Cassandra System in Facebook

Cassandra System in Facebook Cassandra was designed to accomplish scalability and availability for the Inbox Storage problem. It was a system developed for Facebook. It would need to handle more than a billion write operations. It would also need to scale with the number of users. The data centers which serve the users are distributed across earths geography. Figure 1 Cassandra Symbol In order to keep the search latencies down, it would be necessary for the users to replicate the data over the data centers. Facebook has installed Cassandra as its back end storage system. This is done for multiple services available at Facebook. Distributed file systems have hierarchal name spaces. The existing systems allow operations which are disconnected. They are also strong against general issues like outages and network partitions. Conflicts resolution is different in different systems in Coda and Ficus there is level conflict resolution. Application level resolution is allowed by Bayou. Traditional relational databases seek at providing guarantee of consistent replicated data. Amazon uses the Dynamo storage system for storing and retrieving user details. It uses the Gossip member protocol to maintain node data. Vector clock scheme is used to detect conflict. It has more preference for client side conflict resolution mechanism. In systems which need to handle a high write through put, Dynamo can be disadvantages as read would be needed to manage the vector stamps. Casandra is a non-relational database. It has a distributed multi-dimensional map. This map is indexed by a key. The value which the key points to is highly structured. The size of the row key is a string which has no restrictions. It has size corresponding to 16 to 36 bytes. Like the Big table system, the columns are grouped together into sets. These sets are called as column families. The column families are divided into two type: 1) Simple column families These are the normal column families 2) Super column families The super family has a column family inside a column family. Sorted order of the column can be specified. The inbox display usually displays the messages in time sorted fashion. This can be used by Cassandra as it allows the sorting over the columns by time or by name. The results are displayed in easily for the inbox searches in a time sorted manner. The syntax used to access column family is column_family:column. For a super column family it is column_family: super_column: column. Cassandra cluster is used a part of an application. They are then managed as a part of a service. All the deployments have jsut one table in their schema. But it does support the notion of multiple tables. The API of Cassandra has the below three basic commands: insert (table, key, rowMutation) get (table, key, columnName) delete (table, key, columnName) column name stands for a super column family or simple column family, a specific column in the column family. Consider the architecture of storage system involves plenty of complicated scenarios. Many factors need to be handled such as configuration management, robustness, scalability, For this document we consider primary features of Cassandra that includes membership, partitioning, failure handling, scalability, replication For the various read write requests, the module works in synchrony. In order to confirm the completion of writes, the system routes requests to replica. Reads are handled differently. System reroutes the requests to the nearest replica / route and awaits a quorum of responses. Partitioning Ability to increase scaling is a critical feature provided by Cassandra. This is provided in dynamic way. In the cluster, the partition takes place over the storage hosts. Consistent hashing and also preserving has functions are performed to take care of partitioning. Consider the consistent hashing approach. Here the largest hash value covers the smallest hash value. All nodes are then provided another adhoc value represented by the position of ring. Application provides the key with Cassandra leverages that to move requests. Responsibility is established at a node level around the ring region. Main benefit of this approach is that transition of node impacts only the neighboring node, whereas other nodes are not impacted. There does exist some difficulties for this approach. There is lack of uniform data and load distributions due to the adhoc positions of nodes around the ring. The approach ignores the differences in performances of nodes. Replication In order to increase the durability and availability, Cassandra provides replication. For this purpose, all data item is copied over at N hosts. Each node is conscious aware of other nodes in network, thus high durability is established. Each row is replicated across various data centers that are further synced with very high speed network links. Bootstrapping A configuration is maintained for a node joining the cluster. Configuration file provides the necessary contact points to join the cluster. These are known as seeds. A service can also provide such configuration. Zookeeper is one of them. Scaling the Cluster Consider the case of adding a new node to system. For this purpose, a token is assigned to it. Goal is to reduce load on heavily loaded node. New node is split on a range wherein previous node was assigned for. Web dashboards are provided that can perform above tasks. These can also be achieved through command line utility. Local Persistence Local file system helps provide the necessary local persistence for Cassandra. For recovering data efficiently, disks are used to represent data. There are standard write operations. These include ability to commit and update into a data structure. After successful commit log, then write to in-memory data structure is performed. Implementation Details The Cassandra process on a single machine is primarily consists The process involves clustering, fault identification and storage modules. These apply for a specific machine. There exists event driven items. These split the message across the process pipeline and also task pipeline. These are performed across various steps as part of architecture. JAVA is primary source