Category Archives: Spark

What is hdfs (Tutorial Day 9)

HDFS stands for Hadoop Distributed File System. It is designed to provide a fault-tolerant file system designed to run on commodity hardware. It uses a master/slave architecture in which one device (the master) controls one or more other devices (the slaves). The HDFS cluster consists of a single NameNode and a master server manages the file system namespace and regulates access to files.

Namenode is the centerpiece or master node of  HDFS. It only stores the metadata of HDFS and no data – means the directory tree of all files in the file system, and tracks the files across the cluster. The data is actually stored in the DataNodes. NN knows the list of the blocks and its location for any given file in HDFS. With this information it knows how to construct the file from blocks. NN is so critical that if its down or has any fault, HDFS/Hadoop cluster is inaccessible. NN is a single point of failure in Hadoop cluster. NameNode is usually configured with a lot of memory (RAM). We generally have Secondary NN to cover up this kind of failures, but they are manual start-up.

DataNode is known as Slave nodes & is responsible for storing the actual data in HDFS. NN & DN are in constant communication. When a DataNode starts up it announce itself to the NN along with the list of blocks it is responsible for. When a DataNode is down, it does not affect the availability of data or the cluster. NN will arrange for replication for the blocks managed by the DN that is not available. DataNode is usually configured with a lot of hard disk space. Because the actual data is stored in the DataNode.

More features of HDFs:

  • Single Master node, along with secondary Namenode (in Hadoop 1.x, secondary NN is manual start up, whereas in Hadoop 2.x we have automated failure recovery using secondary namenode)
  • Multiple Data nodes cluster (also called slave deamons)
  • Every block has a fixed size
  • Example: We have a NYSE data file of 39 mb. So if my datanode has block size defined as 27mb each, then we will get 2 files created in HDFS .One of 27mb and one of 12mb


HDFS Architecture 



                                                                                             Image credit: Google
  • Client is a application running on our machines which is used to interact with NN and DN, Job tracker etc. It is used for User interaction and is called HDFS client.
  • A Hadoop Cluster is a collection of racks. A rack is a collection of 30 or 40 nodes that are physically stored close together and are all connected to the same network switch. Network bandwidth between any two nodes in rack is greater than bandwidth between two nodes on different racks. In other words, a rack is the hard-disk or storage area of HDFS.
  • Client interacts with NN using SSH and not http.
  • To maintain fault tolerance on Hadoop system, we maintain replicate data. Minimum no. of replicas required by HDFS is 3. It can configured by admin too, but redundancy is necessary to be done
  • When a file is written to HDFS, it is split up into big chucks called data blocks, whose size is controlled by the parameter dfs.block.size in the config file hdfs-site.xml (default is 64MB). All blocks in a file except the last block are the same size . Each block is stored on one or more Data nodes, controlled by the parameter dfs.replication in the same file (in most of this post – set to 3, which is the default). Each copy of a block is called a replica.The blocks of a file are replicated for fault tolerance. Files in HDFS are write-once and have strictly one writer at any time.
  • Since there are 3 nodes, when we send the MapReduce programs, calculations will be done only on the original data. The master node will know which node exactly has that particular data. In case, if one of the nodes is not responding, it is assumed to be failed. Only then, the required calculation will be done on the second replica.

Process to read/write file into hdfs

When writing data to an HDFS file, its first written to local cache. When the cache reaches a block size (default 64MB), the client request the list of DN from the NN. This list contains all the DN that will host a replica of that block. The number of DN replication is default to 3. The client then organizes a pipeline from DN-to-DN and flushes the data block to the first DN (as shown in image below). The first DataNode starts receiving the data in small portions (file system block size 4 KB), writes each portion to its local repository and transfers the same portion to the second DataNode in the list. The second DataNode, in turn starts receiving each portion of the data block, writes that portion to its repository and then flushes the same portion to the third DataNode. Finally, the third DataNode writes the data to its local repository. Thus, a DN can be receiving data from the previous one in the pipeline and at the same time forwarding data to the next one in the pipeline. When the first block is filled, the client requests new DN to host replicas of the next block. A new pipeline is organized, and the client sends the further bytes of the file. This flow continues till last block of the file.


