Elasticsearch Elasticsearch Sort by Boolean: Advanced Techniques and Best Practices

By Opster Team

Updated: Jun 19, 2023

| 2 min read

Introduction

Sorting documents in Elasticsearch based on boolean fields can be a common requirement in various use cases. In this article, we will discuss advanced techniques and best practices for sorting documents by boolean fields in Elasticsearch.

1. Sorting by boolean fields using script-based sorting

Elasticsearch allows you to use script-based sorting to sort documents based on custom logic. You can use this feature to sort documents by boolean fields. Here’s an example of how to sort documents by a boolean field called “is_featured”:

GET /_search
{
  "query": {
    "match_all": {}
  },
  "sort": [
    {
      "_script": {
        "type": "number",
        "script": {
          "source": "doc['is_featured'].value ? 1 : 0",
          "lang": "painless"
        },
        "order": "desc"
      }
    }
  ]
}

In this example, we use a Painless script to assign a value of 1 to documents with “is_featured” set to true and a value of 0 to documents with “is_featured” set to false. The documents are then sorted in descending order based on these values.

2. Using a boolean field as a tiebreaker in sorting

In some cases, you may want to sort documents based on multiple fields, with the boolean field acting as a tiebreaker. For example, you might want to sort documents by a numeric field called “score” and use the “is_featured” boolean field as a tiebreaker. Here’s how you can achieve this:

GET /_search
{
  "query": {
    "match_all": {}
  },
  "sort": [
    {
      "score": {
        "order": "desc"
      }
    },
    {
      "_script": {
        "type": "number",
        "script": {
          "source": "doc['is_featured'].value ? 1 : 0",
          "lang": "painless"
        },
        "order": "desc"
      }
    }
  ]
}

In this example, documents are first sorted by the “score” field in descending order. If two documents have the same score, the “is_featured” boolean field is used as a tiebreaker, with documents having “is_featured” set to true appearing before those with “is_featured” set to false.

3. Optimizing performance when sorting by boolean fields

Sorting by boolean fields using script-based sorting can have an impact on performance, especially when dealing with large datasets. To optimize performance, consider the following best practices:

• Use doc values: Doc values are an on-disk data structure that allows Elasticsearch to access field values directly from disk during sorting, rather than loading them into memory. Make sure that the boolean field you’re sorting by has doc values enabled. By default, doc values are enabled for all fields except for analyzed text fields.

• Cache scripts: Elasticsearch can cache compiled scripts to improve performance. To enable caching for a script, add the “params” object to the script definition and use parameters instead of hardcoding values in the script. For example:

  "script": {
    "source": "doc[params.field].value ? 1 : 0",
    "lang": "painless",
    "params": {
      "field": "is_featured"
    }
  }

• Use filters instead of sorting: If you only need to retrieve documents with a specific boolean value, consider using a filter query instead of sorting. Filtering is generally faster than sorting, as it doesn’t require scoring or sorting all documents in the index.

Conclusion 

In conclusion, sorting documents in Elasticsearch by boolean fields can be achieved using script-based sorting and can be optimized by following best practices. By understanding these techniques, you can effectively sort documents based on boolean fields and improve the performance of your Elasticsearch queries.