What is the boost factor of a should in a bool_query?

Elastic Stack Elasticsearch
1

Hi,

I'm a newbie to elasticsearch and couldn't find the answer to this in the online docs.

I have a bool_query with a must and a should. As I wanted the should part causes those results to be boosted.

However, what I can't find is what the default boost factor is when a should is matched? Is it possible to tweak this default boost factor?

Thank you

2

Welcome!

There's no "boost" factor as per say for should condition. It "just" adds the score of the should clauses to the score of the must clauses. Which effectively makes documents scoring higher.

3

thanks dadoonet.

So different types of shoulds would have different scores?

In my current tests it seems to add 1 to the score when it matches the should.

4

Could you provide a full recreation script as described in About the Elasticsearch category. It will help to better understand what you are doing. Please, try to keep the example as simple as possible.

A full reproduction script will help readers to understand, reproduce and if needed fix your problem. It will also most likely help to get a faster answer.

5

Sure dadoonet:

Index:

{
    "settings": {
        "analysis": {
            "analyzer": {
                "auto_complete_a": {
                    "tokenizer": "whitespace",
                    "filter": [
                        "lowercase",
                        "filter_a"
                    ]
                }
            },
            "filter": {
                "filter_a": {
                    "type": "edge_ngram",
                    "min_gram": 3,
                    "max_gram": 7
                }
            }
        }
    },
    "mappings": {
        "properties": {
            "name": {
                "type": "text",
                "analyzer": "auto_complete_a"
            },
            "sku": {
                "type": "text"
            }
        }
    }
}

Using this query the matching record for 111111 is scored 16.67

{
    "query": {
        "bool": {
            "must": {
                "multi_match": {
                    "query": "sony"
                }
            },
            "should": {
                "terms": {
                    "sku": ["111111", "222222"]
                }
            }
        }
    }
}

However changing the should to a filter scores it as 15.67

{
    "query": {
        "bool": {
            "must": {
                "multi_match": {
                    "query": "sony"
                }
            },
            "filter": {
                "terms": {
                    "sku": ["111111", "222222"]
                }
            }
        }
    }
}

That's why I assumed that the should would add a score of 1

6

I can't reproduce without data. Could you share a full script please?

7

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