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CAP Theorem
In theoretical computer science, the CAP theorem, also named Brewer's theorem after computer scientist Eric Brewer, states that any distributed data store can provide only two of the following three guarantees:Seth Gilbert and Nancy Lynch"Brewer's conjecture and the feasibility of consistent, available, partition-tolerant web services" ''ACM SIGACT News'', Volume 33 Issue 2 (2002), pg. 51–59. . ; Consistency: Every read receives the most recent write or an error. ; Availability: Every request receives a (non-error) response, without the guarantee that it contains the most recent write. ; Partition tolerance: The system continues to operate despite an arbitrary number of messages being dropped (or delayed) by the network between nodes. When a network partition failure happens, it must be decided whether to do one of the following: * cancel the operation and thus decrease the availability but ensure consistency * proceed with the operation and thus provide availability but risk i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theoretical Computer Science
Theoretical computer science (TCS) is a subset of general computer science and mathematics that focuses on mathematical aspects of computer science such as the theory of computation, lambda calculus, and type theory. It is difficult to circumscribe the theoretical areas precisely. The Association for Computing Machinery, ACM's ACM SIGACT, Special Interest Group on Algorithms and Computation Theory (SIGACT) provides the following description: History While logical inference and mathematical proof had existed previously, in 1931 Kurt Gödel proved with his incompleteness theorem that there are fundamental limitations on what statements could be proved or disproved. Information theory was added to the field with a 1948 mathematical theory of communication by Claude Shannon. In the same decade, Donald Hebb introduced a mathematical model of Hebbian learning, learning in the brain. With mounting biological data supporting this hypothesis with some modification, the fields of n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NoSQL
A NoSQL (originally referring to "non- SQL" or "non-relational") database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relational databases. Such databases have existed since the late 1960s, but the name "NoSQL" was only coined in the early 21st century, triggered by the needs of Web 2.0 companies. NoSQL databases are increasingly used in big data and real-time web applications. NoSQL systems are also sometimes called Not only SQL to emphasize that they may support SQL-like query languages or sit alongside SQL databases in polyglot-persistent architectures. Motivations for this approach include simplicity of design, simpler "horizontal" scaling to clusters of machines (which is a problem for relational databases), finer control over availability and limiting the object-relational impedance mismatch. The data structures used by NoSQL databases (e.g. key–value pair, wide column, graph, or document ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zooko's Triangle
Zooko's triangle is a trilemma of three properties that some people consider desirable for names of participants in a network protocol: * ''Human-meaningful:'' Meaningful and memorable (low-entropy) names are provided to the users. * ''Secure:'' The amount of damage a malicious entity can inflict on the system should be as low as possible. * ''Decentralized:'' Names correctly resolve to their respective entities without the use of a central authority or service. Overview Zooko Wilcox-O'Hearn conjectured that no single kind of name can achieve more than two. For example: DNSSec offers a human-meaningful, secure naming scheme, but is not decentralized as it relies on trusted root-servers; .onion addresses and bitcoin addresses are secure and decentralized but not human-meaningful; and I2P uses name translation services which are secure (as they run locally) and provide human-meaningful names - but fail to provide unique entities when used globally in a decentralised network withou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Raft (computer Science)
A raft is any flat structure for support or transportation over water. It is usually of basic design, characterized by the absence of a hull. Rafts are usually kept afloat by using any combination of buoyant materials such as wood, sealed barrels, or inflated air chambers (such as pontoons), and are typically not propelled by an engine. Rafts are an ancient mode of transport; naturally-occurring rafts such as entwined vegetation and pieces of wood have been used to traverse water since the dawn of humanity. Human-made rafts Traditional or primitive rafts were constructed of wood or reeds. Modern rafts may also use pontoons, drums, or extruded polystyrene blocks. Inflatable rafts up to the 20th century used flotation chambers made of goat- or buffalo-skins, but most now use durable, multi-layered rubberized fabrics. Depending on its use and size, it may have a superstructure, masts, or rudders. Timber rafting is used by the logging industry for the transportation of logs, b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paxos (computer Science)
Paxos is a family of protocols for solving consensus in a network of unreliable or fallible processors. Consensus is the process of agreeing on one result among a group of participants. This problem becomes difficult when the participants or their communications may experience failures. Consensus protocols are the basis for the state machine replication approach to distributed computing, as suggested by Leslie Lamport and surveyed by Fred Schneider. State machine replication is a technique for converting an algorithm into a fault-tolerant, distributed implementation. Ad-hoc techniques may leave important cases of failures unresolved. The principled approach proposed by Lamport et al. ensures all cases are handled safely. The Paxos protocol was first submitted in 1989 and named after a fictional legislative consensus system used on the Paxos island in Greece, where Lamport wrote that the parliament had to function "even though legislators continually wandered in and out of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fallacies Of Distributed Computing