                                                                                                    Image credit: google

Advantages of HDFS

  • Suitable for applications with large datasets only. If you have small data sets, then its too expensive to store them
  • Inexpensive as filesystem relies on commodity storage disks that are much less expensive than the storage media used for enterprise grade storage
  • Highly Fault Tolerant
  • High throughput ( time taken to access , read data. Similar to example explained below)

HDFS is optimized for MapReduce workloads. It provides very high performance for sequential reads and writes, which is the typical access pattern in MapReduce jobs.

Learn more about Hadoop Installation, here !!


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What is Resilient Distributed Datasets (RDDs) ? (Day 3)

Spark’s primary core abstraction is called Resilient Distributed Dataset or RDD.It is designed to support in-memory data storage, distributed across a cluster in a manner that is Resilient,fault-tolerant and efficient. RDD are Resilient as it relies on lineage graph , whenever there is  a failure in system, they can recompute themselves using the prior information. Similarly Fault-tolerance is achieved, in part, by tracking the lineage of transformations applied to coarse grained sets of data. Efficiency is achieved through parallelization of processing across multiple nodes in the cluster, and minimization of data replication between those nodes.

In a layman language, you can RDD is representation of the data that’s coming into your system in an object format & allows you to do computation on it.”

Spark RDD’s can reference to a dataset in an external storage system, such as a shared filesystem, HDFS, HBase, or any data source offering a Hadoop InputFormat. Also we can define it as, just a distributed collection of elements that is parallelized across the cluster. Once data is loaded into an RDD, two basic types of operation can be carried out.. Transformations and Actions.

Transformations are those that do not return a value. In fact, nothing is evaluated during the definition of these transformation statements. It just creates a new RDD by changing the original through processes such as mapping, filtering, and more. The fault tolerance aspect of RDDs allows Spark to reconstruct the transformations used to build the lineage to get back the lost data.

Actions are when the transformations get evaluated along with the action that is called for that RDD. Actions return values. For example, you can do a count on a RDD, to get the number of elements within and that value is returned.

The original RDD remains unchanged throughout. The chain of transformations from RDD1 to RDDn are logged, and can be repeated in the event of data loss or the failure of a cluster node.RDDs can be persistent in order to cache a dataset in memory across operations. This allows future actions to be much faster, by as much as ten times.
Spark’s cache is fault-tolerant in that if any partition of an RDD is lost, it will automatically be recomputed by using the original transformations. For example, let’s say a node goes offline. All it needs to do when it comes back online is to re-evaluate the graph to where it left off. Caching is provided with Spark to enable the processing to happen in memory. If it does not fit in memory, it will spill to disk.
Interesting thing about Spark is , it’s lazy evaluation.  This is because RDD are not loaded into system as in when the system encounters an RDD , but only done when an Action is supposed to be performed. So to understand this concept, lets take an example:
  • We read a text file and load the data into new created RDD ‘m’   {scala>  val m=sc.textfile (“abc.txt”)  } . This step is interpreted by Spark and an DAG is created that tells it to read data from file and push it in RDD format. An RDD is made of multiple partitions. By default, the minimum # of partitions in an RDD will be two. However, this is customizable and will be different in vendor distributions of Spark. For example, when creating an RDD out of an HDFS file, each block in the file feeds one RDD partition, so a file with 30 unique blocks will create an RDD with 30 partitions. Or in Cassandra, every 100,000 rows get loaded into one RDD partition. So, a Cassandra table with 1 million rows will generate an RDD with 10 partitions.
  • Next step is to display the first item in this RDD,  {scala>  m.first() }
  • Now lets use the .filter() transformation on the ‘m‘ RDD to return a new RDD named “linesWithApache“, which will contain a subset of the items in the file (only the ones containing the string “Apache”: {scala> val linesWithApache = m.filter(line => line.contains(“Apache”))}
  • Now lets use an Action to find no. of lines with Apache word.  {scala> linesWithApache.count()}
  • To further see these lines, you can use .collect()  Action.  {scala> linesWithApache.collect()  }
Learn How Spark actually works? Click here


Spark Components..Architecture (Day 2)

So here we are today…in Day 2  tutorial for Spark learning. As we all know, that Spark is a top-level project of the Apache Software Foundation, designed to be used with a range of programming languages and on a variety of architectures. Spark’s speed, simplicity, and broad support for existing development environments and storage systems make it increasingly popular with a wide range of developers, and relatively accessible to those learning to work with it for the first time.

