Letteratura scientifica selezionata sul tema "Leaderless SMR"

Introduction The Disney brand has become synonymous with magic through its numerous depictions of spells, curses, prophecies, and pixie dust. Thus, it is ironic that in 2023, the 100th anniversary of the Walt Disney Studio’s founding (“Disney History”), the final film released during Walt Disney’s life, The Sword in the Stone (celebrating its 60th anniversary) remains stuck in obscurity (Aronstein 129) despite being steeped in magic and wizardry. The Sword in the Stone is regarded as “one of the most obscure [films] in the Disney animated canon” (Booker 38). Although it performed moderately well during its debut in 1963, its 1983 re-release and home video sales failed to renew public interest. To date, The Sword in the Stone has no games, comic series, or even Disneyland merchandise (Aronstein 129). The film is hardly a technical marvel; its sketchy animation style and blue-slate backgrounds create a dingy, unfinished look (Beck 272), while its simplistic storyline and anachronistic humour have been criticised for being ill-matched with its Arthurian subject matter (Gossedge 115). Despite these flaws, The Sword in the Stone offers the studio’s most fully rendered representation of Disney magic as benevolent forces sourced in learning and discipline that enable good-hearted protagonists to prepare for future leadership roles. By approaching the film as a didactic text separate from its Arthurian origins, I will demonstrate how The Sword in the Stone defines magic, not by nebulous spells or hexes, but by its facilitation of societal advancement and transformative powers via the educated mind. Young Arthur’s Humble Beginnings Based loosely on T.H. White’s 1938 novel of the same name (Valle 224), The Sword in the Stone takes place in medieval Europe, with most of its action occurring in a rotting castle and surrounding wolf-infested forests. In this threatening world, magic takes many forms, from powerful acts of “sorcery” to comical displays of “Latin business”. The first allusion to magic occurs during the film’s opening song, which establishes its setting (“when England was young”) and primary conflict (“the good king had died, and no one could decide who was rightful heir”). Without a ruler, England will be destroyed by civil war unless miraculous forces intervene on its behalf. This ‘miracle’ is the eponymous sword in the stone that the rightful ruler of England will free. The sword is destined for King Arthur, but as he is only an orphaned child living in obscurity at the film’s beginning, no one manages to retrieve the sword in his stead, and so the ‘miracle’ seemingly fails. The film’s off-screen narrator describes this leaderless period as “a dark age … where the strong preyed upon the weak”. As a force that trumps brute strength, magic is prized by those who can wield it, particularly the wizard Merlin. Magic is regarded with suspicion by the majority who cannot practice it (Valle 234), though they still recognise its legitimacy. Even Arthur’s practical stepfather, Sir Ector, begs Merlin not to practice any “black magic” on his family after Merlin creates an indoor “wizard blizzard” to prove his seriousness in tutoring Arthur. Merlin is a far cry from the mysterious soothsayer of Arthurian legend. He has been Disneyfied into a caricature of the famed wizard, appearing more like an eccentric academic than an all-seeing mystic (Beck 272). Susan Aronstein describes him as “the reification of Disney’s post-World War II rebranding of itself as a leader in education in the wake of a postwar shift in American child rearing” (130)—a playful pedagogue who makes learning fun for Arthur and audiences. After meeting Arthur in the woods near his home, Merlin becomes determined to rectify the boy’s educational deficiencies. It is not yet clear whether Merlin knows who Arthur is or will become; Merlin merely repeats to his owl companion, Archimedes, that the boy needs an education—specifically, a modern education. In addition to presenting Arthur with evidence of his travels to the future, such as helicopter models, Merlin rattles off a litany of subjects common to twentieth-century American curricula (English, science, mathematics) but hardly the sort of fare pages of Arthur’s status would study in fifth-century England. Because Arthur’s royal lineage is unknown to him, he aspires to be a squire for his soon-to-be-knighted stepbrother and so must learn the rules of jousting and horsemanship when not otherwise preoccupied with page duties. These include scrubbing pots and pans, cleaning floors, and fetching anything his stepfather requests. While Arthur is not resistant to Merlin’s attempts to teach him, he struggles to