and all modules are built from scratch using Java. For the clustering and fault detection module, input output that is of type non-blocking is built upon. There are few lessons that were learnt over maintaining Cassandra. New features should be added after understanding its implications over the system. Few scenarios are stated below: 7TB of the data needed to be indexed for 00M users. It was extracted, transformed an loaded into the Cassandra database using Map reduce jobs. The Cassandra instance juts becomes a load over the network bandwidth as some of the data was sent over serialized data over the Cassandra network. Application requirement is to have an atomic operation per key per replica. Storage system features, architecture and implementation is described including partitioning, replication, bootstrapping, scaling, persistence and durability. These are explained through Cassandras perspective which provides those benefits. [1] Avinash Lakshman, Facebook Prashant Malik, Facebook, Cassandra A Decentralized Structured Storage System

Chinese Literature Essay

The first short story under consideration is â€Å"Iron Child† by Mo Yan. The piece of literature deals with industrialization of China, which aimed at establishing the socialist model of political system of this country in the beginning of the second half of the twentieth century. The outcomes of the political transformation of China, particularly, child labor, are described in the story. The story â€Å"Iron Child† is narrated by a five-year-old boy (Yan n.pag.). Another short story under analysis is â€Å"Dogshit Food† by Liu Heng. The events of this story take place in the period of the so-called Great Leap Forward (1958). â€Å"Dogshit Food† deals predominantly with the issues of social life in China and political transformation after the World War II. The author emphasizes the human perception of beauty and ethical aspect of interpersonal relations. The story is being delivered in the third person singular, which indicates author’s narrative. The protagonist of the novel is Yang Tiankuan (Heng n.pag.). In spite of thematic diversity and differences in the formal realization of subject matter in both short-stories, â€Å"Dogshit Food† by Liu Heng and â€Å"Iron Child† by Mo Yan, they have a wide range of similarities. In his short story â€Å"Iron Child†, Mo Yan deals with the issues of industrialization of China establishing the socialist model of political system. The writer also reflects upon the most acute and burning social issues, particularly, child labor. It should be mentioned that Mo Yan creates the reality in which children appeared to be the most vulnerable in  the face of decisions and choices of adults. The general tone of the novel is gloomy. The pace of revolving the plot is predominantly moderate, gravitating towards acceleration. The surrealist vision gives this short story the flavor of reminiscence, since the author, apparently, is recalling and reconsidering his childhood. The aspect of the surrealist vision is embodied in the Iron Child who is the protagonist’s friend. Iron Child is endowed with extraordinary abilities of consuming iron (Yan n.pag.). On the other hand, â€Å"Dogshit Food† by Liu Heng, above all, accentuates the inter-personal relations between Yang Tiankuan and his wife and Yang Tiankuan and the rest of community inhabiting the Flood Water Valley. According to the short story, the negative effect of reformatting the agriculture and economy of China is related to the issue of malnutrition. Apparently, the author is drawing a parallel between the affliction and the person’s character. The conflict between the appearance, the outer surface, and person’s inner world is revealed through the lens of Yang Tiankuan’s wife. Namely, the author analyzes the way she treats Yang Tiankuan and others and, consequently, the way she perceives the world (Heng n.pag.). Therefore, the issues dealt in both novels are social life in China in the age of the Great Leap Forward, childhood and the status of children in Chinese society, interpersonal relations, human perception, and understanding the beauty. The essence of social issues and their outcomes and, as a result, the cause-effect relations dealt with in both short stories constitute the commonness between these particular pieces of literature. Another important observation to be made concerns the aspect of distinctiveness and autonomy of Chinese literature in general and Chinese prose of the twentieth century in particular. The phenomenon of distinctiveness and autonomy of Chinese literature was predetermined by the geographical position of China as well as scientific, cultural, and political separateness of this region from the rest of the world. Coalescence, i.e. loss of individuality, of the Chinese historic-cultural frontier in Asia represented itself as a notable fact common to the second half of the twentieth century. Mo Yan and Liu Heng’s positions supported Chinese identity in the context of culture by all means. Considering the current situation, it is important to admit the process of introducing the realities of the Western world to East and China in particular. They were assimilated into Eastern ground. Mo Yan and Liu Heng’s short stories were called, above all, to communicate the idea of cultural identity to the audience across the world. In other words, these particular pieces of literature have no target audience. In its turn, the absence of target audiences indicates both self-sufficiency and self-sustainment of art in general and literature in particular. Self-sufficiency and self-sustainment are the markers of the postmodern art, philosophy and the concept of world. However, social determination of both pieces of art is obvious as far as their subject matter is concerned. In my considered opinion, the issues of identity, assimilation and social determination presented in both â€Å"Dogshit Food† by Liu Heng and Mo Yan’s â€Å"Iron Child† are important in terms of investigating and analyzing. Works Cited Heng, Liu. â€Å"Dogshit Food.† _Fiction Since 1976._ Trans. Deride Sabina Knight. N.p., n.d. 366 – 378. Print. Yan, Mo. â€Å"Iron Child.† _Fiction Since 1976._ Trans. Howad Goldblatt. N.p., n.d. 367 – 387. Print.

