Using the function score query

This kind of query is one of the most powerful queries that are available. This is because it allows extensive customization of a scoring algorithm. The function_score query allows us to define a function that controls the score of the documents that are returned by a query.

Generally, these functions are CPU-intensive, and executing them on a large dataset (for instance, millions of records) requires a lot of memory and time, but computing them on a small subset can significantly improve the search quality.

The common scenarios used for this query are listed as follows:

• Creating a custom score function (for example, with the decay function)
• Creating a custom boost factor, for example, based on another field (that is, boosting a document by distance from a point)
• Creating a custom filter score function, for example, based on scripting Elasticsearch capabilities
• Ordering the documents randomly

Getting ready

You will...