Pagination patterns in Supabase - Time & Space Complexity

Time Complexity: Pagination patterns

O(n)

Understanding Time Complexity

When fetching data in pages, the time it takes depends on how many pages and items we request.

We want to know how the number of data requests grows as we ask for more pages.

Scenario Under Consideration

Analyze the time complexity of fetching paged data using Supabase.

const pageSize = 10;
let page = 1;

const { data, error } = await supabase
  .from('items')
  .select('*')
  .range((page - 1) * pageSize, page * pageSize - 1);

// This fetches one page of items with a fixed size.

This code fetches one page of data with a fixed number of items per page.

Identify Repeating Operations

Identify the API calls, resource provisioning, data transfers that repeat.

• Primary operation: One API call to fetch a page of data.
• How many times: Once per page requested.

How Execution Grows With Input

Each page requires one API call, so more pages mean more calls.

Input Size (n pages)	Approx. API Calls/Operations
10	10 calls
100	100 calls
1000	1000 calls

Pattern observation: The number of calls grows directly with the number of pages requested.

Final Time Complexity

Time Complexity: O(n)

This means if you want to get more pages, the total work grows in a straight line with the number of pages.

Common Mistake

[X] Wrong: "Fetching more pages is just one big call, so time stays the same."

[OK] Correct: Each page requires a separate call, so more pages mean more calls and more time.

Interview Connect

Understanding how pagination scales helps you design efficient data fetching in real projects.

Self-Check

"What if we changed from page-based to cursor-based pagination? How would the time complexity change?"

Practice

1. What does the .range(from, to) method do in Supabase pagination?

easy

A. It sorts the rows between from and to indexes.

B. It limits the total number of rows returned to to.

C. It fetches rows starting from index from up to index to inclusive.

D. It skips the first from rows and returns the rest.

Solution

1. Step 1: Understand the purpose of .range(from, to)

   This method is used to select a slice of rows by index, starting at from and ending at to, inclusive.

2. Step 2: Compare options with this behavior

   Only the option stating 'It fetches rows starting from index from up to index to inclusive.' correctly describes the slicing behavior. The other options describe sorting, limiting, or skipping incorrectly.

3. Final Answer:

   It fetches rows starting from index from up to index to inclusive. -> Option C

4. Quick Check:

   .range(from, to) = fetch rows from-to inclusive [OK]

Hint: Remember range is inclusive from start to end index [OK]

Common Mistakes:

• Thinking to is exclusive
• Confusing .range with .limit
• Assuming it skips rows instead of slicing

2. Which of the following is the correct syntax to fetch page 3 with 10 items per page using Supabase's .range()?

easy

A. .range(20, 29)

B. .range(30, 39)

C. .range(21, 30)

D. .range(10, 19)

Solution

1. Step 1: Calculate start and end indexes for page 3

   Page 3 means items 21 to 30 (1-based). Since .range() uses 0-based indexes, start = (3-1)*10 = 20, end = 20 + 9 = 29.

2. Step 2: Match calculated range with options

   .range(20, 29) matches the correct 0-based slice for page 3.

3. Final Answer:

   .range(20, 29) -> Option A

4. Quick Check:

   Page 3 with 10 items = indexes 20 to 29 [OK]

Hint: Page N with size S starts at (N-1)*S [OK]

Common Mistakes:

• Using 1-based indexes directly
• Off-by-one errors in start or end
• Confusing page number with item count

3. Given this Supabase query:

const page = 2;
const pageSize = 5;
const { data } = await supabase
  .from('products')
  .select('*')
  .range((page - 1) * pageSize, page * pageSize - 1);

How many rows will data contain?

medium

A. 6

B. 10

C. 4

D. 5

Solution

1. Step 1: Calculate the range indexes

   For page 2 and pageSize 5, start = (2-1)*5 = 5, end = 2*5 - 1 = 9.

2. Step 2: Determine number of rows fetched

   Indexes 5 to 9 inclusive means 5 rows (5,6,7,8,9).

3. Final Answer:

   5 -> Option D

4. Quick Check:

   Range length = end - start + 1 = 5 [OK]

Hint: Count rows as end - start + 1 [OK]

Common Mistakes:

• Counting end index as exclusive
• Miscalculating start or end
• Assuming pageSize is ignored

4. You wrote this code to fetch page 1 with 10 items per page:

const page = 1;
const pageSize = 10;
const { data } = await supabase
  .from('orders')
  .select('*')
  .range(page * pageSize, (page + 1) * pageSize - 1);

Why does this return no rows?

medium

A. Because .range() requires the start index to be less than the end index.

B. Because the range starts at 10 instead of 0, skipping the first page.

C. Because pageSize must be 0 for the first page.

D. Because .select('*') must be called after .range().

Solution

1. Step 1: Analyze the range calculation

   For page 1 and pageSize 10, start = 1*10 = 10, end = (1+1)*10 - 1 = 19. This skips rows 0 to 9.

2. Step 2: Understand why no rows appear

   If the table has fewer than 11 rows or you want the first page, you must start at 0. Starting at 10 skips the first 10 rows.

3. Final Answer:

   Because the range starts at 10 instead of 0, skipping the first page. -> Option B

4. Quick Check:

   Page 1 start index = 0, not 10 [OK]

Hint: Page 1 starts at index 0, not page * pageSize [OK]

Common Mistakes:

• Starting range at page * pageSize instead of (page-1)*pageSize
• Misunderstanding zero-based indexing
• Incorrect order of method calls

5. You want to implement infinite scrolling with Supabase pagination. Which approach correctly fetches the next page of 15 items after receiving the first page?

hard

A. Use .range(0, 14) for first page, then .range(15, 29) for second page.

B. Use .range(1, 15) for first page, then .range(16, 30) for second page.

C. Use .range(0, 15) for first page, then .range(15, 30) for second page.

D. Use .range(0, 14) for first page, then .range(14, 29) for second page.

Solution

1. Step 1: Define correct zero-based ranges for pages

   For 15 items per page, first page is indexes 0 to 14 (15 items). Second page starts at 15 and ends at 29.

2. Step 2: Match options with correct ranges

   The option using .range(0, 14) for first page, then .range(15, 29) for second page is correct. It avoids off-by-one errors or overlaps present in the others.

3. Final Answer:

   Use .range(0, 14) for first page, then .range(15, 29) for second page. -> Option A

4. Quick Check:

   Pages must not overlap and cover all items [OK]

Hint: Next page starts at previous end + 1 [OK]

Common Mistakes:

• Overlapping ranges causing duplicate items
• Off-by-one errors in start or end indexes
• Starting second page at wrong index