Synonyms relevance help

Elastic Stack Elasticsearch
4

Hello there,

Since you are indexing synonyms into your inverted index, brain storm and brainstorm are all different tokens after analyzer does its thing. So Elasticsearch on query time uses your analyzer to create tokens for brain, storm and brainstorm from your query and match multiple tokens with indexes 2 and 4, your index 2 has lesser words so tf/idf scores it higher between the two and index number 1 only matches brainstorm.

You can also see what your analyzer does to your input with this;

POST test_index/_analyze
{
  "analyzer": "my_search_analyzer",
  "text": "I had a storm in my brain"
}

I did some trying out so, you should change your index analyzer to my_analyzer;

PUT /test_index
{
  "settings": {
    "index": {
      "analysis": {
        "filter": {
          "my_synonyms": {
            "type": "synonym",
            "synonyms": [
              "mind, brain",
              "brainstorm,brain storm"
            ]
          }
        },
        "analyzer": {
          "my_analyzer": {
            "tokenizer": "standard",
            "filter": [
              "lowercase"
            ]
          },
          "my_search_analyzer": {
            "tokenizer": "standard",
            "filter": [
              "lowercase",
              "my_synonyms"
            ]
          }
        }
      }
    }
  },
  "mappings": {
    "properties": {
      "my_field": {
        "type": "text",
        "analyzer": "my_analyzer"
      }
    }
  }
}

Then you want to boost your exact matches, but you also want to get hits from my_search_analyzer tokens as well so i have changed your query a bit;

GET test_index/_search
{
  "query": {
    "bool": {
      "should": [
        {
          "match": {
            "my_field": {
              "query": "brainstorm",
              "analyzer": "my_search_analyzer"
            }
          }
        },
        {
          "match_phrase": {
            "my_field": {
              "query": "brainstorm"
            }
          }
        }
      ]
    }
  }
}

result:

{
  "took" : 3,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 3,
      "relation" : "eq"
    },
    "max_score" : 2.3491273,
    "hits" : [
      {
        "_index" : "test_index",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 2.3491273,
        "_source" : {
          "my_field" : "This is a brainstorm"
        }
      },
      {
        "_index" : "test_index",
        "_type" : "_doc",
        "_id" : "2",
        "_score" : 1.8185701,
        "_source" : {
          "my_field" : "A different brain storm"
        }
      },
      {
        "_index" : "test_index",
        "_type" : "_doc",
        "_id" : "4",
        "_score" : 1.4100728,
        "_source" : {
          "my_field" : "I had a storm in my brain"
        }
      }
    ]
  }
}