CHAPTER 1 Flashcards by Besnik Emini

What does NoSQL stand for?

Not Only SQL

Refers to a set of modern databases that do not use traditional relational models.

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What is a key trait of NoSQL databases?

Schema-less

Data can be stored as key-value pairs, documents, columns, or graphs.

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Why are NoSQL databases needed?

Traditional SQL databases can’t scale for volume, variety, and velocity of modern data.

Examples include social media, IoT, and e-commerce.

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What are the 7 V’s of Big Data?

Volume
Velocity
Variety
Variability
Veracity
Visualization
Value

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Who defined relational databases (RDBMS) and when?

Edgar Codd in 1970.

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What are the ACID properties in RDBMS?

Atomicity
Consistency
Isolation
Durability

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What is a limitation of RDBMS?

Fixed schemas, hard to scale horizontally, not suitable for massive or semi-structured data.

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What are the main characteristics of NoSQL?

Horizontal Scalability
Schema-less
High Performance
Open-source and cost-effective
Eventual Consistency

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What are the challenges of NoSQL?

Immature technology
Lack of standards
Limited professional support
Complex administration
Fewer experts compared to SQL

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What is a Key-Value Store?

The simplest form of a NoSQL database, storing data as (key, value) pairs.

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Name an example of a Key-Value Store.

Redis, Amazon DynamoDB, Voldemort.

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What are the basic operations of a Key-Value Store?

put(key, value)
get(key)
delete(key)

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When is it appropriate to use Key-Value Stores?

For storing data accessed only by key, such as session data, user profiles, and shopping cart data.

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When should you avoid using Key-Value Stores?

Need for relationships between data
Require multi-key transactions
Need queries based on values
Need batch operations

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What is Redis?

An open-source, in-memory, key-value store.

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What are some key features of Redis?

Data types: strings, lists, sets, sorted sets, hashes
Atomic operations
Persistence options
Pub/Sub messaging

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What is the CAP Theorem?

Consistency, Availability, Partition Tolerance. You can’t have all three in a distributed system.

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What does the BASE model stand for?

Basically Available
Soft state
Eventual consistency

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What is the difference between vertical and horizontal scaling?

Vertical Scaling: Add more power to a single machine
Horizontal Scaling: Add more machines

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What is sharding in NoSQL?

Data partitioning across multiple machines based on a key.

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What is eventual consistency in NoSQL?

Data updates are not always immediately visible across all nodes but will eventually become consistent.

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What is MapReduce?

A programming model for processing large datasets across many machines.

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What are the phases of MapReduce?

Map Phase
Shuffle Phase
Reduce Phase

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What is a combiner in MapReduce?

An optional optimization that aggregates data locally before shuffling.

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What does HDFS stand for?

Hadoop Distributed File System.

What is the role of the NameNode in HDFS?

Manages metadata such as file locations and directory structure.

What happens if a DataNode doesn’t send a Heartbeat?

It is considered dead, and the NameNode replicates blocks from dead nodes.

What is the purpose of the JobTracker in Hadoop?

Coordinates the job execution.

What is the main use case for MapReduce?

Batch processing of large datasets.

What are some characteristics of MapReduce?

* Shared nothing architecture * Highly parallel and fault-tolerant * Not suitable for real-time processing

What is an aggregate in NoSQL?

A group of logically related data processed as a unit.

What is the primary feature of Redis regarding data storage?

In-memory data storage ## Footnote Data is stored in RAM, making reads and writes extremely fast.

What happens if Redis runs out of memory?

It can be killed by OS, crash, or slow down ## Footnote Monitoring with INFO command is recommended.

What is the maximum length of a Redis String?

512 MB

Which commands are used with Redis Strings?

* GET * SET * APPEND * INCR * DECR * STRLEN

What is a List in Redis?

An ordered collection of strings

Which commands are used with Redis Lists?

* LPUSH * RPUSH * LPOP * RPOP * LRANGE * LLEN

What defines a Set in Redis?

An unordered collection of unique strings

Which commands are used with Redis Sets?

* SADD * SREM * SINTER * SUNION * SISMEMBER

What is a Sorted Set in Redis?

Each element has a score to keep them sorted

Which commands are used with Redis Sorted Sets?

* ZADD * ZINCRBY * ZRANGE * ZCOUNT * ZREM

What does a Hash in Redis resemble?

Like a row in a relational table (fields and values)

Which commands are used with Redis Hashes?

* HSET * HGET * HGETALL * HDEL * HINCRBY

How are transactions handled in Redis?

Commands are queued using MULTI and executed with EXEC

What is the behavior of Redis transactions if one command fails?

Other commands still run

What is the role of Redis Master-Slave Replication?

One master handles writes, slaves copy data and handle reads

What happens if a slave disconnects in Redis Replication?

It reconnects automatically

What is Redis Sentinel used for?

Ensures high availability and performs automatic failover

What is the purpose of Redis Partitioning?

Splitting data across multiple Redis servers

What are the two types of partitioning in Redis?

* Range Partitioning * Hash Partitioning

What are the two methods of persistence in Redis?

* RDB (Snapshot) * AOF (Append-Only File)

What command makes a snapshot in Redis?

SAVE

What is the CAP Theorem in relation to Redis?

Redis cannot have Consistency, Availability, and Partition Tolerance all at the same time

Which feature does Redis favor according to the CAP theorem?

Availability + Performance over strict Consistency

What is the command to set a key with an expiration in Redis?

EXPIRE

What is the command to retrieve a key in Redis?

GET

What is the structure of a Map function in MapReduce?

function map(text): for each word in text: emit(word, 1)

What is the structure of a Reduce function in MapReduce?

function reduce(word, counts): total = sum(counts); emit(word, total)

How do you add an item to a Redis List?

Using LPUSH or RPUSH commands

What command retrieves all items in a Redis List?

LRANGE

What command removes the last item from a Redis List?

RPOP

What command is used to increase a score in a Redis Sorted Set?

ZINCRBY

What command counts items in a Redis Sorted Set within a specific range?

ZCOUNT

What command displays items in a Redis Sorted Set within a score range?

ZRANGEBYSCORE

What command is used to store product inventory using hashes in Redis?

HSET

What command reduces quantity by 1 when a product is sold in Redis?

HINCRBY