ElasticSearch | Randomize results with same score

Question

In ElasticSearch is it possible to randomize the order of search results with equal score without losing pagination?

I'm hosting a database with thousands of job candidates. When a company are searching for a particular skill (or a combination of skills), it's always the same order (and thus the candidates in the top of search results are having a huge advantage)

Example for a search query:

let params = {
      index: 'candidates',
      type: 'candidate',
      explain: true,
      size: size,
      from: from,
      body: {
        _source: {
          includes: ['firstName', 'middleName', 'lastName']
        },
        query: {
          bool: {
            must: [/* Left out */],
            should: [/* Left out */],
          }
        }
      }
    };

You could use rescoring to randomize top-K results.

Polynomial Proton
– Polynomial Proton

2020-02-22 18:39:15 +00:00
Commented Feb 22, 2020 at 18:39 — Polynomial Proton
– Polynomial Proton, Commented Feb 22, 2020 at 18:39

Mitar · Accepted Answer · 2022-10-04 20:45:36Z

1

Henry's answer is good, but I think it is easier to do:

        function_score: {
          query: {
            ...
          },
          random_score: {
            seed: 12345678910,
            field: '_seq_no',
            weight: 0.0001
          },
          boost_mode: 'sum'

So there is no need to boost the original score, just weight the random score down so that it contributes little (but still enough to break ties).

I do dislike such approach to break ties though, because even if you are contributing just a little to the score, you could still change order of results between results which do not have the same score, but have the score very close. This is why I opened this feature request.

answered Oct 4, 2022 at 20:45

Mitar

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Comments

Henry · Accepted Answer · 2021-01-13 16:04:09Z

You could use a function_score query, wrap your bool query in it and add a random_score function. Next step is to find the good weighting that match your needs using "boost" and "boost_mode" or "weight"...

Note that if you use filters the output score will be 0 so you will need to change the "boost_mode" from "multiply" to "replace", "sum" or something else...

Finally, don't forget to add a seed (and field as of ES 7.0) to the random_score to keep a near-consistent pagination

From your example I would suggest something like :

let params = {
      ...
      body: {
        ...
        function_score: {
          query: {
            bool: {
              must: [/* Left out */],
              should: [/* Left out */],
              boost: 100
            }
          },
          random_score: {
            seed: 12345678910,
            field: '_seq_no'
          },
          boost_mode: 'sum'
        }
      }
    };

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