Offset-based pagination in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this offset-based pagination calculation?

Given a REST API that uses offset-based pagination, the client requests page 3 with a page size of 10. What is the offset value sent to the server?

Rest API

page = 3
page_size = 10
offset = (page - 1) * page_size
print(offset)

A 20

B 30

C 3

D 10

💡 Hint

Offset is how many items to skip before starting to collect the page.

Offset is calculated as (page - 1) * page_size. For page 3 and page size 10, offset = (3 - 1) * 10 = 20.

🧠 Conceptual

intermediate

Which statement best describes offset-based pagination?

Choose the statement that correctly describes offset-based pagination in REST APIs.

A It only works with APIs that return data sorted by timestamp.

B It uses a page number and page size to calculate how many items to skip before fetching data.

C It fetches all data at once and then slices it on the client side.

D It uses a cursor to mark the last item fetched and fetches the next set after it.

💡 Hint

Think about how offset is calculated using page number and size.

Offset-based pagination calculates the number of items to skip using page number and page size, then fetches the next set of items.

🔧 Debug

advanced

Why does this offset-based pagination code return an empty list on page 1?

Look at the code below. It is supposed to return the first page of results but returns an empty list. What is the cause?

Rest API

def get_page(data, page, page_size):
    offset = page * page_size
    return data[offset:offset + page_size]

items = list(range(5))
print(get_page(items, 1, 10))

A The slice syntax is incorrect; it should be data[offset:page_size].

B The data list is empty, so it always returns an empty list.

C The offset calculation should subtract 1 from page before multiplying by page_size.

D The page_size should be added to offset twice.

💡 Hint

Remember that page 1 means no items skipped.

Offset should be (page - 1) * page_size. The current code skips the first page entirely by starting at offset = page * page_size.

📝 Syntax

advanced

Which option correctly implements offset-based pagination in Python?

Choose the code snippet that correctly calculates offset and slices the data list for pagination.

Rest API

data = list(range(100))
page = 4
page_size = 15

A

offset = (page - 1) * page_size
page_data = data[offset:offset + page_size]

B

offset = page * page_size
page_data = data[offset:offset + page_size]

C

offset = (page + 1) * page_size
page_data = data[offset:offset + page_size]

D

offset = page_size - page
page_data = data[offset:offset + page_size]

💡 Hint

Offset must skip items from previous pages.

Offset is (page - 1) * page_size to skip items from earlier pages. Then slice from offset to offset + page_size.

🚀 Application

expert

How many items will be returned by this offset-based pagination request?

Assume a dataset of 95 items. A client requests page 10 with a page size of 10 using offset-based pagination. How many items will the server return?

A 0

B 10

C 15

D 5

💡 Hint

Calculate offset and see how many items remain after skipping.

Offset = (10 - 1) * 10 = 90. There are 95 items total, so 95 - 90 = 5 items remain to return.

Practice

1. What does offset represent in offset-based pagination?

easy

A. The maximum number of pages available

B. The total number of items to return in the response

C. The current page number being requested

D. The number of items to skip before starting to collect results

Solution

1. Step 1: Understand the role of offset

   Offset tells the system how many items to skip before starting to return data.

2. Step 2: Differentiate offset from limit and page

   Limit controls how many items to return; page number is a different pagination method.

3. Final Answer:

   The number of items to skip before starting to collect results -> Option D

4. Quick Check:

   Offset = items skipped before results [OK]

Hint: Offset means how many items to skip before fetching [OK]

Common Mistakes:

• Confusing offset with limit
• Thinking offset is the page number
• Assuming offset is total items count

2. Which of the following is the correct way to request the second page of results with 10 items per page using offset-based pagination?

easy

A. GET /items?start=10&count=10

B. GET /items?offset=10&limit=10

C. GET /items?page=2&limit=10

D. GET /items?offset=2&limit=10

Solution

1. Step 1: Calculate offset for page 2 with 10 items per page

   Offset = (page number - 1) * limit = (2 - 1) * 10 = 10.

2. Step 2: Identify correct query parameters

   Offset and limit are standard; page parameter is not used in offset-based pagination.

3. Final Answer:

   GET /items?offset=10&limit=10 -> Option B

4. Quick Check:

   Offset = 10 for page 2 with 10 items [OK]

Hint: Offset = (page - 1) x limit for correct pagination [OK]

Common Mistakes:

• Using page instead of offset
• Setting offset to page number directly
• Using non-standard parameter names

3. Given the API call GET /products?offset=5&limit=3 and the product list ["A", "B", "C", "D", "E", "F", "G", "H"], what will be the returned products?

medium

A. ["D", "E", "F"]

B. ["E", "F", "G"]

C. ["F", "G", "H"]

D. ["G", "H"]

Solution

1. Step 1: Identify starting index using offset

   Offset 5 means skip first 5 items: A(0), B(1), C(2), D(3), E(4) skipped; start at index 5.

2. Step 2: Select limit number of items from offset

   Limit is 3, so select items at indices 5, 6, 7: F, G, H.

3. Final Answer:

   ["F", "G", "H"] -> Option C

4. Quick Check:

   Offset 5 + limit 3 = F, G, H [OK]

Hint: Start at offset index, take limit items [OK]

Common Mistakes:

• Starting at offset - 1 index
• Including offset item in skipped items
• Returning fewer or more items than limit

4. You have this API call: GET /users?offset=20&limit=10. The API returns an empty list even though there are 25 users total. What is the likely problem?

medium

A. Offset is too large, skipping all remaining users

B. Limit is too small to return any users

C. Offset and limit parameters are swapped

D. API does not support offset-based pagination

Solution

1. Step 1: Calculate remaining items after offset

   Offset 20 skips first 20 users; only 5 users remain (25 - 20 = 5).

2. Step 2: Understand why empty list is returned

   API returns empty list likely because it expects at least 10 items (limit), but only 5 remain; some APIs may return empty if offset exceeds total count.

3. Final Answer:

   Offset is too large, skipping all remaining users -> Option A

4. Quick Check:

   Offset > total users - limit causes empty results [OK]

Hint: Check if offset skips beyond total items [OK]

Common Mistakes:

• Assuming limit controls start position
• Swapping offset and limit values
• Ignoring total item count in pagination

5. You want to implement offset-based pagination for a large dataset but want to avoid performance issues with very large offsets. Which approach is best to improve performance?

hard

A. Use keyset pagination by filtering with a unique indexed column instead of offset

B. Increase the limit value to reduce the number of pages

C. Cache all pages in memory to avoid database queries

D. Use offset with very large values and rely on database optimization

Solution

1. Step 1: Understand offset performance issues

   Large offsets cause the database to scan many rows before returning results, slowing queries.

2. Step 2: Identify better pagination method

   Keyset pagination uses a unique indexed column (like ID) to fetch next pages efficiently without scanning skipped rows.

3. Step 3: Evaluate other options

   Increasing limit or caching is not scalable; relying on database optimization alone is insufficient.

4. Final Answer:

   Use keyset pagination by filtering with a unique indexed column instead of offset -> Option A

5. Quick Check:

   Keyset pagination avoids large offset performance issues [OK]

Hint: Use keyset pagination to avoid slow large offsets [OK]

Common Mistakes:

• Relying on large offset values for deep pages
• Increasing limit without considering user experience
• Assuming caching solves pagination performance