News feed generation in HLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the main component responsible for storing user posts in a news feed system.

HLD

The component that stores all user posts is called the [1].

Drag options to blanks, or click blank then click option'

AFeed Generator

BNotification Service

CPost Database

DCache Layer

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing the feed generator with the storage component.

Choosing cache layer which is temporary storage.

The Post Database stores all user posts which are later fetched to generate the news feed.

2fill in blank

medium

Complete the code to specify the process that combines posts from followed users to create a personalized feed.

HLD

The process that combines posts from followed users is called the [1].

Drag options to blanks, or click blank then click option'

APost Indexing

BFeed Aggregation

CUser Authentication

DContent Moderation

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing post indexing which is about organizing posts.

Confusing with user authentication which is login related.

Feed Aggregation collects posts from all followed users to build the personalized news feed.

3fill in blank

hard

Fix the error in the description of the caching layer used to speed up feed retrieval.

HLD

The caching layer stores [1] copies of the news feed to reduce database load.

Drag options to blanks, or click blank then click option'

Atemporary

Bpermanent

Cencrypted

Darchived

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing permanent which defeats the purpose of cache.

Confusing with encrypted or archived which are unrelated here.

The caching layer stores temporary copies to quickly serve feeds without hitting the database every time.

4fill in blank

hard

Fill both blanks to complete the description of feed generation methods.

HLD

In [1] feed generation, posts are combined in real-time, while in [2] feed generation, feeds are precomputed and stored.

Drag options to blanks, or click blank then click option'

APull-based

BPush-based

CBatch

DStream

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing batch and stream which are data processing terms.

Confusing push and pull methods.

Pull-based feed generation fetches posts when requested (real-time). Push-based precomputes feeds and pushes them to users.

5fill in blank

hard

Fill all three blanks to complete the description of components in a scalable news feed system.

HLD

The [1] handles user requests, the [2] stores posts, and the [3] speeds up feed retrieval by caching.

Drag options to blanks, or click blank then click option'

AAPI Gateway

BPost Database

CCache Layer

DLoad Balancer

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing Load Balancer with API Gateway.

Mixing up Cache Layer and Post Database roles.

The API Gateway manages user requests, the Post Database stores posts, and the Cache Layer speeds up retrieval.

Practice

1. What is the main purpose of a news feed generation system in social media platforms?

easy

A. To store user passwords securely

B. To manage user account settings

C. To show personalized and timely content to users

D. To handle payment transactions

Solution

1. Step 1: Understand the role of news feed generation

   The news feed system is designed to deliver content that is relevant and timely to each user.

2. Step 2: Identify the correct purpose among options

   The other options relate to security, settings, and payments, which are unrelated to news feed generation.

3. Final Answer:

   To show personalized and timely content to users -> Option C

4. Quick Check:

   News feed = personalized timely content [OK]

Hint: News feed = personalized content display [OK]

Common Mistakes:

• Confusing news feed with user authentication
• Mixing news feed with payment processing
• Thinking news feed manages account settings

2. Which of the following is a common method used in news feed generation to deliver updates efficiently?

easy

A. Manual refresh by users only

B. Push model where updates are sent to users proactively

C. Storing all data in a single database without caching

D. Using FTP to transfer news feed data

Solution

1. Step 1: Identify common delivery methods in news feed systems

   Push model proactively sends updates to users, improving latency and experience.

2. Step 2: Evaluate other options for efficiency

   Manual refresh is user-driven and less efficient; no caching slows performance; FTP is unrelated to real-time feed delivery.

3. Final Answer:

   Push model where updates are sent to users proactively -> Option B

4. Quick Check:

   Push model = efficient update delivery [OK]

Hint: Push model proactively sends updates [OK]

Common Mistakes:

• Assuming manual refresh is efficient
• Ignoring caching benefits
• Confusing FTP with real-time data delivery

3. Consider a news feed system using a pull model where users request their feed on demand. What is a likely outcome when many users request feeds simultaneously?

medium

A. Users receive outdated feeds only

B. Instant delivery with no server load

C. System automatically caches all feeds without delay

D. High latency and increased load on backend servers

Solution

1. Step 1: Understand pull model behavior under load

   Pull model requires backend to generate feeds on request, causing high load if many users request simultaneously.

2. Step 2: Analyze other options for feasibility

   Instant delivery with no load is unrealistic; outdated feeds depend on caching, not pull model alone; automatic caching without delay is ideal but not guaranteed.

3. Final Answer:

   High latency and increased load on backend servers -> Option D

4. Quick Check:

   Pull model + many requests = high load [OK]

Hint: Pull model causes backend load spikes [OK]

Common Mistakes:

• Assuming pull model has no latency
• Confusing caching with pull model behavior
• Believing feeds are always instantly cached

4. A news feed system uses a push model but users report seeing stale content. Which is the most likely cause?

medium

A. Cache not invalidated after new content is pushed

B. Users are not refreshing their browsers

C. Backend servers are down

D. Users have slow internet connections

Solution

1. Step 1: Identify push model behavior and caching role

   Push model sends updates, but if cache is not invalidated, users see old content.

2. Step 2: Evaluate other options for staleness cause

   Browser refresh is less relevant in push; backend down causes no updates; slow internet delays but does not cause stale cached data.

3. Final Answer:

   Cache not invalidated after new content is pushed -> Option A

4. Quick Check:

   Push + stale feed = cache invalidation issue [OK]

Hint: Stale feed often means cache invalidation failed [OK]

Common Mistakes:

• Blaming user refresh instead of cache
• Ignoring cache invalidation importance
• Assuming slow internet causes stale cache

5. You are designing a news feed system for a platform with 100 million users. Which approach best balances scalability and freshness of content?

hard

A. Hybrid model: push important updates and pull less critical content

B. Pure pull model: generate feed on every user request

C. Pure push model: push all updates to all users immediately

D. No caching: always fetch fresh data from database

Solution

1. Step 1: Analyze scalability and freshness needs for large user base

   Pure pull causes high load; pure push is costly and complex; no caching is inefficient.

2. Step 2: Evaluate hybrid model benefits

   Hybrid model pushes critical updates for freshness and uses pull for less urgent content, balancing load and latency.

3. Final Answer:

   Hybrid model: push important updates and pull less critical content -> Option A

4. Quick Check:

   Hybrid model balances scale and freshness [OK]

Hint: Hybrid push-pull balances scale and freshness [OK]

Common Mistakes:

• Choosing pure pull causing backend overload
• Choosing pure push causing network overload
• Ignoring caching and load balancing