Apache Cassandra Interview Questions and Answers | Cassandra Tutorial | Cassandra Training | Edureka

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Agenda
❖ Cassandra Salary Trend
❖ Cassandra History and it’s Users in Market
❖ Performance Comparison
❖ General NoSQL Questions
❖ Cassandra Beginners Questions
❖ Cassandra Advance Questions

Cassandra Salary Trend
₹ 700 K
₹ 1.4 M
₹ 2.1 M
₹ 413,000
₹ 909,694
₹ 1,922,300
Years Experience1-4 years 5-9 years >10 years
Source : Payscale

Cassandra Users in Market

Cassandra History
Cassandra was
developed at
Facebook for inbox
search
Open-sourced by
Facebook in July
2008
Accepted into
Apache Incubator in
March 2009
Top level Apache
project since
February 2010
Influenced by
“Google BigTable”
and “Amazon
Dynamo”

Performance : Various NoSQL DBMS

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General
NoSQL
Cassandra
Beginners
Cassandra
Advanced

NoSQL General Questions
What is a NoSQL Database?
1
• NoSQL is also referred as Not only SQL to emphasize that they may support SQL-like query language used
in relational database.
• NoSQL database provides a mechanism to store and retrieve data, which are modeled rather than the tabular
relations used in Relational databases.
A

What are the key features of any NoSQL Database?
2

What are the different types of NoSQL Databases?
3
Key Value Store01
Document Store02
Column Store03
Graph Database04

What is Key Value Store DB? Explain with an example.
4
• All of the data within database consists of an indexed key and a value.
• A key may correspond to one or multiple values (hash table).
• Gives great performance and can be very easily scaled as per business needs.

What is Document Store DB? Explain with an example.
5
• Data record is the JSON/XML representation of key-value pairs.
• Every record can have different set of fields.
• Document DBs are similar to Key-value pairs
• But the difference is that the key is associated with a document

What is Column Store DB? Explain with an example.
6
• Data is stored in cells are grouped in columns of data rather than as rows of data.
• Columns are logically grouped into column families.
• One row may have one or multiple data records, which is indexed by a partition key.

What is Graph DB? Explain with an example.
7
• A flexible graphical representation is used.
• Key purpose is to store relationships between nodes.
• Here, Nodes are Id 1, 2 and 3. Properties for Node 1 are Name and Age
• Edges are : Id 100, 101, 102, 103, 104 and 105

Cassandra Beginners Questions
What is Apache Cassandra?
1
• Apache Cassandra is a free and open-source distributed NoSQL database management
system designed to handle large amounts of data across many commodity servers,
providing high availability with no single point of failure.
A

What are the features of Apache Cassandra?
2

What are the Different types of Data Model?
3
• Conceptual Data Model
• Logical Data Model
• Physical Data Model
A

What are the Key Differences between Cassandra and Traditional RDBMS?
4

What are the different Database Elements of Cassandra?
5

What is CQLSH? And why is it used?
6
• Cassandra-Cqlsh is a query language that enables users to communicate with its database.
By using Cassandra cqlsh, you can do following things:
• Define a schema
• Insert a data, and
• Execute a query
A

What is a YAML file in Cassandra?
7
• The cassandra.yaml file is the main configuration file for Cassandra.
• After changing properties in the cassandra.yaml file, you must restart the node for the
changes to take effect.
A

What are Clusters in Cassandra?
8
• The outermost structure in Cassandra is the cluster
• Cluster is a container for Keyspaces
• Sometimes called the ring, because Cassandra assigns data to nodes in the cluster by
arranging them in a ring
• A node holds a replica for different range of data
A

What is a Keyspace in Cassandra?
9
• A keyspace is the outermost container for data in Cassandra
• Like a relational database, a keyspace has a name and a set of attributes that define
keyspace-wide behaviour
• Keyspace is used to group Column Families together
A

How is a Keyspace created in Cassandra? & What are the parameters used?
10
A

What are durable writes?
11
• Provides a means to instruct Cassandra whether to use commitlog for updates on the
current KeySpace or not.
• This option is not mandatory.
• Default value for durable writes is TRUE.
A

What are the steps to Describe, USE and Delete the Keyspaces?
12

What do you mean by replication factor?
13
• Cassandra stores copies (called replicas) of each row based on the row key
• The replication factor refers to the number of nodes that will act as copies (replicas) of each
row of data
A

What do you mean by replication Strategy?
14
• The replica placement strategy refers to how the replicas will be placed in the ring
• There are different strategies that ship with Cassandra for determining which nodes will get
copies of which keys
• There are mainly two types of Strategies:
• Simple Strategy
• Network Topology Strategy
A

What is Simple Strategy?
15
• It uses Simple Single Datacenter Clusters
• It places the first Replica on a node determined by the Partitioner
• Additional Replicas are placed on the next nodes in clockwise (in a Ring) manner without
considering Rack or Datacenter location
A

What is Network Topology Strategy?
16
• This is used when we deploy a cluster across Multiple Datacenters
• Primary consideration to insert replicas
• Can satisfy reads, locally without incurring cross Data-Center Latency
• Handling Failure Scenarios
A

What is a Column Family?
17
• A column family is a container for an ordered collection of rows, each of which is itself an
ordered collection of columns
• We can freely add any column to any column family at any time, depending on your needs
• The comparator value indicates how columns will be sorted when they are returned to you
in a query
A