To learn Spark easily and incorporate into existing applications as straightforwardly as possible., its developed to support many programming languages like Java, Python, Scala, SQL & R. Spark is easy to download and install on a laptop or virtual machine. Spark was built to be able to run in a couple different ways: standalone, or part of a cluster.For production workloads that are operating at scale, Spark will require to run on an big data cluster. These clusters are often also used for Hadoop jobs, and Hadoop’s YARN resource manager will generally be used to manage that Hadoop cluster (including Spark).  Spark can also run just as easily on clusters controlled by Apache Mesos.A series of scripts bundled with current releases of Spark simplify the process of launching Spark on Amazon Web Services’ Elastic Compute Cloud (EC2).

Spark Architecture

The Spark architecture or stack currently is comprised of Spark Core and four libraries that are optimized to address the requirements of four different use cases.Individual applications will typically require Spark Core and at least one of these libraries.

What are Spark Components?

Spark core: Its is a general-purpose system providing basic functionality like task scheduling, distributing,fault recovery, interacting with storage systems and monitoring of the applications across a cluster. Spark Core is also home to the API that defines resilient distributed datasets (RDDs), which is Spark’s main programming abstraction.

Then you have the components on top of the core that are designed to interoperate closely.Benefit of such a stack is that all the higher layer components will inherit the improvements made at the lower layers. Example: Optimization to the Spark Core will speed up the SQL, the streaming, the machine learning and the graph processing libraries as well.

  1. Spark Streaming : This module enables scalable and fault-tolerant processing of streaming data, and can integrate with established sources of data streams like Flume. Examples of data streams include log files generated by production web servers, or queues of messages containing status updates posted by users of a web service.
  2. Spark SQL: This module is for working with structured data. It allows querying data via SQL as well as the Apache Hive variant of SQL—called the Hive Query Language (HQL)—and it supports many sources of data, including Hive tables, Parquet, and JSON.Spark SQL also supports JDBC and ODBC connections, enabling a degree of integration with existing databases, data warehouses and business intelligence tools.
  3. GRaphX : It supports analysis of and computation over graphs of data (e.g., a social network’s friend graph) and performing graph-parallel computations. Like Spark Streaming and Spark SQL, it also extends the Spark RDD API, allowing us to create a directed graph with arbitrary properties attached to each vertex and edge. It provides various operators for manipulating graphs (e.g., subgraph and mapVertices) and a library of common graph algorithms (e.g., PageRank and triangle counting).
  4. Spark Mlib : Spark comes with a library containing common machine learning (ML) functionality, called MLlib. It provides multiple types of machine learning algorithms, including classification, regression, clustering, and collaborative filtering, as well as supporting functionality such as model evaluation and data import.

What is Resilient Distributed Datasets (RDDs)? Click here to learn Day 3 tutorial 🙂

What is it replacing Hadoop ? (Day1)

Spark Framework is a simple Java web framework built for fast computation. It is a free and open-source software  & an alternative to other Java web application frameworks such as JAX-RS and Spring MVC. It was started in 2009 at Berkeley.


To define, Spark is a cluster-computing framework, which means that it competes more with MapReduce than with the entire Hadoop ecosystem. It actually extends MR model to support more computation ways like interactive/iterative algos, queries, stream processing, graph processing etc. It is designed to be highly accessible, offering simple API in languages like Python, Java, Scala & SQL.One of the main features Spark offers for speed is the ability to run computations in memory, but the system is also more efficient than MapReduce for complex applications running on disk.

Is Spark a Hadoop module?

We see Spark is listed as a module on Hadoop’s project page, but Spark also has its own page because, while it can run in Hadoop clusters through YARN, it also has a standalone mode. So Spark is independent. By default there is no storage mechanism in Spark, so to store data, need fast and scalable file system. Hence uses S3 or HDFS or any other file system, but if you use Hadoop it’s very low cost.

Spark runs on Hadoop, Mesos, standalone, or in the cloud. It can access diverse data sources including HDFS, Cassandra, HBase, and S3. You can run Spark using its standalone cluster mode, on EC2, on Hadoop YARN, or on Apache Mesos. However, as time goes on, some big data scientists expect Spark to diverge and perhaps replace Hadoop, especially in instances where faster access to processed data is critical.