The fallacies of distributed computing are a set of assertions made by L Peter Deutsch and others at Sun Microsystems describing false assumptions that programmers new to distributed applications invariably make. The fallacies The fallacies are # The network is reliable; # Latency is zero; # Bandwidth is infinite; # The network is secure; # Topology doesn't change; # There is one administrator; # Transport cost is zero; # The network is homogeneous. The effects of the fallacies # Software applications are written with little error-handling on networking errors. During a network outage, such applications may stall or infinitely wait for an answer packet, permanently consuming memory or other resources. When the failed network becomes available, those applications may also fail to retry any stalled operations or require a (manual) restart. # Ignorance of network latency, and of the packet loss it can cause, induces application- and transport-layer developers to allow unbounded t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Blockchain
A blockchain is a type of distributed ledger technology (DLT) that consists of growing lists of records, called ''blocks'', that are securely linked together using cryptography. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data (generally represented as a Merkle tree, where data nodes are represented by leaves). The timestamp proves that the transaction data existed when the block was created. Since each block contains information about the previous block, they effectively form a ''chain'' (compare linked list data structure), with each additional block linking to the ones before it. Consequently, blockchain transactions are irreversible in that, once they are recorded, the data in any given block cannot be altered retroactively without altering all subsequent blocks. Blockchains are typically managed by a peer-to-peer, peer-to-peer (P2P) computer network for use as a public distributed ledger, where nodes collectively adhere to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PACELC Theorem
In theoretical computer science, the PACELC theorem is an extension to the CAP theorem. It states that in case of network partitioning (P) in a distributed computer system, one has to choose between availability (A) and consistency (C) (as per the CAP theorem), but else (E), even when the system is running normally in the absence of partitions, one has to choose between latency (L) and consistency (C). Overview PACELC builds on the CAP theorem. Both theorems describe how distributed databases have limitations and tradeoffs regarding consistency, availability, and partition tolerance. PACELC however goes further and states that an additional trade-off exists: between latency and consistency, even in absence of partitions, thus providing a more complete portrayal of the potential consistency trade-offs for distributed systems. A high availability requirement implies that the system must replicate data. As soon as a distributed system replicates data, a trade-off between consisten ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theorem
In mathematics, a theorem is a statement that has been proved, or can be proved. The ''proof'' of a theorem is a logical argument that uses the inference rules of a deductive system to establish that the theorem is a logical consequence of the axioms and previously proved theorems. In the mainstream of mathematics, the axioms and the inference rules are commonly left implicit, and, in this case, they are almost always those of Zermelo–Fraenkel set theory with the axiom of choice, or of a less powerful theory, such as Peano arithmetic. A notable exception is Wiles's proof of Fermat's Last Theorem, which involves the Grothendieck universes whose existence requires the addition of a new axiom to the set theory. Generally, an assertion that is explicitly called a theorem is a proved result that is not an immediate consequence of other known theorems. Moreover, many authors qualify as ''theorems'' only the most important results, and use the terms ''lemma'', ''proposition'' and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nancy Lynch
Nancy Ann Lynch (born January 19, 1948) is a mathematician, a theorist, and a professor at the Massachusetts Institute of Technology. She is the NEC Professor of Software Science and Engineering in the EECS department and heads the "Theory of Distributed Systems" research group at MIT's Computer Science and Artificial Intelligence Laboratory. Education and early life Lynch was born in Brooklyn, and her academic training was in mathematics. She attended Brooklyn College and MIT, where she received her Ph.D. in 1972 under the supervision of Albert R. Meyer. Work She served on the math and computer science faculty at several other universities, including Tufts University, the University of Southern California, Florida International University, and the Georgia Institute of Technology (Georgia Tech), prior to joining the MIT faculty in 1982. Since then, she has been working on applying mathematics to the tasks of understanding and constructing complex distributed systems. Her 1985 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Seth Gilbert
Seth,; el, Σήθ ''Sḗth''; ; "placed", "appointed") in Judaism, Christianity, Islam, Mandaeism, and Sethianism, was the third son of Adam and Eve and brother of Cain and Abel, their only other child mentioned by name in the Hebrew Bible. According to , Seth was born after Abel's murder by Cain, and Eve believed that God had appointed him as a replacement for Abel. Genesis According to the Book of Genesis, Seth was born when Adam was 130 years old (according to the Masoretic Text), or 230 years old (according to the Septuagint), "a son in his likeness and image". The genealogy is repeated at . states that Adam fathered "sons and daughters" before his death, aged 930 years. According to Genesis, Seth died at the age of 912 (that is, 14 years before Noah's birth). (2962 BC) Jewish tradition Seth figures in the pseudepigraphical texts of the ''Life of Adam and Eve'' (the ''Apocalypse of Moses''). It recounts the lives of Adam and Eve from after their expulsion from the Garden ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Symposium On Principles Of Distributed Computing
The Symposium on Principles of Distributed Computing (PODC) is an academic conference in the field of distributed computing organised annually by the Association for Computing Machinery (special interest groups SIGACT and SIGOPS). Scope and related conferences Work presented at PODC typically studies theoretical aspects of distributed computing, such as the design and analysis of distributed algorithms. The scope of PODC is similar to the scope of International Symposium on Distributed Computing (DISC), with the main difference being geographical: DISC is usually organized in European locations,DISC in . while PODC has been traditionally held in North America. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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