What is a Column Family?
17

What is a Row in Cassandra? and What are the different elements of it?
18
• Row is a collection of sorted columns
• It is the smallest unit that stores related data in Cassandra
• Any component of a Row can store data or metadata
A

What is a Primary Key? And what are it’s different types?
19
• The Primary Key is a column that is used to uniquely identify a row
A

Differentiate between the various types of Primary Keys in Cassandra.
20

Differentiate between Static and Dynamic CQL Tables
21
• A Static Table uses a relatively static set of column names and is similar to Relational
Database Table
• A dynamic table allows you to pre-compute result sets and store them in a single row for
efficient data retrieval
A

Differentiate between Drop and Truncate in CQLSH
22
• The Drop table command drops specified table including all the data from the keyspace.
• The Truncate table command is used to truncate a table and deletes all the rows of the table
permanently.
A

Cassandra Advance Questions
What is Gossip Protocol ?
1
• Gossip Protocol in Cassandra is a peer-to-peer communication protocol in which nodes can
choose among themselves with whom they want to exchange their state information.
A

How does gossip Protocol Work?
2

How does gossip Protocol help in Failure Detection?
3

What are partitions and Tokens in Cassandra?
4
• Partition: It is a hash function located on each node which hashes tokens from designated
values in rows being added
• It converts a variable length input to a fixed length value.
A
• Token: Integer value generated by a hashing algorithm, identifying a partition's location
within a cluster
A

What are partitions and Tokens in Cassandra?
4

What are the different types of Partitioners in Cassandra? Explain.
5

What do you mean by Snitch? Name a few.
6
• A snitch determines which datacenters and racks, nodes belong to.
• They inform Cassandra about the network topology and allows Cassandra to distribute
replicas
• Specifically, the Replication strategy places the replicas based on the information provided
by the new snitch
A

How does Cassandra perform write operations?
6

Explain the terms Memtable, CommitLog and SSTables.
7

What is the use of Coordinator Node in Read?
8
• Read Operation is easy, because clients can connect to any node in the cluster to perform
reads
• If a client connects to a node that doesn’t have the data it’s trying to read, the node it’s
connected to will act as coordinator node
A

How does Cassandra perform Read operation? Explain
9

What do you mean by Compaction?
10
• It is the process of freeing up space by merging large accumulated datafiles
A

What is Anti-Entropy and How is it associated to Merkel Tree?
11
• Anti-entropy is the replica synchronization mechanism, ensuring that data on different nodes
is updated to the newest version
• Cassandra uses Merkle tree for anti-entropy repair
• Merkel Tree is a hash tree where leaves are hashes of the values of individual keys
A

Explain the different types of Repairs.
12

What is Hinted Handoff?
13
• Hinted Handoff is a mechanism to ensure availability, fault-tolerance and graceful
degradation in Cassandra
• The node that receives the hint will know when the unavailable node comes back online
again, because of Gossip
A

What is Hinted Handoff?
14
• Hinted Handoff is a mechanism to ensure availability, fault-tolerance and graceful
degradation in Cassandra
• The node that receives the hint will know when the unavailable node comes back online
again, because of Gossip
A

What are Roles in CQLSH?
15
• Roles enable authorization management on a larger scale than security per user can provide
A

What do you mean by Logging in Cassandra? Mention a few levels of Logging
16
• Logs are written to the system.log and debug.log file in the Cassandra logging directory
• We can configure logging programmatically or manually
• The simplest way to get a picture of what’s happening in your database is to just change the
logging level to make the output more verbose, by default it is set at INFO.
A

How can one change the Logging Level in Cassandra and Why ?
17
• By default, the Cassandra server log level is set at INFO
• INFO doesn’t give much detail about the work Cassandra is doing, it just outputs basic status
updates
• By changing the logging level to DEBUG, we can see much more clearly what activity the
server is working on
A

What is JMX? And How is it useful in Cassandra?
18
• JMX (Java Management Extension) is a Java technology that supplies tools for managing and
monitoring Java applications and services
• Cassandra makes use of JMX to enable remote management of the servers
A

Explain Nodetool Utility.
19
• The Nodetool Utility is a command-line utility that comes out of the box with Cassandra and
is a great tool for administration and monitoring.
• It communicates with JMX to perform operational and monitoring tasks exposed by MBeans
A

Explain Nodetool Utility tools and how to use them?
20

What are snapshots and how do you create one in Cassandra?
21
• Snapshot represents the state of the data files at a particular point in time
• Snapshot command is used while taking a backup and creates hard links for SSTables in the
snapshots folder which can later be used to restore the node
A

Why is JConsole used? What are it’s different elements?
22
• JConsole is used to Monitor and perform analysis on the Server activities.
• Once you’ve connected to a server, the default view includes four major categories about
your server’s state, which are updated constantly:
A

What is Python Stress test in Cassandra?
23
• Cassandra comes with a popular utility called py_stress that can be used to run a stress test
on Cassandra cluster.
• The cassandra-stress tool is a Java-based stress testing utility for basic benchmarking and
load testing a Cassandra cluster.
• This is an effective tool for populating a cluster and stress testing CQL tables and queries
A

Apache Cassandra Interview Questions and Answers | Cassandra Tutorial | Cassandra Training | Edureka

Apache Cassandra Interview Questions and Answers | Cassandra Tutorial | Cassandra Training | Edureka

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