(Source: Internet)

Hadoop vs Spark

A direct comparison of Hadoop and Spark is difficult because they do many of the same things, but are also non-overlapping in some areas.The most important thing to remember about Hadoop and Spark is that their use is not an either-or scenario because they are not mutually exclusive. Nor is one necessarily a drop-in replacement for the other. The two are compatible with each other and that makes their pairing an extremely powerful solution for a variety of big data applications.So we can compare them on some below points:

  1. Data Processing Engine/Operators: Hadoop originally was designed to handle crawling and searching billions of web pages and collecting their information into a database. For this it uses Map reduce,which is a batch-processing engine. MapReduce operates in sequential steps by reading data from the cluster, performing its operation on the data, writing the results back to the cluster, reading updated data from the cluster, performing the next data operation, writing those results back to the cluster and so on. But Spark is a cluster-computing framework,Which performs similar operations, but it does so in a single step and in memory. It reads data from the cluster, performs its operation (Filter/map/join/groupby) on the data, and then writes it back to the cluster.
  2. File System: Spark has no file management and therefor must rely on Hadoop’s Distributed File System (HDFS) or some other solution like S3, Tachyon.
  3. Speed/Performance: Spark’s in-memory processing admit that Spark is very fast (Up to 100 times faster than Hadoop MapReduce), Spark can also perform batch processing, however, it really excels at streaming workloads, interactive queries, and machine-based learning.The reason that Spark is so fast is that it processes everything in memory. Yes, it can also use disk for data that doesn’t all fit into memory.Spark uses memory and can use disk for processing, whereas MapReduce is strictly disk-based. Example: Internet of Things sensors, log monitoring, security analytics all require Spark for faster computation.
  4. Storage: MapReduce uses persistent storage and Spark uses Resilient Distributed Datasets (RDDs)
  5. Ease of Use: Spark is well known for its performance, but it’s also somewhat well known for its ease of use in that it comes with user-friendly APIs for Scala (its native language), Java, Python, and Spark SQL.Spark has an interactive mode so that developers and users can run queries.MapReduce has no interactive mode, but add-ons such as Hive and Pig  to make working with MapReduce a little easier for developers.
  6. Costs :Both MapReduce and Spark are Apache projects, which means that they’re open source and free software products. While there’s no cost for the software, there are costs associated with running either platform in personnel and in hardware. Both products are designed to run on commodity hardware, such as low cost, so-called white box server systems. However Spark systems cost more because of the large amounts of RAM required to run everything in memory. But what’s also true is that Spark’s technology reduces the number of required systems. So, you have significantly fewer systems that cost more. There’s probably a point at which Spark actually reduces costs per unit of computation even with the additional RAM requirement.
  7. API’s: Spark also includes its own graph computation library, GraphX. GraphX allows users to view the same data as graphs and as collections. Users can also transform and join graphs with Resilient Distributed Datasets (RDDs).
  8. Fault Tolerance: Hadoop uses Replicated blocks of data to maintain this feature. There is a link between TaskTrackers & JobTracker, so if its missed then the JobTracker reschedules all pending and in-progress operations to another TaskTracker. This effectively provides fault tolerance.Spark uses Resilient Distributed Datasets (RDDs), which are fault-tolerant collections of elements that can be operated on in parallel. RDDs can reference a dataset in an external storage system, such as a shared filesystem, HDFS, HBase, or any data source offering a Hadoop InputFormat. Spark can create RDDs from any storage source supported by Hadoop, including local filesystems or one of those listed previously.
  9. Scalability: both MapReduce and Spark are scalable using the HDFS.
  10. Security: Hadoop supports Kerberos authentication. HDFS supports access control lists (ACLs) and a traditional file permissions model. For user control in job submission, Hadoop provides Service Level Authorization, which ensures that clients have the right permissions.Spark’s security is a bit sparse by currently only supporting authentication via shared secret (password authentication). The security bonus that Spark can enjoy is that if you run Spark on HDFS, it can use HDFS ACLs and file-level permissions. Additionally, Spark can run on YARN giving it the capability of using Kerberos authentication.

Learn Spark Architecture by clicking here.

Hadoop Ecosystem Components contd…(Tutorial Day 5)

So continuing the old post, vendors that provide Hadoop-based platforms include Cloudera, Hortonworks, MapR, Greenplum, IBM, and Amazon. Here we will discuss more components of Hadoop ecosystem.

Data Access Components of Hadoop Ecosystem

  • Pig-

Apache Pig is a high-level platform for creating programs that run on Apache Hadoop. Apache Pig is a tool developed by Yahoo for analyzing huge data sets efficiently and easily. The high level data flow language for this platform is called Pig Latin. Pig can execute its Hadoop jobs in MapReduce, Apache Tez, or Apache Spark. The salient property of Pig programs is that their structure is amenable to substantial parallelization, which in turns enables them to handle very large data sets.

