Function score query in Elasticsearch - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a function score query in Elasticsearch?

A function score query lets you modify the score of documents returned by a query using functions like boosting, decay, or script scoring. It helps customize how results are ranked.

beginner

Name two common functions used inside a function score query.

Common functions include weight (to boost scores by a fixed number) and decay functions like gauss or exp that reduce scores based on distance from a point.

intermediate

What does the boost_mode parameter do in a function score query?

boost_mode controls how the original query score and the function score combine. Options include multiply, sum, replace, and more.

intermediate

Explain the purpose of the score_mode in a function score query.

score_mode defines how multiple functions' scores combine when more than one function applies. For example, sum adds them, multiply multiplies them, and max picks the highest.

beginner

Show a simple example of a function score query that boosts documents with a field is_featured set to true.

Example:

{
  "query": {
    "function_score": {
      "query": { "match_all": {} },
      "functions": [
        {
          "filter": { "term": { "is_featured": true } },
          "weight": 5
        }
      ],
      "boost_mode": "multiply"
    }
  }
}

What does a function score query primarily do in Elasticsearch?

A Modify the score of documents returned by a query

B Change the index mapping

C Delete documents from the index

D Create a new index

A function score query changes how documents are scored and ranked by applying functions to the original query scores.

Which parameter controls how the original score and function score combine?

A score_mode

B query_mode

C filter_mode

D boost_mode

boost_mode defines how the original query score and function score combine.

If you want to add scores from multiple functions, which score_mode should you use?

A sum

B multiply

C max

D replace

sum adds the scores from multiple functions together.

Which function would you use to boost documents with a specific field value?

A gauss

B script_score

C weight

D random_score

weight applies a fixed boost to documents matching a filter.

What is the effect of setting boost_mode to replace?

A Original score is multiplied by function score

B Function score replaces the original score

C Scores are added together

D Scores are averaged

With replace, the function score completely replaces the original query score.

Describe what a function score query is and why you might use it.

Think about how you can change the importance of search results.

Explain the difference between boost_mode and score_mode in a function score query.

One controls original vs function, the other controls multiple functions.