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Two-phase Commit Protocol
In transaction processing, databases, and computer networking, the two-phase commit protocol (2PC) is a type of atomic commitment protocol (ACP). It is a distributed algorithm that coordinates all the processes that participate in a distributed atomic transaction on whether to commit or abort (roll back) the transaction. This protocol (a specialised type of consensus protocol) achieves its goal even in many cases of temporary system failure (involving either process, network node, communication, etc. failures), and is thus widely used. Philip A. Bernstein, Vassos Hadzilacos, Nathan Goodman (1987) ''Concurrency Control and Recovery in Database Systems'' Chapter 7, Addison Wesley Publishing Company, Gerhard Weikum, Gottfried Vossen (2001) ''Transactional Information Systems'' Chapter 19, Elsevier, Philip A. Bernstein, Eric Newcomer (2009)''Principles of Transaction Processing'', 2nd Edition, Chapter 8, Morgan Kaufmann (Elsevier), However, it is not resilient to all possible fail ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transaction Processing
Transaction processing is information processing in computer science that is divided into individual, indivisible operations called ''transactions''. Each transaction must succeed or fail as a complete unit; it can never be only partially complete. For example, when you purchase a book from an online bookstore, you exchange money (in the form of credit) for a book. If your credit is good, a series of related operations ensures that you get the book and the bookstore gets your money. However, if a single operation in the series fails during the exchange, the entire exchange fails. You do not get the book and the bookstore does not get your money. The technology responsible for making the exchange balanced and predictable is called transaction processing. Transactions ensure that data-oriented resources are not permanently updated unless all operations within the transactional unit complete successfully. By combining a set of related operations into a unit that either completely s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Write Ahead Logging
In computer science, write-ahead logging (WAL) is a family of techniques for providing atomicity and durability (two of the ACID properties) in database systems. A write ahead log is an append-only auxiliary disk-resident structure used for crash and transaction recovery. The changes are first recorded in the log, which must be written to stable storage, before the changes are written to the database. The main functionality of a write-ahead log can be summarized as: * Allow the page cache to buffer updates to disk-resident pages while ensuring durability semantics in the larger context of a database system. * Persist all operations on disk until the cached copies of pages affected by these operations are synchronized on disk. Every operation that modifies the database state has to be logged on disk before the contents on the associated pages can be modified * Allow lost in-memory changes to be reconstructed from the operation log in case of a crash. In a system using WAL, al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Two Generals' Problem
In computing, the Two Generals' Problem is a thought experiment meant to illustrate the pitfalls and design challenges of attempting to coordinate an action by communicating over an unreliable link. In the experiment, two generals are only able to communicate with one another by sending a messenger through enemy territory. The experiment asks how they might reach an agreement on the time to launch an attack, while knowing that any messenger they send could be captured. The Two Generals' Problem appears often as an introduction to the more general Byzantine Generals problem in introductory classes about computer networking (particularly with regard to the Transmission Control Protocol, where it shows that TCP can't guarantee state consistency between endpoints and why this is the case), though it applies to any type of two-party communication where failures of communication are possible. A key concept in epistemic logic, this problem highlights the importance of common knowledge. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Raft (algorithm)
Raft is a consensus algorithm designed as an alternative to the Paxos family of algorithms. It was meant to be more understandable than Paxos by means of separation of logic, but it is also formally proven safe and offers some additional features. Raft offers a generic way to distribute a state machine across a cluster of computing systems, ensuring that each node in the cluster agrees upon the same series of state transitions. It has a number of open-source reference implementations, with full-specification implementations in Go, C++, Java, and Scala. It is named after Reliable, Replicated, Redundant, And Fault-Tolerant. Raft is not a Byzantine fault tolerant algorithm: the nodes trust the elected leader. Basics Raft achieves consensus via an elected leader. A server in a raft cluster is either a ''leader'' or a ''follower'', and can be a ''candidate'' in the precise case of an election (leader unavailable). The leader is responsible for log replication to the followers. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paxos Algorithm
Paxos ( gr, Παξός) is a Greek island in the Ionian Sea, lying just south of Corfu. As a group with the nearby island of Antipaxos and adjoining islets, it is also called by the plural form Paxi or Paxoi ( gr, Παξοί, pronounced in English and in Greek). The main town and the seat of the municipality is Gaios. The smallest of the seven main Ionian Islands (the Heptanese), Paxos has an area of , while the municipality has an area of and a population of about 2300. Paxos lies some 15 km from the southern tip of Corfu, and at about the same distance from the town of Parga on the mainland. It is connected by ferry lines from Igoumenitsa and Corfu with Gaios. The island is hilly, the highest point having an elevation of 230 m. In Greek mythology, Poseidon created the island by striking Corfu with his trident, so that he and his wife Amphitrite could have some peace and quiet. History Although it was possibly inhabited from prehistoric times, the Phoenicians ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Three-phase Commit Protocol