At the present time, Pig’s infrastructure layer consists of a compiler that produces sequences of Map-Reduce programs, for which large-scale parallel implementations already exist (e.g., the Hadoop subproject). Pig’s language layer currently consists of a textual language called Pig Latin.Pig is an open source project under the Apache Software Foundation, so you can learn about it online

Pig Latin is basically used it to construct dataflows, to have a scheduled job to periodically crunch the massive data from HDFS and transfer the summarized data into a relational database for reporting, & ad-hoc analyses. Hive is used for simple ad-hoc analytical queries for the data in HDFS, as Hive queries are a lot faster to write for those types of queries. Its generally used by Yahoo, Twitter etc to process web logs,images,maps etc.

Usage of Apache Pig:

  • Using Pig Latin, programmers can perform MapReduce tasks easily without having to type complex codes in Java, as it uses multi-query approach, thereby reducing the length of codes. For example, an operation that would require you to type 200 lines of code (LoC) in Java can be easily done by typing as less as just 10 LoC in Apache Pig. Ultimately Apache Pig reduces the development time by almost 16 times.
  • Pig Latin is SQL-like language and it is easy to learn Apache Pig when you are familiar with SQL.
  • Apache Pig provides many built-in operators to support data operations like joins, filters, ordering, etc. In addition, it also provides nested data types like tuples, bags, and maps that are missing from MapReduce.

Pig Use Case-

I am hereby using one of my fav use case of PIG Latin language, you can read here on Slideshare:

Scenario: You have a User data in one file ,website data in another. Now you want to find out the top 5 most visited pages by users of Age (18-25). For this scenario, MAp reduce program is full page length code, but in PIG Latin language its a small easily understandable code.

Code credit: Nick Dimiduk
  • Hive-

Hive is a Data warehouse system layer built on Hadoop. It allows to define a structure for unstructured big data and query the data using a SQL-like language called HiveQL. Its developed by Facebook & makes querying faster through indexing.

Hive Use Case-

Hive simplifies Hadoop at Facebook with the execution of 7500+ Hive jobs daily for Ad-hoc analysis, reporting and machine learning.


Read my next blog on more Hadoop ecosystem components (tutorial Day 6)

What are the difference between Hive / Impala & Pig

Comparing Impala to Hive & Pig

  • Queries expressed in high-level languages
  • Alternatives to writing map-reduce code
  • Used to analyze data stored on Hadoop cluster



It was created based on Google’s Dremel paper.
1) It is an interactive SQL like query engine that runs on top of Hadoop Distributed File System (HDFS).
2) Its an open source massively parallel processing (MPP) query engine on top of clustered systems like Apache Hadoop.
3) MPP style parallel databases have a relation model, more suitable for processing structured and semi-structured data. Due to its architectural advantages, it doesn’t involve the overheads of a MapReduce jobs viz. job setup and creation, slot assignment, split creation, map generation etc., hence enables low-latency.
4) It offers lower latency / processing time for the queries at the cost of less scalability and less stability.
5) Impala supports high-performance UDF (User Defined Function) written in C++, as well as reusing some Java-based Hive UDFs.
6) Impala does not return column overflows as NULL, so that customers can distinguish between NULL data and overflow conditions similar to how they do so with traditional database systems.
7) Impala does not store or interpret timestamps using the local timezone, to avoid undesired results from unexpected time zone issues. Timestamps are stored and interpreted relative to UTC.
8) Impala utilizes the Apache Sentry authorization framework for Security, which provides fine-grained role-based access control to protect data against unauthorized access or tampering.
9) It can query data stored in HDFS or HBase tables
10) Uses subset of SQL 92 and do not support Stored Procedure
11) The Impala TIMESTAMP type can represent dates ranging from 1400-01-01 to 9999-12-31.  
12) With Impala, you can query the following File formats:Parquet /Avro /RCFile /SequenceFile
 /Unstructured text
13)  Impala shares the meta store with Hive
14) Impala can process in milliseconds when running at low load conditions and Impala is one of the valid choices if no SQL parallel processing is executed.
15) Impala is an MPP-like engine, so each query you are executing on it will start executor on each and every node of your cluster. This delivers the best performance for a single query running on the cluster, but the total throughput degrades heavily under high concurrency. In such systems you should limit the amount of parallel queries to kinda low value of ~10.

