Why batch operations reduce round trips in Rest API - Performance Analysis

Time Complexity: Why batch operations reduce round trips

O(n)

Understanding Time Complexity

When working with APIs, sending many requests one by one can slow things down.

We want to understand how batch operations help by reducing the number of trips between client and server.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

// Sending multiple requests one by one
for (let i = 0; i < items.length; i++) {
  await api.sendRequest(items[i]);
}

// Sending all items in one batch request
await api.sendBatchRequest(items);
    

This code shows two ways to send data: one request per item, or all items together in one batch.

Identify Repeating Operations

• Primary operation: Sending a request to the server.
• How many times: In the first case, once per item (loop runs n times). In the batch case, only once regardless of item count.

How Execution Grows With Input

As the number of items grows, the number of requests grows the same way in the first method.

Input Size (n)	Approx. Operations (Requests)
10	10 requests
100	100 requests
1000	1000 requests

Pattern observation: The number of requests grows directly with the number of items, making it slower as n grows.

Final Time Complexity

Time Complexity: O(n)

This means the time to complete grows directly with the number of items when sending requests one by one.

Common Mistake

[X] Wrong: "Sending many small requests is just as fast as one big request."

[OK] Correct: Each request has overhead like network delay, so many small requests add up and slow down the process.

Interview Connect

Understanding how batch operations reduce round trips shows you can think about efficiency beyond just code logic.

This skill helps you write faster, more scalable programs that work well in real-world networks.

Self-Check

"What if we split the items into smaller batches instead of one big batch? How would the time complexity change?"

Practice

1. Why do batch operations reduce the number of round trips in REST APIs?

easy

A. Because they send requests one by one quickly

B. Because they use a faster internet connection

C. Because they skip server authentication

D. Because they combine multiple requests into a single network call

Solution

1. Step 1: Understand what a round trip means in REST APIs

   A round trip is when your app sends a request to the server and waits for a response.

2. Step 2: Explain how batch operations affect round trips

   Batch operations group many requests into one, so only one round trip is needed instead of many.

3. Final Answer:

   Because they combine multiple requests into a single network call -> Option D

4. Quick Check:

   Batch requests reduce round trips = Because they combine multiple requests into a single network call [OK]

Hint: Batch means group requests to send once [OK]

Common Mistakes:

• Thinking batch speeds internet connection
• Believing batch skips authentication
• Assuming batch sends requests separately

2. Which of the following is the correct way to send a batch request in JSON format?

easy

A. {"requests": [{"method": "GET", "url": "/users"}]}

B. [{"method": "GET", "url": "/users"}]

C. {"request": {"method": "GET", "url": "/users"}}

D. {"methods": ["GET"], "urls": ["/users"]}

Solution

1. Step 1: Identify the standard batch request format

   Batch requests usually wrap multiple requests inside a "requests" array in a JSON object.

2. Step 2: Match the correct JSON structure

   {"requests": [{"method": "GET", "url": "/users"}]} correctly uses {"requests": [...]}, while others miss this structure or use wrong keys.

3. Final Answer:

   {"requests": [{"method": "GET", "url": "/users"}]} -> Option A

4. Quick Check:

   Batch JSON uses "requests" array = {"requests": [{"method": "GET", "url": "/users"}]} [OK]

Hint: Batch JSON wraps requests in a "requests" array [OK]

Common Mistakes:

• Using array without key "requests"
• Using singular "request" instead of plural
• Separating methods and URLs into different arrays

3. Consider this pseudo-code for sending batch requests:

batch = [
  {"method": "GET", "url": "/items/1"},
  {"method": "GET", "url": "/items/2"}
]
response = send_batch(batch)
print(len(response))

What will be the output?

medium

A. 1

B. 2

C. 0

D. Error

Solution

1. Step 1: Understand the batch request content

   The batch contains two GET requests for two different items.

2. Step 2: Analyze the response length

   Each request in the batch returns one response, so the response list length is 2.

3. Final Answer:

   2 -> Option B

4. Quick Check:

   Batch of 2 requests returns 2 responses = 2 [OK]

Hint: Batch response count matches request count [OK]

Common Mistakes:

• Assuming batch returns single combined response
• Expecting zero because of batch
• Thinking batch causes error without reason

4. You wrote this batch request code but it fails:

batch = {
  "requests": {
    "method": "GET",
    "url": "/data"
  }
}
response = send_batch(batch)

What is the main error?

medium

A. The URL should be a full URL, not a path

B. The method should be lowercase "get"

C. The "requests" key should hold a list, not a single object

D. Batch requests cannot use GET method

Solution

1. Step 1: Check the "requests" value type

   Batch requests expect "requests" to be a list of request objects, not a single object.

2. Step 2: Identify the error cause

   Using an object instead of a list causes the batch to fail because it expects multiple requests.

3. Final Answer:

   The "requests" key should hold a list, not a single object -> Option C

4. Quick Check:

   Batch "requests" must be a list = The "requests" key should hold a list, not a single object [OK]

Hint: "requests" must be a list even for one request [OK]

Common Mistakes:

• Using single object instead of list for "requests"
• Changing HTTP method case unnecessarily
• Thinking full URL is always required
• Believing GET is disallowed in batch

5. You want to update 100 user records via a REST API. Which approach best reduces round trips and improves efficiency?

hard

A. Send a single batch request containing all 100 updates

B. Send 100 separate PUT requests, one per user

C. Send one PUT request with only the first user update

D. Send 10 batch requests each with 5 updates

Solution

1. Step 1: Compare sending many requests vs batch

   Sending 100 separate requests causes 100 round trips, which is slow and inefficient.

2. Step 2: Evaluate batch request benefits

   A single batch request with all 100 updates reduces round trips to 1, saving time and network use.

3. Final Answer:

   Send a single batch request containing all 100 updates -> Option A

4. Quick Check:

   One batch request for many updates = Send a single batch request containing all 100 updates [OK]

Hint: One batch request beats many single requests [OK]

Common Mistakes:

• Sending many separate requests wastes round trips
• Sending partial updates misses data
• Splitting into many small batches adds overhead