Dis max query in Elasticsearch - Step-by-Step Execution

Concept Flow - Dis max query

Start Dis Max Query

↓

Evaluate Each Query

↓

Calculate Scores

↓

Select Max Score

↓

Add Tie Breaker Score

↓

Return Final Score

Dis max query runs multiple queries, picks the highest score, adds a tie breaker, and returns the final score.

Execution Sample

Elasticsearch

{
  "dis_max": {
    "queries": [
      { "match": { "title": "apple" } },
      { "match": { "description": "apple" } }
    ],
    "tie_breaker": 0.3
  }
}

This query searches 'apple' in title and description fields, picks the best score, and adds 30% of other scores.

Execution Table

Step	Query Evaluated	Score	Max Score So Far	Tie Breaker Contribution	Final Score
1	match title: apple	2.0	2.0	0	2.0
2	match description: apple	1.5	2.0	0.45	2.45
3	End	-	2.0	0.45	2.45

💡 All queries evaluated; max score 2.0 plus tie breaker 0.45 gives final score 2.45

Variable Tracker

Variable	Start	After Query 1	After Query 2	Final
max_score	0	2.0	2.0	2.0
tie_breaker_sum	0	0	1.5	1.5
final_score	0	2.0	2.45	2.45

Key Moments - 2 Insights

Why does the final score include a tie breaker value?

The tie breaker adds a fraction of the other query scores to the max score, as shown in step 2 of the execution_table, to improve relevance when multiple queries match.

What if one query score is much higher than others?

The max score dominates the final score, but the tie breaker still adds a small part of other scores, ensuring they influence ranking slightly (see variable_tracker final values).

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what is the tie breaker contribution?

A 0

B 0.45

C 1.5

D 2.0

💡 Hint

Check the 'Tie Breaker Contribution' column at step 2 in the execution_table.

At which step does the max score get set to 2.0?

A Step 1

B Step 2

C Step 3

D Start

💡 Hint

Look at the 'Max Score So Far' column in the execution_table.

If tie_breaker was 0, what would the final score be after step 2?

A 1.5

B 2.45

C 2.0

D 0

💡 Hint

Refer to how tie breaker adds to final score in the execution_table and variable_tracker.

Concept Snapshot

Dis max query runs multiple queries,
picks the highest score,
adds tie_breaker * sum of other scores,
and returns the combined final score.
Use tie_breaker to balance relevance from multiple fields.

Full Transcript

The Dis max query in Elasticsearch evaluates multiple queries and picks the highest score among them. It then adds a tie breaker value, which is a fraction of the other query scores, to the max score. This helps improve relevance when multiple queries match. In the example, two queries search for 'apple' in title and description fields. The first query scores 2.0, the second 1.5. The max score is 2.0. The tie breaker is 0.3, so 0.3 times 1.5 equals 0.45. Adding this to 2.0 gives a final score of 2.45. Variables like max_score, tie_breaker_sum, and final_score update step by step. This process ensures the best matching query dominates but others still influence the result slightly.

Practice

1. What is the main purpose of the dis_max query in Elasticsearch?

easy

A. To select the highest score from multiple queries to find the best match

B. To combine all scores from multiple queries by summing them

C. To filter documents based on a single exact match

D. To sort documents alphabetically by a field

Solution

1. Step 1: Understand the dis_max query behavior

   The dis_max query evaluates multiple queries and picks the highest score among them for each document.

2. Step 2: Compare with other scoring methods

   Unlike sum or filter queries, dis_max focuses on the best single match score, not combined or filtered results.

3. Final Answer:

   To select the highest score from multiple queries to find the best match -> Option A

4. Quick Check:

   dis_max picks highest score = A [OK]

Hint: Remember: dis_max picks the best single score, not sums [OK]

Common Mistakes:

• Thinking dis_max sums scores from all queries
• Confusing dis_max with filter queries
• Assuming dis_max sorts documents alphabetically

2. Which of the following is the correct syntax to use a dis_max query with two match queries in Elasticsearch?

easy

A. {\"dis_max\": {\"queries\": {\"match\": {\"field1\": \"value1\"}, \"match\": {\"field2\": \"value2\"}}}}

B. {\"dis_max\": [{\"match\": {\"field1\": \"value1\"}}, {\"match\": {\"field2\": \"value2\"}}]}

C. {\"dis_max\": {\"queries\": [{\"match\": {\"field1\": \"value1\"}}, {\"match\": {\"field2\": \"value2\"}}]}}

D. {\"dis_max\": {\"query\": [{\"match\": {\"field1\": \"value1\"}}, {\"match\": {\"field2\": \"value2\"}}]}}

Solution

1. Step 1: Check the dis_max query structure

   The dis_max query requires a queries array containing individual query objects.

