Why webhooks push notifications in Rest API - Performance Analysis

Time Complexity: Why webhooks push notifications

O(n)

Understanding Time Complexity

When webhooks push notifications, they send data automatically to another system. We want to understand how the time it takes grows as more notifications are sent.

How does the work increase when the number of notifications grows?

Scenario Under Consideration

Analyze the time complexity of the following webhook notification process.

POST /webhook/notify
for each subscriber in subscribers_list:
  send HTTP POST notification
  wait for response
return success
    

This code sends a notification to each subscriber one by one and waits for their response.

Identify Repeating Operations

Look for repeated actions that take time.

• Primary operation: Sending HTTP POST notification to each subscriber.
• How many times: Once for every subscriber in the list.

How Execution Grows With Input

As the number of subscribers grows, the number of notifications sent grows the same way.

Input Size (n)	Approx. Operations
10	10 notifications sent
100	100 notifications sent
1000	1000 notifications sent

Pattern observation: The work grows directly with the number of subscribers.

Final Time Complexity

Time Complexity: O(n)

This means the time to send notifications grows in a straight line with the number of subscribers.

Common Mistake

[X] Wrong: "Sending notifications happens instantly no matter how many subscribers there are."

[OK] Correct: Each notification takes time, so more subscribers mean more total time.

Interview Connect

Understanding how notification sending scales helps you explain real-world API behavior clearly and confidently.

Self-Check

"What if notifications were sent in parallel instead of one by one? How would the time complexity change?"

Practice

1. Why do webhooks push notifications instead of waiting for your app to ask for updates?

easy

A. To avoid sending any data to your app

B. To send updates instantly and save time and resources

C. To require your app to check for updates repeatedly

D. To make your app slower by adding delays

Solution

1. Step 1: Understand the purpose of webhooks

   Webhooks are designed to send data immediately when an event happens, instead of waiting for your app to ask.

2. Step 2: Compare push vs pull methods

   Push (webhooks) saves time and resources by sending updates instantly, unlike pull which requires repeated checking.

3. Final Answer:

   To send updates instantly and save time and resources -> Option B

4. Quick Check:

   Push notifications = instant updates [OK]

Hint: Webhooks push to save time and avoid repeated checks [OK]

Common Mistakes:

• Thinking webhooks slow down the app
• Confusing push with pull methods
• Believing webhooks avoid sending data

2. Which HTTP method do webhooks commonly use to send notifications?

easy

A. POST

B. DELETE

C. GET

D. PUT

Solution

1. Step 1: Identify the HTTP method for sending data

   Webhooks send event data to your app, which requires a method that can carry data in the request body.

2. Step 2: Match HTTP methods to their purpose

   POST is used to send data to a server, unlike GET which only requests data without sending a body.

3. Final Answer:

   POST -> Option A

4. Quick Check:

   Webhooks use POST to send data [OK]

Hint: Webhooks send data using POST requests [OK]

Common Mistakes:

• Choosing GET which only retrieves data
• Confusing PUT or DELETE with sending notifications
• Not knowing HTTP methods' purposes

3. Consider this webhook setup: Your app receives a POST request with event data immediately when a user updates their profile. What is the main benefit of this approach?

medium

A. Your app gets real-time updates without delay

B. Your app must ask repeatedly for updates

C. Your app ignores updates until manually refreshed

D. Your app receives outdated information

Solution

1. Step 1: Analyze the webhook behavior

   The webhook sends a POST request immediately when the event happens, so your app gets notified right away.

2. Step 2: Understand the benefit of instant notifications

   This means your app does not need to ask repeatedly and can update its data in real time.

3. Final Answer:

   Your app gets real-time updates without delay -> Option A

4. Quick Check:

   Instant POST = real-time updates [OK]

Hint: Instant POST means real-time updates [OK]

Common Mistakes:

• Thinking app must poll for updates
• Assuming updates are delayed
• Believing webhook sends outdated info

4. You set up a webhook but your app never receives notifications. Which of these is a likely cause?

medium

A. Your app is polling the webhook URL repeatedly

B. Your app is sending POST requests to the webhook

C. Webhooks use GET requests instead of POST

D. The webhook URL is incorrect or unreachable

Solution

1. Step 1: Check webhook delivery requirements

   Webhooks send POST requests to a URL your app provides. If the URL is wrong or unreachable, notifications won't arrive.

2. Step 2: Eliminate incorrect causes

   Your app does not send POST requests to the webhook; the webhook sends them. Webhooks use POST, not GET. Polling is unrelated to webhook delivery.

3. Final Answer:

   The webhook URL is incorrect or unreachable -> Option D

4. Quick Check:

   Wrong URL = no notifications [OK]

Hint: Check webhook URL correctness first [OK]

Common Mistakes:

• Thinking app sends POST to webhook
• Confusing HTTP methods used
• Assuming polling affects webhook delivery

5. You want your app to update user data immediately when a payment is completed. Which approach best uses webhooks to achieve this?

hard

A. Send GET requests from your app to the payment server repeatedly

B. Make your app check the payment status every minute

C. Set up a webhook that sends a POST notification to your app when payment completes

D. Ignore payment updates and refresh data manually

Solution

1. Step 1: Identify the goal

   You want immediate updates when payment completes, so your app must get notified instantly.

2. Step 2: Choose the webhook approach

   Setting up a webhook that sends a POST notification on payment completion pushes updates instantly, avoiding delays and repeated checks.

3. Final Answer:

   Set up a webhook that sends a POST notification to your app when payment completes -> Option C

4. Quick Check:

   Webhook POST = instant payment update [OK]

Hint: Use webhook POST for instant payment updates [OK]

Common Mistakes:

• Relying on polling instead of webhooks
• Using GET requests incorrectly
• Ignoring real-time update needs