balance Merlin’s demands on his time with Sir Ector’s (Pinsky 85). Young Arthur’s gangly stature conveys how stretched the boy is between his indentured servitude to Ector and Merlin’s insistence upon his liberation through education. Arthur is constantly in motion, scurrying from one task to the next to please all parties involved and often failing to do so. Each time Merlin’s instruction causes the boy to miss Sir Ector’s call, Arthur is punished with additional duties (Holcomb et al.). Merlin’s Instructive Magic Merlin uses magic to bridge the gap between Arthur’s responsibilities to his present and his future. The word “magic” is spoken fifteen times in the film, six by Merlin himself. The wizard first utters the word after packing his entire house (furniture and all) into a carpet bag. Arthur is impressed, but Merlin warns him that magic is no panacea: “don’t you get any foolish ideas that magic will solve all your problems”. Even Merlin struggles to convince Sir Ector to let him tutor Arthur and to prevent predatory animals from killing the boy during their adventures together. Magic has limits. It cannot penetrate the minds of humans nor quell the instincts of wild animals. Its impact seems restricted to the physical world. Merlin primarily uses magic for physical transformation; his lessons centre on changing Arthur into different animals to enable the future king to experience life from others’ perspectives. Merlin turns Arthur into a fish, a squirrel, and a bird, with each animal’s situation representing increasingly complex problems that Arthur must overcome. Each lesson also corresponds with one or more levels of Maslow’s hierarchy of needs: (1) safety and survival, (2) love and belonging, and (3) self-esteem and self-actualisation (Lester 15). As a perch swimming around the castle moat, Arthur learns to use his intellect to evade a toothy pike that nearly eats him alive. As a squirrel, Arthur observes the heartbreak of unrequited love, foreshadowing his complicated love triangle with Guinevere and Lancelot (Grellner 125). In avian form, Arthur experiences a much-needed boost in his self-worth after Sir Ector strips him of his squire-in-training status. In flight, Arthur seems most in his element. After struggling with the logistics of swimming as a fish and navigating trees as a squirrel, Arthur soars over the countryside, even showing off his acrobatics to Archimedes flying alongside him. Although Arthur relishes these experiences, he does not seem to grasp their broader implications. He describes his first magical lesson as “so much fun” (despite having nearly died) and pauses only momentarily at the end of his second lesson to reflect on the emotional damage he causes a heartbroken female squirrel who falls madly in love with him. Still, Arthur faces mortal danger with each lesson, so one could argue that by transforming the young boy into different animals, Merlin is honing Arthur’s problem-solving skills (Holcomb et al.). Madam Mim’s Destructive Magic When Arthur is turned into a bird, his third lesson takes an unexpected turn. After narrowly escaping a hawk, Arthur flies into the forest and falls down the chimney of a rival magician named Mad Madam Mim. After introducing herself, Mim insists to Arthur that she has far more magic “in one little finger” than Merlin possesses in his entire repertoire. She displays her powers by killing plants, changing sizes, and making herself monstrous or lovely according to her whims. Mim’s demonstrations suggest a breezy familiarity with magic that Merlin lacks. Whereas Merlin sometimes forgets the “Latin business” needed to invoke spells, Mim effortlessly transitions from one transformation to another without any spell use. The source of her power soon becomes apparent. “Black sorcery is my dish of tea”, she croons to Arthur. Compared to Merlin’s Latin-based magic, Mim’s “black sorcery” is easier to master and well-suited to her undisciplined lifestyle. Mim’s cottage is filthy and in disrepair, yet she is playing solitaire (and cheating) when Arthur stumbles into her fireplace. This anachronism (since playing cards would not be introduced to Europeans until the fourteenth century; DeBold) characterises, through visual shorthand, Mim’s idle hands as the Devil’s workshop; she also possesses a modern dartboard that she throws Arthur against. Unlike Merlin’s domicile, Mim’s cottage contains no books, scientific instruments, or other props of study, indicating that there is no deeper understanding behind her magic. As Latin is the root language of science and law, it seems fitting that Latin is not part of Mim’s repertoire. She simply points a finger at an unfortunate subject, and it bends to her will—or dies. Efficient