Big Data. Seifedine Kadry

of the server. Figure 2.13 shows a scale‐up architecture where the RAM capacity of the same machine is upgraded from 32 GB to 128 GB to meet the increasing demand.

Scaling‐out. The horizontal scalability adds new servers or components to meet the demand. The additional component added is termed as node. Big data technologies work on the basis of scaling out storage. Horizontal scaling enables the system to scale wider to meet the increasing demand. Scaling out storage uses low cost commodity hardware and storage components. The components can be added as required without much complexity. Multiple components connect together to work as a single entity. Figure 2.14 shows the scale‐out architecture where the capacity is increased by adding additional commodity hardware to the cluster to meet the increasing demand.

Figure 2.13 Scale‐up architecture.

Figure 2.14 Scale‐out architecture.

      Chapter 2 Refresher

      1 The set of loosely connected computers is called _____.LANWANWorkstationClusterAnswer:dExplanation: In a computer cluster all the participating computers work together on a particular task.

      2 Cluster computing is classified intoHigh‐availability clusterLoad‐balancing clusterBoth a and bNone of the aboveAnswer:c

      3 The computer cluster architecture emerged as a result of ____.ISAWorkstationSupercomputersDistributed systemsAnswer:dExplanation: A distributed system is a computer system spread out over a geographic area.

      4 Cluster adopts _______ mechanism to eliminate the service interruptions.Sharding ReplicationFailoverPartitionAnswer:c

      5 _______ is the process of switching to a redundant node upon the abnormal termination or failure of a previously active node.ShardingReplicationFailoverPartitionAnswer:c

      6 _______ adds more storage resources and CPU to increase capacity.Horizontal scalingVertical scalingPartitionAll of the mentionedAnswer:bExplanation: When the primary steps down, the MongoDB closes all client connections.

      7 _______ is the process of copying the same data blocks across multiple nodes.ReplicationPartitionShardingNone of the aboveAnswer:aExplanation: Replication is the process of copying the same data blocks across multiple nodes to overcome the loss of data when a node crashes.

      8 _______ is the process of dividing the data set and distributing the data over multiple servers.VerticalShardingPartitionAll of the mentionedAnswer:bExplanation: Sharding is the process of partitioning very large data sets into smaller and easily manageable chunks called shards.

      9 A sharded cluster is _______ to provide high availability.ReplicatedPartitionedClusteredNone of the aboveAnswer:aExplanation: Replication makes the system fault tolerant since the data is not lost when an individual node fails as the data is redundant across the nodes.

      10 NoSQL databases exhibit ______ properties.ACIDBASEBoth a and bNone of the aboveAnswer:b

Conceptual Short Questions with Answers

      1  What is a distributed file system? A distributed file system is an application that stores the files across cluster nodes and allows the clients to access the files from the cluster. Though physically the files are distributed across the nodes, logically it appears to the client as if the files are residing on their local machine.

      2  What is failover? Failover is the process of switching to a redundant node upon the abnormal termination or failure of a previously active node.

      3  What is the difference between failover and switch over? Failover is an automatic mechanism that does not require any human intervention. This differentiates it from the switch over operation, which essentially requires human intervention.

      4  What are the types of cluster? There are types of clusterHigh‐availability clusterLoad‐balancing cluster

      5  What is a high‐availability cluster? High availability clusters are designed to minimize downtime and provide uninterrupted service when nodes fail. Nodes in a highly available cluster must have access to a shared storage. Such systems are often used for failover and backup purposes.

      6  What is a load‐balancing cluster? Load balancing clusters are designed to distribute workloads across different cluster nodes to share the service load among the nodes. The main objective of load balancing is to optimize the use of resources, minimize response time, maximize throughput, and avoid overload on any one of the resources.

      7  What is a symmetric cluster? Symmetric cluster is a type of cluster structure in which each node functions as an individual computer capable of running applications.

      8  What is an asymmetric cluster? Asymmetric cluster is a type of cluster structure in which one machine acts as the head node, and it serves as the gateway between the user and the remaining nodes.

      9  What is sharding? Sharding is the process of partitioning very large data sets into smaller and easily manageable chunks called shards. The partitioned shards are stored by distributing them across multiple machines called nodes. No two shards of the same file are stored in the same node, each shard occupies separate nodes, and the shards spread across multiple nodes collectively constitute the data set.

      10  What is Replication? Replication is the process of copying the same data blocks across multiple nodes to overcome the loss of data when a node crashes. The copy of a data block is called replica. Replication makes the system fault tolerant since the data is not lost when an individual node fails as the data is redundant across the nodes.

      11  What is the difference between replication and sharding? Replication copies the same data blocks across multiple nodes whereas sharding copies different data across different nodes.

      12  What is the master‐slave model? Master‐slave configuration is a model where one centralized device known as the master controls one or more devices known as slaves.

      13  What is the peer‐to‐peer model? In a peer‐to‐peer configuration there is no master‐slave concept, all the nodes have the same responsibility and are at the same level.

      14  What is scaling up? Scaling‐up, the vertical scalability, adds more resources to the existing server to increase its capacity to hold more data. The resources can be computation power, hard drive, RAM, and so on. This type of scaling is limited to the maximum scaling capacity of the server.

      15  What is Scaling‐out? Scaling out, the horizontal scalability, adds new servers or components to meet the demand. The additional component added is termed as node. Big data technologies work on the basis of scaling out storage. Horizontal scaling enables the system to scale wider to meet the increasing demand. Scaling out storage uses low cost commodity hardware and storage components. The components can be added as required without much complexity. Multiple components connect together to work as a single entity.

      16  What is a NewSQL database? A NewSQL database is designed to provide scalable performance similar to that of NoSQL systems combining the ACID (atomicity, consistency, isolation, and durability), properties of a traditional database management system.