In [prioritising-clauses] we explained how you could use the boost parameter at search time to give one query clause more importance than another. For instance:

1. The title query clause is twice as important as the content query clause, because it has been boosted by a factor of 2.

2. A query clause without a boost value has a neutral boost of 1.

Query-time boosting is the main tool that you can use to tune relevance. Any type of query accepts a boost parameter. Setting a boost of 2 doesn’t simply double the final _score — the actual boost value that is applied goes through normalization and some internal optimization. However, it does imply that a clause with a boost of 2 is twice as important as a clause with a boost of 1.

Practically, there is no simple formula for deciding on the correct'' boost value for a particular query clause. It’s a matter of try-it-and-see. Remember that boost is just one of the factors involved in the relevance score — it has to compete with the other factors. For instance in the above example, the title field will probably already have a natural'' boost over the content field thanks to the field length norm — titles are usually shorter than the related content — so don’t blindly boost fields just because you think they should be boosted. Apply a boost and check the results. Change the boost and check again.

Boosting an index

GET /docs_2014_*/_search (1)
{
  "indices_boost": { (2)
    "docs_2014_10": 3,
    "docs_2014_09": 2
  },
  "query": {
    "match": {
      "text": "quick brown fox"
    }
  }
}

t.getBoost()