2. Step 2: Validate the JSON syntax

   {\"dis_max\": {\"queries\": [{\"match\": {\"field1\": \"value1\"}}, {\"match\": {\"field2\": \"value2\"}}]}} correctly uses queries as an array with two match queries inside separate objects.

3. Final Answer:

   {"dis_max": {"queries": [{"match": {"field1": "value1"}}, {"match": {"field2": "value2"}}]}} -> Option C

4. Quick Check:

   dis_max uses queries array = D [OK]

Hint: dis_max needs a 'queries' array, not 'query' or object [OK]

Common Mistakes:

• Using 'query' instead of 'queries' key
• Passing queries as an object instead of an array
• Omitting the array brackets around queries

3. Given this Elasticsearch query snippet using dis_max with tie_breaker set to 0.3:

{
  "dis_max": {
    "queries": [
      { "match": { "title": "apple" } },
      { "match": { "description": "apple" } }
    ],
    "tie_breaker": 0.3
  }
}

What effect does the tie_breaker parameter have on the scoring?

medium

A. It adds 30% of the scores from non-highest matching queries to the final score

B. It multiplies the highest score by 0.3

C. It ignores all but the highest scoring query

D. It subtracts 0.3 from the highest score

Solution

1. Step 1: Understand tie_breaker in dis_max

   The tie_breaker adds a fraction of the scores from other matching queries to the highest score.

2. Step 2: Apply the 0.3 value meaning

   With tie_breaker 0.3, 30% of the other query scores are added to the highest score, boosting documents matching multiple queries.

3. Final Answer:

   It adds 30% of the scores from non-highest matching queries to the final score -> Option A

4. Quick Check:

   tie_breaker 0.3 adds 30% other scores = C [OK]

Hint: tie_breaker adds fraction of other scores to highest score [OK]

Common Mistakes:

• Thinking tie_breaker multiplies highest score directly
• Assuming tie_breaker ignores other queries
• Believing tie_breaker subtracts from scores

4. You wrote this dis_max query but it returns an error:

{
  "dis_max": {
    "queries": {
      { "match": { "field1": "value1" } },
      { "match": { "field2": "value2" } }
    }
  }
}

What is the error and how to fix it?

medium

A. The dis_max query requires a boost parameter

B. The queries value should be an array, not an object; replace curly braces with square brackets

C. The match queries must be inside a 'query' key, not 'queries'

D. The field names must be strings without quotes

Solution

1. Step 1: Identify the queries structure error

   The queries key must hold an array of query objects, but curly braces {} were used, making it an object.

2. Step 2: Correct the syntax

   Replace the curly braces around the queries with square brackets [] to form a valid array.

3. Final Answer:

   The queries value should be an array, not an object; replace curly braces with square brackets -> Option B

4. Quick Check:

   queries must be array [] not object {} = A [OK]

Hint: Use [] for queries array, not {} [OK]

Common Mistakes:

• Using curly braces instead of square brackets for queries
• Adding unnecessary boost parameter causing errors
• Removing quotes from field names

5. You want to boost the importance of a dis_max query compared to other queries in your Elasticsearch search. Which is the correct way to apply a boost to the entire dis_max query?

hard

A. { "dis_max": { "boost": 2.0, "tie_breaker": 0.5 } }

B. { "dis_max": { "queries": [...], "boost": "high" } }

C. { "dis_max": { "queries": [...], "tie_breaker": 2.0 } }

D. { "dis_max": { "queries": [...], "boost": 2.0 } }

Solution

1. Step 1: Understand boost usage in dis_max

   The boost parameter is applied at the dis_max query level to increase its overall importance.

2. Step 2: Validate correct boost syntax

   Boost must be a numeric value; { "dis_max": { "queries": [...], "boost": 2.0 } } correctly places boost: 2.0 inside dis_max alongside queries.

3. Final Answer:

   { "dis_max": { "queries": [...], "boost": 2.0 } } -> Option D

4. Quick Check:

   Boost is numeric and inside dis_max = B [OK]

Hint: Put numeric boost inside dis_max alongside queries [OK]

Common Mistakes:

• Using non-numeric boost values like strings
• Placing boost outside dis_max query
• Confusing tie_breaker with boost