though Mim’s magic may be, its power is fleeting. Mim briefly changes herself into a beautiful young woman. But she concedes that her magic is “only skin deep” and turns herself back into “an ugly old creep”. Evidently, her magic’s potency does not last long, nor is it capable of improving her situation, as she continues living in her broken-down cottage as a bored, friendless hermit. Her black magic may be easy to master but cannot impart meaningful change. And so, while Merlin can use his magic to improve Arthur’s life, Mim’s magic can only serve the status quo described at the film’s beginning: the strong preying upon the weak. Although Mim lives outside the feudal social hierarchy, she uses her magic to terrorise any unfortunate creatures who wander into her clutches, including Arthur. When Arthur (still in bird form) states that he prefers the benevolence and usefulness of Merlin’s magic, an infuriated Mim transforms herself into a hungry cat and chases Arthur around the cottage until Merlin arrives to save the boy. Merlin then challenges Mim to a wizard’s duel, during which he and Mim attack each other in animal forms ranging from foxes and caterpillars to tigers, goats, and elephants. Each time Mim transforms, she does so seamlessly, requiring no momentary pause to recall a spell, unlike Merlin, who stumbles across the Latin phrases necessary to change himself into something faster or bigger. But after Merlin transforms into a walrus and squashes a clucking chicken Mim, the momentum shifts in his favour. Her magic becomes tinged with rage that causes her to make mistakes, including biting herself as a snake and ramming herself into a tree in rhinoceros form. Merlin’s disciplined playing style is nearly errorless. Although he becomes frightened when Mim transforms into a fire-breathing dragon, Merlin continues to play sensibly and courageously. His final winning move is to transform himself into a measle-like germ that incapacitates Mim with violent sneezing and cold flashes (Perciaccante and Coralli 1171). Arthur is astonished by the brilliant manoeuvring of his mentor, who manages to win the duel fairly “by dint of his knowledge and study” (Pinsky 86). After stating the lesson’s summative point for Merlin—“knowledge and wisdom is the real power”—Arthur vows to redouble his efforts to complete his education. Education: The Film’s Real Magic The lesson for viewers is simple enough: an education has a magical impact on one’s life. Put more succinctly, education is magic. Merlin defeats Mim because of his greater knowledge and cleverer use of spells. Arthur will overcome his low social status and ascend to the throne by becoming literate and sharpening his intellect. But as with Merlin’s acquisition of magical knowledge through intense study, Arthur’s royal ascension must be earned. He must learn the literal ABCs of language acquisition to gain others’ shared knowledge, as illustrated by a scene in which Archimedes painstakingly teaches Arthur how to write the alphabet in preparation for reading an enormous stack of books. Merlin cannot magically impart such knowledge to the future king; Arthur must learn it through sustained effort. He also must learn to make informed decisions rather than respond to panic or anger as Mim does during her duel with Merlin. Herein lies the distinction between Mim’s and Merlin’s magic: transformative impact. Mim’s black magic has locked her into her chosen fate. By using her powers to amuse herself or cause others harm, Mim perpetuates her outcast status as the stereotypical witch to be feared (Valle 234). While her cottage contains anachronistic elements such as playing cards (suggesting that she, like Merlin, has time-travelled), it contains no evidence of the modern advances that Merlin shares with Arthur, like aeroplane models, nor anything that might improve their feudal society. Merlin’s magic, by contrast, facilitates immediate changes to Arthur’s world and offers the promise of technological advancements in the centuries to come. To reduce the boy’s workload, for instance, Merlin magically conjures up a factory-style assembly line of brushes, tubs, and mops to wash dishes and scrub kitchen floors. Merlin also shares his knowledge of humankind’s future achievements with Arthur to advance his education, providing him with models, maps, globes, and hundreds of books. To become a proper king, Arthur must learn how to use such information to others’ advantage, not just his own. As Caroline Buts and Jose Luis Buendia Sierra observe of magic’s paradox, “using the wand without knowing properly the rules may sometimes lead to catastrophic situations” (509). This point is reaffirmed in the film’s final sequence, which takes place in London on