The Battle Of The Bulge - 3845 Words

Battle of the Bulge The Battle of the Bulge started in the winter December 16th 1944 – 1945 towards the end of World War II. It was the last major Nazi attack against the Allies in World War II. The Battle of the Bulge was the last chance effort by Hitler to split the alliance between Britain, France and America in two. Adolf Hitler believed that the western sector of Europe was weak in addition, if he attacked with a successful defeat, it would break up the alliance. Hitler ordered a major attack on mostly the American forces. Hitler’s goal was to destroy all Allied armies to force the Western Allies to negotiate a peace treaty in his favor. That attack was officially known as the Battle of the Ardennes by the U.S Army. When the Germans first attacked it created a bulge in the Americans Allied front line, which is now known as the Battle of the Bulge. By the end of January 1945, America units had recovered all the ground they lost. Hitler’s plan was to attack with such a great force using three armies against the United States Allies, which in his head would destroy the pipeline in which the majority of supplies were reaching our Allies. The German final plan was to attack and capture Antwerp, which would divide the British and American armies that would deprive the much needed pipeline which the Allies used for supplies. Choosing this plan of action, Hitler used Walter Model and Gerd von Rundstedt to execute this plan. To move forward with thisShow MoreRelatedThe Battle of the Bulge757 Words   |  3 Pages to eliminate the bulge in the American line. This success was largely due to General Patton’s third army, that attacked from the North and the South. On January 8, 1945, the German forces began to pull out of the Bulge. As the Americans advanced, they continued to erase all German gains. By the end of January, 1945, all territory that was captured by the Germans was back under Allied control (â€Å"Battle of the Bulge†). The Battle of the bulge was one of the most difficult battles of the war for theRead MoreThe Battle Of The Bulge1089 Words   |  5 PagesBattle of the Bulge The United States remains a country with a rich history in several issues including strong military activities including their incursion in Iraq, Afghanistan and other volatile countries around the world. However, the devastations of the Battle of the Bulge make it as one of the deadliest and bloodiest wars that the U.S has ever witnessed in history. It led to various war tactics with artillery emerging from it and other military operation challenges. Despite its unpredictableRead MoreThe Battle Of The Bulge1098 Words   |  5 PagesThe Battle of the Bulge was one of the Bloodiest battles of World War II with around 175,000 total casualties and played a key role in ending the War. The Battle started as a German surprise attack on Allied Forces along an 80-mile front in the Ardennes Forest of southern Belgium. The Germans initially had a great deal of success in their attack but through a series of Allied counter attacks the Allied Forces were able to cripple the German Forces. The Field Artillery played a crucial role inRead MoreThe Battle Of The Bulge2131 Words   |  9 PagesThe Battle of the Bulge was the largest battle on the Western Front of World War Two. At the largest point of the battle it involved over 1.1 million men. The battle was started when the Germans launched Operation Watch on the Rhine. The main objective of this operation was to capture the American held harbor of Antwerp which is Belgium. Ever since the invasion of Normandy the allies had had problems bringing supplies up to the front. Every time the Germans left a city with a harbor in it they sabotagedRead MoreThe Battle Of The Bulge1712 Words   |  7 Pages Battle of the Bulge Christopher Adams NCOA SLC 15-005 Battle of the Bulge Introduction The Battle of the Bulge, a massive German counteroffensive which began in December 1944, ultimately produced the largest casualty rate in any one battle throughout World War II. The Allied Forces alone lost almost 80,000 at the Battle of the Bulge. This casualty rate could have been much higher if Hitler would’ve grasped the importance and value of supply and logisticalRead MoreThe Battle Of The Bulge1077 Words   |  5 PagesBattle of the Bulge The Battle of the Bulge is remembered as Adolf Hitler’s final effort to escape total defeat during World War II (WWII). His initial efforts were successful, however the Allied force commanders proved superior through there demonstrated adaptive and decisive decision making. These actions helped to overcome the military force and military intelligence failures during the battle. If these failures had been avoided, the Germans would have been defeated much quickerRead MoreBattle of the Bulge1611 Words   |  7 PagesThe battle of the bulge The battle of the bulge was Hitlers last chance to win the war or at least make the allies go for a treaty. He did this because his forces were being pushed