Hortonworks HDPCD Exam Practice Test Instant Access

Question 1

Which HDFS command copies an HDFS file named foo to the local filesystem as localFoo?

Ahadoop fs -get foo LocalFoo

Bhadoop -cp foo LocalFoo

Chadoop fs -Is foo

Dhadoop fs -put foo LocalFoo

Answer : A

Question 2

When can a reduce class also serve as a combiner without affecting the output of a MapReduce program?

AWhen the types of the reduce operation's input key and input value match the types of the reducer's output key and output value and when the reduce operation is both communicative and associative.

BWhen the signature of the reduce method matches the signature of the combine method.

CAlways. Code can be reused in Java since it is a polymorphic object-oriented programming language.

DAlways. The point of a combiner is to serve as a mini-reducer directly after the map phase to increase performance.

ENever. Combiners and reducers must be implemented separately because they serve different purposes.

Answer : A

You can use your reducer code as a combiner if the operation performed is commutative and associative.

Question 3

Which best describes what the map method accepts and emits?

AIt accepts a single key-value pair as input and emits a single key and list of corresponding values as output.

BIt accepts a single key-value pairs as input and can emit only one key-value pair as output.

CIt accepts a list key-value pairs as input and can emit only one key-value pair as output.

DIt accepts a single key-value pairs as input and can emit any number of key-value pair as output, including zero.

Answer : D

public class Mapper<KEYIN,VALUEIN,KEYOUT,VALUEOUT>

extends Object

Maps input key/value pairs to a set of intermediate key/value pairs.

Maps are the individual tasks which transform input records into a intermediate records. The transformed intermediate records need not be of the same type as the input records. A given input pair may map to zero or many output pairs.

Class Mapper<KEYIN,VALUEIN,KEYOUT,VALUEOUT>

Question 4

Workflows expressed in Oozie can contain:

ASequences of MapReduce and Pig. These sequences can be combined with other actions including forks, decision points, and path joins.

BSequences of MapReduce job only; on Pig on Hive tasks or jobs. These MapReduce sequences can be combined with forks and path joins.

CSequences of MapReduce and Pig jobs. These are limited to linear sequences of actions with exception handlers but no forks.

DIterntive repetition of MapReduce jobs until a desired answer or state is reached.

Answer : A

Oozie workflow is a collection of actions (i.e. Hadoop Map/Reduce jobs, Pig jobs) arranged in a control dependency DAG (Direct Acyclic Graph), specifying a sequence of actions execution. This graph is specified in hPDL (a XML Process Definition Language).

hPDL is a fairly compact language, using a limited amount of flow control and action nodes. Control nodes define the flow of execution and include beginning and end of a workflow (start, end and fail nodes) and mechanisms to control the workflow execution path ( decision, fork and join nodes).

Workflow definitions

Currently running workflow instances, including instance states and variables

Note: Oozie is a Java Web-Application that runs in a Java servlet-container - Tomcat and uses a database to store:

Question 5

You need to move a file titled ''weblogs'' into HDFS. When you try to copy the file, you can't. You know you have ample space on your DataNodes. Which action should you take to relieve this situation and store more files in HDFS?

AIncrease the block size on all current files in HDFS.

BIncrease the block size on your remaining files.

CDecrease the block size on your remaining files.

DIncrease the amount of memory for the NameNode.

EIncrease the number of disks (or size) for the NameNode.

FDecrease the block size on all current files in HDFS.

Answer : C

Question 6

A client application creates an HDFS file named foo.txt with a replication factor of 3. Identify which best describes the file access rules in HDFS if the file has a single block that is stored on data nodes A, B and C?

AThe file will be marked as corrupted if data node B fails during the creation of the file.

BEach data node locks the local file to prohibit concurrent readers and writers of the file.

CEach data node stores a copy of the file in the local file system with the same name as the HDFS file.

DThe file can be accessed if at least one of the data nodes storing the file is available.

Answer : D

HDFS keeps three copies of a block on three different datanodes to protect against truedata corruption. HDFS also tries to distribute these three replicas on more than one rack to protect againstdata availabilityissues. The fact that HDFS actively monitors any failed datanode(s) and upon failure detection immediately schedules re-replication of blocks (if needed) implies that three copies of data on three different nodes is sufficient to avoid corrupted files.

Note:

HDFS is designed to reliably store very large files across machines in a large cluster. It stores each file as a sequence of blocks; all blocks in a file except the last block are the same size. The blocks of a file are replicated for fault tolerance. The block size and replication factor are configurable per file. An application can specify the number of replicas of a file. The replication factor can be specified at file creation time and can be changed later. Files in HDFS are write-once and have strictly one writer at any time. The NameNode makes all decisions regarding replication of blocks. HDFS uses rack-aware replica placement policy. In default configuration there are total 3 copies of a datablock on HDFS, 2 copies are stored on datanodes on same rack and 3rd copy on a different rack.

Question 7

Indentify which best defines a SequenceFile?

AA SequenceFile contains a binary encoding of an arbitrary number of homogeneous Writable objects

BA SequenceFile contains a binary encoding of an arbitrary number of heterogeneous Writable objects

CA SequenceFile contains a binary encoding of an arbitrary number of WritableComparable objects, in sorted order.

DA SequenceFile contains a binary encoding of an arbitrary number key-value pairs. Each key must be the same type. Each value must be the same type.

Answer : D

SequenceFile is a flat file consisting of binary key/value pairs.

There are 3 different SequenceFile formats:

Uncompressed key/value records.

Record compressed key/value records - only 'values' are compressed here.

Block compressed key/value records - both keys and values are collected in 'blocks' separately and compressed. The size of the 'block' is configurable.

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