New Year’s Day at a jousting tournament, the winner of which will be crowned king of England. Arthur, now a squire to his recently knighted stepbrother, forgets to bring his stepbrother’s sword to the tournament grounds. He attempts to replace the missing weapon with the sword in the stone when he spots the aging relic in a nearby churchyard. As Arthur pulls out the sword, angelic choral music swells, signalling that the rightful ruler of England has fulfilled the prophecy. After some scepticism from the assembled masses, Sir Ector and the other knights and spectators bow to the befuddled twelve-year-old. The film’s final scene shows a panic-stricken Arthur conceding that he does not know how to rule England and crying out for Merlin. When the wizard blows in from his most recent trip to the twentieth century, he confirms that he has known all along who Arthur is and assures the boy that he will become a great king. Arthur seems ready to put in the work, recognising that his knowledge and wisdom will improve the lives of England’s inhabitants. Conclusion Magic is thus portrayed as an intervening force that either facilitates or stymies societal progress. Good magic ensures that intelligent, educated individuals such as Arthur become great leaders, while those who would attain positions of power through brute force are thwarted from doing so. At the film’s conclusion, Arthur has not been fully transformed into a great leader because his education is far from finished; he has only learned enough to realise that he knows too little to rule effectively. Yet, from the Socratic perspective, such self-awareness is the germination for attaining true wisdom (Tarrant 263). Arthur also already knows that he will not be able to learn how to rule well through trickery or shortcuts, even with a powerful magician by his side. But the film’s closing scene reiterates this point with Merlin promising Arthur that he will succeed. “Why, they might even make a motion picture about you!” he exclaims in a clever fourth-wall joke (Gellner 120). The Sword in the Stone’s mere existence proves that Arthur will acquire the knowledge and wisdom necessary to become a truly great monarch. The fledgling pupil will live long and rule well, not because of pixie dust or magic spells, but because of his willingness to learn and to be transformed by his education into a wise and fair ruler. References Aronstein, Susan. “‘Higitus Figitus!’ Of Merlin and Disney Magic.” It’s the Disney Version! Popular Cinema and Literary Classics. Eds. Douglas Brode and Shea T. Brode. Lanham, MD: Rowman & Littlefield. 129-139. Beck, Jerry. The Animated Movie Guide. Chicago: A Capella, 2005. Booker, M. Keith. Disney, Pixar, and the Hidden Messages of Children's Films. Santa Barbara: ABC-CLIO, 2010. Buts, Caroline, and Jose Luis Buendia Sierra. “The Sword in the Stone.” European State Aid Law Quarterly 16.4 (2017): 509-511. 10 June 2023 <https://www.jstor.org/stable/10.2307/26694185>. DeBold, Elizabeth. “Fortune’s Fools: Early Tarot Cards.” The Collation: Folger Shakespeare Library 2 Feb. 2021. 5 June 2023 <https://www.folger.edu/blogs/collation/fortunes-fools-early-tarot-cards/>. “Disney History.” D23, 2023. <https://d23.com/disney-history/>. Gossedge, Rob. “The Sword in the Stone: American Translatio and Disney’s Antimedievalism.” The Disney Middle Ages: A Fairy-Tale and Fantasy Past. Eds. Tison Pugh and Susan Aronstein. Palgrave Macmillan: 2012. 115–131. Grellner, Alice. “Two Films That Sparkle: The Sword in the Stone and Camelot.” Cinema Arthuriana: Twenty Essays. Rev. ed. Ed. Kevin J. Harty. Jefferson, NC: McFarland, 2010. 118-126. Holcomb, Jeanne, Kenzie Latham, and Daniel Fernandez-Baca. “Who Cares for the Kids? Caregiving and Parenting in Disney Films.” Journal of Family Issues 36.14 (2015): 1957–81. DOI: 10.1177/0192513X13511250. Lester, David. “Measuring Maslow’s Hierarchy of Needs.” Psychological Reports: Mental & Physical Health 113.1 (2013): 15-17. 20 May 2023 <https://doi.org/10.2466/02.20.PR0.113x16z1>. Perciaccante, Antonio, and Alessia Coralli. “The Virus Defeating Madam Mim.” American Journal of Infection Control 45.10 (2017): 1171. 1 June 2023 <http://doi.org/10.1016/j.ajic.2017.07.017>. Pinsky, Mark I. The Gospel According to Disney: Faith, Trust, and Pixie Dust. Louisville, KY: Westminster John Knox Press, 2004. The Sword in the Stone. Dir. Wolfgang Reitherman. Perf. Karl Swenson and Rickie Sorensen. Buena Vista, 1963. Tarrant, Harold. “Socratic Method and Socratic Truth.” A Companion to Socrates. Eds. Sara Ahbel-Rappe and Rachana Kamtekar. Malden, MA: Blackwell, 2006. 254-272. Valle, Maria Luiza Cyrino. "The New Matter of Britain: T.H. White's The Sword in the Stone." Estudos Germânicos 5.1 (1984): 224-265.