back into Germany and soon they would run out of supplies and other resources for war. Hitler thought of this bold plain when he recalled how a German hero Frederick the great was facing defeat, Frederick went on a offensive attack at his foe who had superior numbers but the bold moved worked and Hitler thought heRead MoreThe Battle Of The Bulge1630 Words   |  7 PagesImagine hundreds of thousands of soldiers fighting in blizzard conditions, both sides fighting for their country, The Battle of the Bulge was one of the largest battles of the war and proved to be one of the most important. Some people ask how the Allied forces were able to stop the seemingly unbeatable Nazi war machine, this battle would be the last major offensive by the Third Reich in attempt to change the tides of the Second World War. The Allied forces were about to be a part of the true terrorsRead MoreThe Battle Of The Bulge1647 Words   |  7 PagesThe Battle of the Bulge stands as the largest battle fought between the Allied and Axis forces on the Western Front during World War II. This battle was a German offensive intended to drive a wedge between the American and British armies in France and the Low Countries and capture the port of Antwerp in the Netherlands to deny the Allies use of the port facilities. The battle also known as the Ardennes Offensive, took place in the Ardennes Forest of Luxembourg and Belgium. The battle waged duringRead MoreThe Battle Of The Bulge1388 Words   |  6 PagesWhen Eisenhower summons 10th Armored Division to Bastogne, Patton exercises disciplined initiative in setting the stage for victory at the Battle of the Bulge. Before Patton is summoned to Verdun, he set the conditions for his forces to break away from the battle in the Saar River Valley and move toward Bastogne. Patton initially protests the order to send the 10th Armored Division to Bastogne. Losing an entire division would weaken his effort to Invade Germany in the Saar. However, Patton finally

Literature Review On Police Brutality - 1105 Words

Literature Review Police and community relations has always been a work in progress, some communities are more challenging than others. There are various factors that impact the relationship police have with civilians such as geographical location, race, gender, personal experience and in personal ones as well. In the last few years police and the African American community on a national level been more disconnected due to a pattern of unforeseen circumstances of unarmed black men being shot and killed by officers, that end up serving no jail or repercussion besides paid administrative leave. Police brutality is defined by The Law Dictionary as the use of force used unnecessarily. â€Å"Force that is used beyond what is necessary to handle the†¦show more content†¦Police Brutality Against African Americans Many factors affect how and why African American perception is negative some underlining factors are face to face encounters, procedural justice, historical as well as having a positive in teraction with an officer (Weitzer,2015). African American that being stopped and spoken to in a demeaning manner, lack of explanation to why they were stopped and inability to ask questions and explain what happen impacted their feelings. Though positive interactions help the general it does not necessarily help because they are outside influence such as the media and accounts of family and friends. (Jacob, 1971, Skogan 2016, Weitzer,2015). Racial Bias are a direct correlation to police violence against African Americans, stereotypes perpetuated by social constructions and media representation along with individual prejudice help by police officers view African Americans as a threat especially African American men. Police trust this ideology of â€Å"threat† to assist in their use of excessive force against African Americans to comply. (Tyler, 2011; Tyler et al., 2015, Skinner, Haas,2016). Police Brutality and African American Men In recent years the killings of African American men have increased, especially those of unarmed black men. Between 2010 and 2012 it was reported that Blacks males were 21 times more likely to beShow MoreRelatedPolice Brutality And Why Is It Important Right Now? Essay926 Words   |  4 PagesIntroduction What is police brutality and why is it important right now? Police brutality is the use of excessive force carried out by a law enforcement official. Lately, various incidents of police brutality have surfaced in the news, but this is nothing new. Past incidents including the death of Michael Brown in Ferguson, Missouri brought serious social issues to the frontlines. Michael Brown was an unarmed black teenager who was shot and killed by a white male. Other incidents include the deathRead MoreShould Police Officers Be Required For Where Body Cameras?1479 Words   |  6 Pages Should Police Officers be required to where Body Cameras Ken Davis BUSI600 Section # BO5 June 21, 2015 Abstract The pedigree of this literary review will outline