In computer networking and databases, the three-phase commit protocol (3PC) is a distributed algorithm which lets all nodes in a distributed system agree to commit a transaction. It is a more failure-resilient refinement of the two-phase commit protocol (2PC). Motivation A two-phase commit protocol cannot dependably recover from a failure of both the coordinator and a cohort member during the Commit phase. If only the coordinator had failed, and no cohort members had received a commit message, it could safely be inferred that no commit had happened. If, however, both the coordinator and a cohort member failed, it is possible that the failed cohort member was the first to be notified, and had actually done the commit. Even if a new coordinator is selected, it cannot confidently proceed with the operation until it has received an agreement from all cohort members, and hence must block until all cohort members respond. The three-phase commit protocol eliminates this problem by in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Yoav Raz
Joab (Hebrew Modern: ''Yōʼav'', Tiberian: ''Yōʼāḇ'') the son of Zeruiah, was the nephew of King David and the commander of his army, according to the Hebrew Bible. Name The name Joab is, like many other Hebrew names, theophoric - derived from YHVH (), the name of the God of Israel, and the Hebrew word 'av' (), meaning 'father'. It therefore means 'YHVH sfather'. Life Joab was the son of Zeruiah, a sister of king David (1 Chronicles 2:15-16). According to Josephus (Antiquities VII, 1, 3) his father was called Suri.Flavius Josephus, ''Antiquities of the Jews''Book VII, Chapter 1, 3 Joab had two brothers, Abishai and Asahel. Asahel was killed by Abner in combat, for which Joab took revenge by murdering Abner against David's wishes and shortly after David and Abner had secured peace between the House of David and the House of Saul (2 Samuel 2:13-3:21; 3:27). While 2 Samuel 3:27 explicitly states that Joab killed Abner "to avenge the blood of his brother Asahel", ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Network
A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are made up of telecommunication network technologies, based on physically wired, optical, and wireless radio-frequency methods that may be arranged in a variety of network topologies. The nodes of a computer network can include personal computers, servers, networking hardware, or other specialised or general-purpose hosts. They are identified by network addresses, and may have hostnames. Hostnames serve as memorable labels for the nodes, rarely changed after initial assignment. Network addresses serve for locating and identifying the nodes by communication protocols such as the Internet Protocol. Computer networks may be classified by many criteria, including the transmission medium used to carry signals, bandwidth, communications pro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tree (data Structure)
In computer science, a tree is a widely used abstract data type that represents a hierarchical tree structure with a set of connected nodes. Each node in the tree can be connected to many children (depending on the type of tree), but must be connected to exactly one parent, except for the ''root'' node, which has no parent. These constraints mean there are no cycles or "loops" (no node can be its own ancestor), and also that each child can be treated like the root node of its own subtree, making recursion a useful technique for tree traversal. In contrast to linear data structures, many trees cannot be represented by relationships between neighboring nodes in a single straight line. Binary trees are a commonly used type, which constrain the number of children for each parent to exactly two. When the order of the children is specified, this data structure corresponds to an ordered tree in graph theory. A value or pointer to other data may be associated with every node in th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Database
In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases spans formal techniques and practical considerations, including data modeling, efficient data representation and storage, query languages, security and privacy of sensitive data, and distributed computing issues, including supporting concurrent access and fault tolerance. A database management system (DBMS) is the software that interacts with end users, applications, and the database itself to capture and analyze the data. The DBMS software additionally encompasses the core facilities provided to administer the database. The sum total of the database, the DBMS and the associated applications can be referred to as a database system. Often the term "database" is also used loosely to refer to any of the DBMS, the database system or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X/Open XA
For transaction processing in computing, the X/Open XA standard (short for "eXtended Architecture") is a specification released in 1991 by X/Open (which later merged with The Open Group) for distributed transaction processing (DTP). Goals The goal of XA is to guarantee atomicity in "global transactions" that are executed across heterogeneous components. A ''transaction'' is a unit of work such as transferring money from one person to another. Distributed transactions update multiple data stores (such as databases, application servers, message queues, transactional caches, etc.) To guarantee integrity, XA uses a two-phase commit In transaction processing, databases, and computer networking, the two-phase commit protocol (2PC) is a type of atomic commitment protocol (ACP). It is a distributed algorithm that coordinates all the processes that participate in a distributed ... (2PC) to ensure that all of a transaction's changes either take effect (''commit'') or do not (''ro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Open Group
The Open Group is a global consortium that seeks to "enable the achievement of business objectives" by developing "open, vendor-neutral technology standards and certifications." It has over 840 member organizations and provides a number of services, including strategy, management, innovation and research, standards, certification, and test development. It was established in 1996 when X/Open merged with the Open Software Foundation. The Open Group is the certifying body for the UNIX trademark, and publishes the Single UNIX Specification technical standard, which extends the POSIX standards. The Open Group also develops and manages the TOGAF® standard, which is an industry standard enterprise architecture framework. Members The over 840 members include a range of technology vendors and buyers as well as government agencies, including, for example, Capgemini, Fujitsu, HPE, Orbus Software, IBM, Huawei, Philips, the U.S. Department of Defense, and NASA. There is no obligation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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