Hi,
I was trying to understand scores for the following multi_match query using explain: true:
GET /myindex/_search
{
"size": 5,
"explain": true,
"_source": false,
"query": {
"bool": {
"minimum_should_match": 1,
"should": [
{
"multi_match": {
"query": "hand sanitizer",
"type": "most_fields",
"operator": "and",
"fields": [
"name",
"search_terms",
]
}
}
]
}
}
}
I get the following result with some keys omitted for clarity
{
"_shards": {
"total": 1,
"successful": 1,
"skipped": 0,
"failed": 0
},
"hits": {
"total": 12,
"max_score": 21.46976,
"hits": [
{
"_shard": "[myindex][0]",
"_node": "p1a37bfBRC6CIhegIYWJkA",
"_index": "myindex",
"_type": "doc",
"_id": "1168",
"_score": 21.46976,
"_explanation": {
"value": 21.46976,
"description": "sum of:",
"details": [
{
"value": 21.46976,
"description": "sum of:",
"details": [
{
"value": 9.661456,
"description": "sum of:",
"details": [
{
"value": 3.725314,
"description": "weight(name:hand in 5739) [PerFieldSimilarity], result of:",
"details": [
{
"value": 3.725314,
"description": "score(doc=5739,freq=1.0 = termFreq=1.0\n), product of:",
"details": [
{
"value": 3.1846268,
"description": "idf, computed as log(1 + (docCount - docFreq + 0.5) / (docFreq + 0.5)) from:",
"details": [
{
"value": 69,
"description": "docFreq",
"details": []
},
{
"value": 1678,
"description": "docCount",
"details": []
}
]
},
{
"value": 1.1697804,
"description": "tfNorm, computed as (freq * (k1 + 1)) / (freq + k1 * (1 - b + b * fieldLength / avgFieldLength)) from:",
"details": [
{
"value": 1,
"description": "termFreq=1.0",
"details": []
},
{
"value": 1.2,
"description": "parameter k1",
"details": []
},
{
"value": 0.75,
"description": "parameter b",
"details": []
},
{
"value": 48.045887,
"description": "avgFieldLength",
"details": []
},
{
"value": 31,
"description": "fieldLength",
"details": []
}
]
}
]
}
]
},
{
"value": 5.936142,
"description": "weight(name:sanitizer in 5739) [PerFieldSimilarity], result of:",
"details": [
{
"value": 5.936142,
"description": "score(doc=5739,freq=1.0 = termFreq=1.0\n), product of:",
"details": [ "omitted for char count" ]
}
]
}
]
},
{
"value": 11.808305,
"description": "sum of:",
"details": [
{
"value": 5.508706,
"description": "weight(search_terms:hand in 5739) [PerFieldSimilarity], result of:",
"details": [
{
"value": 5.508706,
"description": "score(doc=5739,freq=6.0 = termFreq=6.0\n), product of:",
"details": [ "omitted for char count" ]
}
]
},
{
"value": 6.2995987,
"description": "weight(search_terms:sanitizer in 5739) [PerFieldSimilarity], result of:",
"details": [
{
"value": 6.2995987,
"description": "score(doc=5739,freq=2.0 = termFreq=2.0\n), product of:",
"details": [ "omitted for char count" ]
}
]
}
]
}
]
},
{
"value": 0,
"description": "match on required clause, product of:",
"details": [
{
"value": 0,
"description": "# clause",
"details": []
},
{
"value": 1,
"description": "DocValuesFieldExistsQuery [field=_primary_term]",
"details": []
}
]
}
]
}
}
]
}
}
It appears to only be summing the scores for the matches in each field, not summing them and dividing by the number of match clauses as documented. Is this expected?
I found a similar forum topic with no response.
Additionally, if anyone can explain the match on required clause, product of: part, I would appreciate that too 
I'm using docker image elasticsearch:6.6.0.