some of the dimensions and elements that provide empirical research by reliable researchers using reliable methods. The purpose of this paper is threefold: The first purpose is to review the communication and organizational literature on authority in order to illustrate how police brutality assist and continues toRead MoreThe Violence Of Police Brutality Essay1126 Words   |  5 Pagescitizens receive from the police in addition to how the citizens interact with police. Video footage has shown police brutality that is sometimes questionable, which often dictates on the how the community views them by causing tension. Accusations of Police brutality is nothing new but it isn’t until recently that it is being recorded and it is difficult to correct the actions of someone if there is not enough evidence provided. Recent advancements in technology police accountable for their actionsRead MoreThe Social Problem Of Police Brutality1458 Words   |  6 Pagesproblem I would like to conduct sociological research on is the use of excessive force used by members of the police department in recent unconscionable shootings of unarmed civilians. With all the recent attention that the people of Ferguson Missouri and New York City have been able to rise on this issue, making it a media sensation, it seemed like a good topic to discuss. Police brutality is an egregious, ongoing problem in our society that, until just recently, has been accepted as a sad fact ofRead MoreThe Violence Of Police Officers Essay1431 Words   |  6 Pagesmotivated police brutality and societal discrimination. Though his efforts were not in vain, today’s media representation of law enforcement impacts the societal cultivation of police officers in a negative way. Media outlets, in the forms of television, radio, or social websites, create a cynical view of polic e officers, which influences societal beliefs and creates negative connotations. These days, police are often stereotyped as aggressive, corrupt beings. The growing hatred for police officersRead MoreBlack Panthers Platform: Takin it to the Streets Essay example1141 Words   |  5 Pagesmovement requests are stated in the â€Å"Black Panther Platform†. The theme of the literature was to clearly state what was requested by them and there people. The Black Panthers wanted the opportunity to determine the destiny of themselves which they believed shall make them free. The Black Panthers Platform was created to clearly state what black community’s wanted to see change and to show the issues of racism and police brutality. The military wants to draft African American men to fight and to risk theirRead MoreThe Between Democracy, Its Processes, And Policing Are Well Established Across A Wide Variety Of Academic Disciplines1562 Words   |  7 PagesThe connections between democracy, its processes, and policing are well established across a wide variety of academic disciplines. Political scientists and economists have developed a literature discussing the various forms police forces take and their positions within certain regime types. Separate from theory regarding democratization and security, like Sklansky’s (2005) work , a great deal of scholarly papers have been written regarding riots and civil disruption. For example, Gunning (1972)Read MoreSocial Media Activism, Centered On Police Brutality1180 Words   |  5 Pages Has Social Media Activism, Centered On Police Brutality in African-American Communities Producing Sustainable Change? Simona M. Young University of Southern California Over the last year, the media has done an excellent job in bringing national exposure to the culture of police brutality within African-American communities. Fortunately, social media – alongside the growing accessibility to smartphones – has assisted in bringing these intentional violations to the forefront ofRead MoreThe Prison Industrial Complex And Police Brutality Essay1522 Words   |  7 Pages Literature Review Over the last few years the hashtag Black Lives Matter has become a hot topic. This organization is trying to bring awareness to the issues that people of color face. They are also trying to bring â€Å"real† equality to people of color. Many non-people of color feel like black people are no longer oppressed. I plan to delve into systematic racism and how it is a real issue. I will be looking into the prison industrial complex, and police brutality examining how it relates back to slaveryRead MorePolice Misconduct And The Police Subculture Essay2033 Words   |  9 PagesPolice Misconduct and the Police Subculture Police misconduct has remained a serious problem since the beginning of policing. Police officers have grant especial power that if not use in an ethical way can end in police misconduct. Police officers are the ones who are supposed to protect and serve the communities, so it is horrible to know that some officers engage in misconduct behaviors that are hampering the trust and confidence that people in society have on them. Some police officers do not