Being highly used it still has cons like:

1)  Impala can’t handle complex data types(Array,Map or Struct)

2)  Impala is not fault tolerant For e.g. if you run a query in Impala and if the query fails you will have to start the query all over again
3) Doesnot not support Parameters in scripts

4) Impala does not currently support many of HiveQL statements like ,ANALYZE TABLE (the Impala equivalent is COMPUTE STATS),DESCRIBE COLUMN,DESCRIBE DATABASE,EXPORT TABLE,IMPORT TABLE, many more
5) Impala does not implicitly cast between string and numeric or Boolean types. Always use CAST() for these conversions.
6) Impala does perform implicit casts among the numeric types, when going from a smaller or less precise type to a larger or more precise one. For example, Impala will implicitly convert a SMALLINT to a BIGINT or FLOAT, but to convert from DOUBLE to FLOAT or INT to TINYINT requires a call to CAST() in the query.
7) Impala does perform implicit casts from string to timestamp. Impala has a restricted set of literal formats for the TIMESTAMP data type and the from_unixtime() format string.
8) Impala, is not currently supported by YARN 
9) Impala is not the best choice if there is a batch execution, and SQL parallel execution 


It is a component of Horton works Data Platform(HDP). 
1) Hive provides a SQL-like interface to data stored in Hadoop clusters. 
2) It translate SQL queries into MapReduce/Tez/Spark jobs and executes them on the cluster, to implement batch based processing. Hence best suited for ETL- long running queries.
3) Its used by Data Analyst for completely structured data.
4) Supports complex Data types like arrays, Struct etc, custom file formats, “DATE” data type,XML and JSON functions.
5) Its fault tolerant .For e.g. if you run a query in hive mapreduce and while the query is running one of your data-node goes down still the output is given as  query will start running mapreduce jobs in other nodes.Its fault tolerant.
6) Supports Parameters Which Can Come Handy While Writing Hive Scripts.
7)  Its supported by YARN. So you can manage your resources for mapreduce or any other applications supported by YARN
8) Hive runs on top of MapReduce/Tez framework which requests resources based on the amount of data to process. This way for large clusters it would give you much better concurrency for “small” queries, as each of them would request small amount of execution resources which would result in more queries running in parallel.
9) The Hive component included in CDH 5.1 and higher now includes Sentry-enabled security .GRANT, REVOKE, and CREATE/DROP ROLE statements. Earlier Hive releases had a privilege system with GRANT and REVOKE statements that were primarily intended to prevent accidental deletion of data, rather than a security mechanism to protect against malicious users.
10) Uses subset of SQL 92 and do not support Stored Procedure
11) Hive TIMESTAMP type can represent dates ranging from 0000-01-01 to 9999-12-31. 
12) Hive supports several file formats like Text File /SequenceFile /RCFile/ Avro Files/ORC Files
     / Parquet/ Custom INPUTFORMAT and OUTPUTFORMAT. 

But the cons are big as well – 

1) Since Hive uses MapReduce to access Hadoop clusters, query overheads results in high latency. 
2) lower performance especially for table joins
3) No query optimizer 


Pig which is a scripting language with a focus on data flows.It has two parts:
a) A language for processing data, called Pig Latin.

b) A set of evaluation mechanisms for evaluating a Pig Latin program. Current evaluation mechanisms include (a) local evaluation in a single JVM, (b) evaluation by translation into one or more Map-Reduce jobs, executed using Hadoop

1) Pig can process data of any format, such as tab delimited text files, are supported via built-in capabilities. A user can add support for a file format by writing a function that parses the bytes of a file into objects in Pig’s data model, and vice versa.
2) Pig’s data model is similar to the relational data model.
3) In Pig, tables are called bags. Pig also has a “map” data type, which is useful in representing semi-structured data, e.g. JSON or XML.
4)  It can combine multiple data sets, via operations such as join, union or co-group, OR can split a single data set into multiple ones, using an operation called split.
5) It is a Procedural Data Flow Language and mostly used by Researchers or programmers.
6) Pig is Fault Tolerant
7) Pig supports “maps” of (key, value) pairs, where retrieving the value associated with a given key is an efficient operation. Maps provide a convenient way to represent semi-structured data, where the set of non-null fields varies from record to record. Maps are helpful when processing JSON, XML, and sparse relational data (i.e., tables with a lot of null values).