with the simultaneous handling of exchanges.
  •  It empowers the sharing of information.
  • It guarantees the honesty of information.
  • It deals with the prioritisation of exchange execution.

CICS runs a program that is connected to the exchange at the stage where an exchange starts loading. Over the course of the exchange, this software will transfer power to multiple initiatives, making it conceivable to amass determined applications consisting of several CICS systems. Each time, multiple examples of an exchange will operate concurrently in a CICS structure. A solitary case of a running exchange is known as an assignment.

It has elite use of (or keeps a lock for) any data commodity it modifies during the time that an assignment is running, preserving the exchange’s separation rights. Once the lock is delivered, various undertakings that expect access to the properties must stand by. To ensure the exchange handling system is generally sensitive, you schedule the CICS implementation programs so that they keep locks for the shortest possible time. For instance, you can plan your exchanges to be fleeting in light of the fact that CICS discharges locks when an errand closes.

Benefits of ACID Transactions

Absolute Data Integrity and Safety:

Maintaining a strategic distance from lost updates, filthy peruses, flat peruses, and authorising application explicit respectability requirements are basic worries for application engineers. This is particularly evident when building clients confronting applications in verticals, for example, budgetary administrations, retail, and SaaS. Settling these worries legitimately at the information base layer utilising the consistency given by ACID exchanges is a lot less complex methodology.

ACID Image 2

Simplified Concurrency Control:

Simultaneous admittance to shared assets, for example, retail stock, bank parity, and gaming leaderboards is unavoidable. Confinement in ACID exchanges act the hero of application engineers. For example, at the point when an information base ensures exchanges with serialisable segregation, engineers can regard every exchange as though it were executed successively, despite the fact that it might really be executed simultaneously. Grave thinking about likely clashes between tasks from isolated exchanges is blocked through and through.

ACID Image 3

Intuitive Data Access Logic:

Corrosive agreeable information bases ordinarily permit complex pattern demonstrating and local help for multi-step information control tasks, for example, reliable auxiliary lists. Business rationale can be presently spoken to all the more legitimately in the application code.

ACID Image 4

Future-Proofing Database Needs:

Strength is once in a while disputable in information bases where stable tirelessness is an absolute necessity. Henceforth our view is that “in-memory” just frameworks ought not be even viewed as information bases! In any case, there is consistently a desire on some portion of engineers to compromise either Atomicity or Consistency or Isolation or a blend of them as an end-result of better in conveyed information bases. While these trade-offs are at times simpler to legitimise in the short run, the loss of adaptability over the long haul accompanies a weighty expense. Upper hand in business originates from the capacity to upgrade applications quickly. For example, an inside, dashboards-just, non-value-based application can be changed into a client confronting value-based application in insignificant time if and just if the first information base was future-verification for such a change.

ACID Image 5

What’s Needed for Implementing ACID?

For any solid or disseminated information base to execute ACID exchanges, there are four central perspectives that should be planned and created.

Provisional Updates (Atomicity):

Exchanges include numerous tasks over various lines. Given the need to regard every one of these activities as a solitary unit, some type of temporary update in a brief space is required previously followed by a submit.

 Strongly Consistent Core (Consistency):

An emphatically predictable center is the reason for accomplishing ACID assurances in an exchange including just a solitary procedure on a solitary line. The extra information trustworthiness imperatives expected to accomplish full ACID (with numerous activities over different columns) are based on the head of this center.

Transaction Ordering (Isolation):

For an information base to help the draconian serialisable confinement level, a system, for example, worldwide arranged timestamps is expected to consecutively organise all the exchanges. Then again, the depiction separation level depends on an incomplete request where sub-activities in a single exchange may interleave with those from different exchanges. The advantage is lower inertness and higher all through than serialisable level while proceeding to distinguish compose clashes.

Persistent Storage (Durability):

Contrasted with the other three properties, toughness is the most straightforward to accomplish by just utilising a capacity motor that can store information in a hidden persevering gadget, for example, HDDs and SSDs. Our post A Busy Developer’s Guide to Database Storage Engines clarifies how different kinds of capacity motors work and the particular remaining burden designs they are typically enhanced for.

Why ACID Became Optional?

Corrosive consistency was underestimated in solid information bases of the past. This is on the grounds that the solid information base worker can make temporary updates, is unequivocally reliable of course, runs on tireless circles, and above all can go about as a solitary wellspring of truth for the requesting of simultaneous exchanges.

As information bases got appropriated and NoSQL began late 2000s, the primary thing to get done was to choose the adherence to the CAP Theorem. The default decision was Availability over Consistency given the attention on large information outstanding tasks at hand that don’t need outright accuracy. Net outcome was that the establishment essential for the Consistency in ACID was undermined. It got simpler to abandon Atomicity and Isolation from that point. Every hub accompanied its own information base worker that had command over its own subset of information in the general bunch. Making temporary updates over different such hubs and doing as such with some requesting was considered intricate and superfluous. Simultaneously, conditional information volumes were sufficiently low and could be fulfilled by vertical scaling of solid ACID consistent information bases. The absence of ACID in dispersed information bases didn’t hurt customary endeavours as of not long ago.


Corrosive exchanges are a key component of operational information bases. They help endeavours at the same time gain client information trustworthiness and application improvement readiness. Executing ACID exchanges in an information base requires critical frameworks designing exertion, particularly when the data set is appropriated over numerous hubs. In this subsequent post on disseminated ACID exchanges with the elite, we jump further into the difficulties in question and perceive how cutting edge circulated information bases, for example, YugabyteDB are comprehending those difficulties. Then, you can see YugabyteDB’s disseminated exchanges in real life utilising a nearby bunch.


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  4. Frank, L., & Pedersen, R. U. (2014, January). Managing consistency anomalies in distributed integrated databases with relaxed ACID properties. In Proceedings of the 8th International Conference on Ubiquitous Information Management and Communication (pp. 1-7).