Les services distribués modernes doivent être hautement disponibles, car nos sociétés en sont de plus en plus dépendantes. La manière la plus courante d'obtenir une haute disponibilité est de répliquer les données dans plusieurs répliques du service. De cette façon, le service reste opérationnel en cas de pannes, car les clients peuvent être relayés vers d'autres répliques qui fonctionnent. Dans les systèmes distribués, la technique classique pour mettre en œuvre de tels services tolérants aux pannes est appelée réplication de machine d'état (State-Machine Replication, SMR), où un service est défini comme une machine d'état déterministe et chaque réplique conserve une copie locale de la machine. Pour garantir la cohérence du service, les répliques se coordonnent entre elles et conviennent de l'ordre des transitions à appliquer à leurs copies de la machine d'état. La réplication effectuée par les services Internet modernes s'étend sur plusieurs lieux géographiques (géo-réplication). Cela permet une disponibilité accrue et une faible latencea, puisque les clients peuvent communiquer avec la réplique géographique la plus proche. En raison de leur dépendance avec une réplique leader, coordonnant les changements de transition, les protocoles SMR classiques offrent une évolutivité et une disponibilité limitées dans ce contexte. Pour résoudre ce problème, les protocoles récents suivent plutôt une approche sans leader, dans laquelle chaque réplique est capable de progresser en utilisant un quorum de ses pairs. Ces nouveaux protocoles sans leader sont complexes et chacun d'entre eux présente une approche ad-hoc de l'absence de leader. La première contribution de cette thèse est un framework qui capture l'essence de SMR sans leader (Leaderless SMR) et la formalisation de certaines de ses limites. En raison de la nature de plus en plus sensible des services répliqués, l'utilisation de simples pannes bénignes n'est plus suffisante. Les recherches récentes se dirigent vers le développement de protocoles qui supportent le comportement arbitraire de certaines répliques (pannes Byzantines) et qui prospèrent également dans un environnement géo-répliqué. Les blockchains sont un exemple de ce nouveau type de services répliqués sensibles qui a fait l'objet de nombreuses recherches. Les blockchains sont alimentées par des protocoles de réplication byzantins adaptés pour fonctionner sur des centaines, voire des milliers de répliques. Lorsque le contrôle de membership à ces répliques est ouvert, c'est-à-dire que n'importe qui peut faire fonctionner une réplique, on dit que la blockchain est permissionless. Dans le cas inverse, lorsque l'adhésion est contrôlée par un ensemble d'entités connues, comme des entreprises, nous disons que la blockchain est permissioned. Les blockchains permissioned utilisent des protocoles SMR byzantins. Comme ces protocoles utilisent un leader, ils souffrent de problèmes d'évolutivité et de disponibilité, de la même manière que leurs homologues non byzantins. Dans la deuxième partie de cette thèse, nous adaptons notre framework pour supporter les pannes byzantines et présentons le premier framework pour le SMR byzantin sans leader. De plus, nous montrons que lorsqu'il est correctement instancié, il permet de contourner les problèmes de scalabilité dans les protocoles SMR byzantins dirigés par des leaders pour les permissioned blockchains
Modern distributed services are expected to be highly available, as our societies have been growing increasingly dependent on them. The common way to achieve high availability is through the replication of data in multiple service replicas. In this way, the service remains operational in case of failures as clients can be relayed to other working replicas. In distributed systems, the classic technique to implement such fault-tolerant services is called State-Machine Replication (SMR), where a service is defined as a deterministic state-machine and each replica keeps a local copy of the machine. To guarantee that the service remains consistent, replicas coordinate with each other and agree on the order of transitions to be applied to their copies of the state-machine. The replication performed by modern Internet services spans across several geographical locations (geo-replication). This allows for increased availability and low latency, since clients can communicate with the closest geo-graphical replica. Due to their reliance on a leader replica, classical SMR protocols offer limited scalability and availability under this setting. To solve this problem, recent protocols follow instead a leaderless approach, in which each replica is able to make progress using a quorum of its peers. These new leaderless protocols are complex and each one presents an ad-hoc approach to leaderlessness. The first contribution of this thesis is a framework that captures the essence of Leaderless State-Machine Replication (Leaderless SMR) and the formalization of some of its limits. Due to the increasingly sensitive nature of replicated services, leveraging simple benign failures is no longer enough. Recent research is headed towards developing protocols that support arbitrary behavior of some replicas (Byzantine failures) and that also thrive in a geo-replicated environment. An example of this new type of sensitive replicated services that has been the focus of a lot of research are blockchains. Blockchains are powered by Byzantine replication protocols adapted to work over hundreds or even thousands of replicas. When the membership control over such replicas is open, that is, anyone can run a replica, we say the blockchain is permissionless. In the converse case, when the membership is controlled by a set of known entities like companies, we say the blockchain is permissioned. When such Byzantine protocols follow the classic leader-driven approach they suffer from scalability and availability issues, similarly to their non-byzantine counterparts. In the second part of this thesis, we adapt our framework to support Byzantine failures and present the first framework for Byzantine Leaderless SMR. Furthermore, we show that when properly instantiated it allows to sidestep the scalability problems in leader-driven Byzantine SMR protocols for permissioned blockchains