Key-Value Stores in Databases

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Questions and Answers

What is a key-value store, also referred to as?

object-oriented database

non-relational database (correct)

graph database

relational database

What is a requirement for a key in a key-value pair?

it must be unique (correct)

it must be a string

it can be null

it can be duplicated

What is the purpose of using a short key in a key-value store?

for better performance (correct)

for better data compression

for faster data retrieval

for better security

What type of data can a value in a key-value pair be?

strings, lists, objects, etc. Signup and view all the answers

What is the purpose of the put operation in a key-value store?

to insert a value associated with a key Signup and view all the answers

What is a characteristic of the key-value store designed in this chapter?

high availability and tunable consistency Signup and view all the answers

What is an advantage of using a hash table to store key-value pairs in a single server key-value store?

it keeps everything in memory Signup and view all the answers

What is a tradeoff that must be made when designing a key-value store?

between consistency and availability Signup and view all the answers

What is a major limitation of memory access?

It may not fit everything due to space constraints Signup and view all the answers

What is a common technique used to fit more data in a single server?

Data compression Signup and view all the answers

What is another name for a distributed key-value store?

Distributed hash table Signup and view all the answers

What does the CAP theorem state?

It is impossible for a distributed system to provide all three guarantees: consistency, availability, and partition tolerance Signup and view all the answers

What does consistency mean in the context of the CAP theorem?

All clients see the same data at the same time, no matter which node they connect to Signup and view all the answers

What is an AP key-value store?

A key-value store that supports availability and partition tolerance Signup and view all the answers

What is a partition in the context of the CAP theorem?

A communication break between two nodes Signup and view all the answers

What is a CA key-value store?

A key-value store that supports consistency and availability Signup and view all the answers

Study Notes

Key-Value Stores

A key-value store is a non-relational database that stores unique identifiers as keys with their associated values.
Each key-value pair consists of a unique key and a value that can be accessed through the key.
Keys can be plain text or hashed values, and shorter keys are preferred for performance reasons.

Key-Value Pair Examples

Plain text key: “last_logged_in_at”
Hashed key: 253DDEC4
Values can be strings, lists, objects, etc.

Key-Value Store Operations

put(key, value): inserts “value” associated with “key”
get(key): gets “value” associated with “key”

Design Requirements

Small key-value pair size: less than 10 KB
Ability to store big data
High availability: system responds quickly, even during failures
High scalability: system can be scaled to support large data sets
Automatic scaling: addition/deletion of servers should be automatic based on traffic
Tunable consistency
Low latency

Single Server Key-Value Store

Storing key-value pairs in a hash table, keeping everything in memory
Optimizations:
- Data compression
- Store only frequently used data in memory and the rest on disk

Distributed Key-Value Store

Also called a distributed hash table, distributing key-value pairs across many servers
CAP theorem: it is impossible for a distributed system to simultaneously provide more than two of the three guarantees: consistency, availability, and partition tolerance

CAP Theorem Definitions

Consistency: all clients see the same data at the same time no matter which node they connect to
Availability: any client which requests data gets a response even if some of the nodes are down
Partition Tolerance: system continues to operate despite network partitions

CAP Theorem Classification

CP (consistency and partition tolerance) systems: sacrifice availability
AP (availability and partition tolerance) systems: sacrifice consistency
CA (consistency and availability) systems: sacrifice partition tolerance

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Description

Learn about key-value stores, a type of non-relational database that uses unique identifiers as keys to access associated values. Understand the properties of keys and values in this data pairing.