Question

In ElasticSearch, I’ve created two documents with one field, “CategoryMajor”

In doc1, I set CategoryMajor to “Restaurants”

In doc2, I set CategoryMajor to “Restaurants Restaurants Restaurants Restaurants Restaurants”

If I perform a search for CategoryMajor:Restaurants, doc1 shows up as MORE RELEVANT than doc2. Which is not typical Lucene behavior, which gives more relevance the more times a term shows up. doc2 should be MORE RELEVANT than doc1.

How in do I fix this?

Answer 1

You can add &explain=true to your GET query to see that score of doc2 is lowered by “fieldNorm” factor. This is caused by default lucene similarity calculation formula, which lowers score for longer documents. Please read this document about default lucene similarity formula:

http://lucene.apache.org/core/3_6_0/api/all/org/apache/lucene/search/Similarity.html

To disable this behaviour add “omit_norms=true” for CategoryMajor field to your index mapping by sending PUT request to:

http://localhost:9200/index/type/_mapping

with request body:

{
    "type": {
         properties": {
            "CategoryMajor": {
                "type": "string",
                "omit_norms": "true"
           }
        }
    }
}

I’m not certain, but it may be necessary to delete your index, create it again, put above mapping and then reindex your documents. Reindexing after changing mapping is necessary for sure :).