Pagination (from/size) in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Elasticsearch query pagination?

Given an Elasticsearch index with 10 documents numbered 1 to 10, what documents will be returned by this query?

Elasticsearch

{
  "from": 3,
  "size": 4,
  "query": {
    "match_all": {}
  }
}

A [3, 4, 5, 6]

B [4, 5, 6, 7]

C [1, 2, 3, 4]

D [7, 8, 9, 10]

💡 Hint

Remember that 'from' is zero-based and skips that many documents before returning results.

The 'from' parameter skips the first 3 documents (1, 2, 3). Then 'size' 4 returns the next 4 documents: 4, 5, 6, 7.

❓ Predict Output

intermediate

What happens if you set 'from' to 0 and 'size' to 0 in Elasticsearch?

Consider this query. What will be the result?

Elasticsearch

{
  "from": 0,
  "size": 0,
  "query": {
    "match_all": {}
  }
}

A All documents returned

B Returns one document only

C Syntax error, query fails

D No documents returned, only metadata like total hits

💡 Hint

Size 0 means no hits are returned, but metadata is still included.

Setting 'size' to 0 returns no hits but still returns metadata such as total hits count.

🔧 Debug

advanced

Why does this pagination query return an error?

This query causes an error. Identify the cause.

Elasticsearch

{
  "from": -5,
  "size": 10,
  "query": {
    "match_all": {}
  }
}

A 'from' cannot be negative, causes a validation error

B 'size' cannot be greater than 5

C Missing 'sort' field causes error

D Query syntax is invalid due to missing brackets

💡 Hint

Check the allowed range for 'from' parameter.

The 'from' parameter must be zero or positive. Negative values cause a validation error.

🧠 Conceptual

advanced

What is a limitation of using 'from' and 'size' for deep pagination in Elasticsearch?

Why is using large 'from' values with 'size' problematic in Elasticsearch?

A Performance degrades because Elasticsearch must skip many documents internally

B It causes syntax errors in the query

C It returns duplicate documents

D It limits the total number of documents returned to 1000

💡 Hint

Think about how Elasticsearch processes skipped documents.

Using large 'from' values makes Elasticsearch skip many documents internally, which slows down queries.

❓ Predict Output

expert

What is the output of this paginated query with sorting?

Given documents with field 'age' values [30, 20, 40, 10, 50], what documents are returned by this query?

Elasticsearch

{
  "from": 1,
  "size": 2,
  "sort": [{"age": "asc"}],
  "query": {
    "match_all": {}
  }
}

A [30, 40]

B [10, 20]

C [20, 30]

D [40, 50]

💡 Hint

Sort ascending by age, then skip 1 document and take 2.

Sorted ascending by age: [10, 20, 30, 40, 50]. 'from':1 skips 10, next two are 20 and 30.

Practice

1.

What does the from parameter control in an Elasticsearch query?

easy

A. The total number of results to return

B. The starting index of the search results to return

C. The sorting order of the results

D. The fields to include in the results

Solution

1. Step 1: Understand the role of from

   The from parameter sets the offset, meaning it tells Elasticsearch where to start returning results from.

2. Step 2: Differentiate from size

   The size parameter controls how many results to return, not the starting point.

3. Final Answer:

   The starting index of the search results to return -> Option B

4. Quick Check:

   from = start index [OK]

Hint: Remember: from = start index, size = count [OK]

Common Mistakes:

• Confusing from with size
• Thinking from controls sorting
• Assuming from limits total results

2.

Which of the following is the correct way to request the second page of results with 10 items per page using from and size?

{ "from": ?, "size": 10 }

easy

A. 10

B. 1

C. 11

D. 20

Solution

1. Step 1: Calculate the starting index for page 2

   Page 1 has items 0-9, so page 2 starts at index 10 (10 items per page).

2. Step 2: Set from to 10 and size to 10

   This returns items 10 to 19, which is the second page.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   Page 2 start = (2-1)*10 = 10 [OK]

Hint: from = (page_number - 1) * size [OK]

Common Mistakes:

• Using 1 instead of 10 for from
• Using 11 which skips one item
• Using 20 which is page 3 start

3.

Given this Elasticsearch query snippet, what range of results will be returned?

{ "from": 5, "size": 3 }

medium

A. Results 3 to 5

B. Results 0 to 3

C. Results 5 to 7

D. Results 6 to 8

Solution

1. Step 1: Identify the starting index

   The from value is 5, so results start from index 5.

2. Step 2: Calculate the ending index

   With size 3, results include indexes 5, 6, and 7.

3. Final Answer:

   Results 5 to 7 -> Option C

4. Quick Check:

   from=5, size=3 -> 5,6,7 [OK]

Hint: from + size - 1 = last result index [OK]

Common Mistakes:

• Assuming from is count, not start
• Off-by-one errors in range
• Mixing up start and end indexes

4.

Identify the error in this Elasticsearch pagination query:

{ "from": -5, "size": 10 }

medium

A. "from" must be zero or positive, but negative is allowed

B. "size" must be less than 10

C. No error, this query is valid

D. "from" cannot be negative

Solution

1. Step 1: Check the value of from

   The from parameter must be zero or positive; negative values are invalid.

2. Step 2: Validate size value

   The size value 10 is valid and does not cause error.

3. Final Answer:

   "from" cannot be negative -> Option D

4. Quick Check:

   Negative from is invalid [OK]

Hint: from must be ≥ 0, negative causes error [OK]

Common Mistakes:

• Allowing negative from values
• Confusing size limits
• Ignoring validation rules

5.

You want to display search results page by page with 15 results each. If the user requests page 4, what should the from and size values be to get the correct results?

hard

A. { "from": 45, "size": 15 }

B. { "from": 60, "size": 15 }

C. { "from": 30, "size": 15 }

D. { "from": 15, "size": 4 }

Solution

1. Step 1: Calculate the starting index for page 4

   Using the formula from = (page_number - 1) * size, we get (4 - 1) * 15 = 45.

2. Step 2: Set the size to 15

   Since each page shows 15 results, size remains 15.

3. Final Answer:

   { "from": 45, "size": 15 } -> Option A

4. Quick Check:

   from = 45, size = 15 for page 4 [OK]

Hint: Use from = (page-1)*size for correct pagination [OK]

Common Mistakes:

• Using from = page * size
• Swapping from and size values
• Setting size to page number