ElasticSearch inconsistent relevance - elasticsearch

Question

I'm using elasticsearch to do search for movies by the actors that played in them. When I search for e.g. "leonardo dicaprio" there are 10 or so movies that I get back but they all have a different score. Since they all have the same actor I would expect them to have the same score. Is anyone able to shed some light on why this is happening and hopefully how to stop it?
Elasticsearch version 1.7.2
Mapping:
{
"programs": {
"mappings": {
"program_doc_type": {
"properties": {
"cast": {
"type": "string",
"analyzer": "keyword_analyzer",
"fields": {
"name": {
"type": "string",
"analyzer": "name_analyzer"
}
}
},
"django_id": {
"type": "integer"
},
"has_poster": {
"type": "boolean"
},
"imdb_id": {
"type": "string",
"index": "not_analyzed"
},
"kind": {
"type": "string",
"index": "not_analyzed"
},
"record_url_count": {
"type": "integer"
},
"release_date": {
"type": "date",
"format": "dateOptionalTime"
},
"release_year": {
"type": "integer"
},
"title": {
"type": "string",
"analyzer": "pattern"
},
"tms_id": {
"type": "string",
"index": "not_analyzed"
}
}
}
}
}
}
Analyzers:
"analysis": {
"analyzer": {
"keyword_analyzer": {
"type": "custom",
"filter": [
"lowercase"
],
"tokenizer": "keyword"
},
"name_analyzer": {
"type": "custom",
"filter": [
"lowercase"
],
"tokenizer": "whitespace"
}
}
}
Query:
{
"query": {
"match": {"cast.name": "leonardo dicaprio"}
}
}
First Page Result:
{
"took": 12,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 62,
"max_score": 12.046804,
"hits": [
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "1077511",
"_score": 12.046804,
"_source": {
"imdb_id": "tt4007278",
"tms_id": "",
"record_url_count": 0,
"release_date": "2014-08-20",
"title": "Carbon",
"has_poster": false,
"release_year": 2014,
"django_id": 1077511,
"kind": "movie",
"cast": [
"Leonardo DiCaprio"
]
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "812919",
"_score": 11.906615,
"_source": {
"imdb_id": "tt2076929",
"tms_id": "",
"record_url_count": 0,
"title": "Satori",
"has_poster": false,
"release_year": 2014,
"django_id": 812919,
"kind": "N/A",
"cast": [
"Leonardo DiCaprio"
]
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "376792",
"_score": 11.886408,
"_source": {
"imdb_id": "tt0402538",
"tms_id": "",
"record_url_count": 0,
"title": "Titanic: The Premiere",
"has_poster": true,
"release_year": 2000,
"django_id": 376792,
"kind": "movie",
"cast": [
"Leonardo DiCaprio"
]
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "306106",
"_score": 11.69776,
"_source": {
"imdb_id": "tt0325727",
"tms_id": "",
"record_url_count": 0,
"release_date": "1998-08-16",
"title": "Leo Mania",
"has_poster": true,
"release_year": 1998,
"django_id": 306106,
"kind": "movie",
"cast": [
"Leonardo DiCaprio"
]
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "269743",
"_score": 9.637444,
"_source": {
"imdb_id": "tt0286234",
"tms_id": "",
"record_url_count": 0,
"title": "Total Eclipse",
"has_poster": false,
"release_year": 1995,
"django_id": 269743,
"kind": "movie",
"cast": [
"Leonardo DiCaprio",
"Agnieszka Holland"
]
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "840945",
"_score": 9.358208,
"_source": {
"imdb_id": "tt2195237",
"tms_id": "",
"record_url_count": 0,
"release_date": "2004-12-01",
"title": "MovieReal: The Aviator",
"has_poster": false,
"release_year": 2004,
"django_id": 840945,
"kind": "series",
"cast": [
"Leonardo DiCaprio",
"Martin Scorsese"
]
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "382168",
"_score": 9.358208,
"_source": {
"imdb_id": "tt0408269",
"tms_id": "",
"record_url_count": 0,
"release_date": "1998-09-29",
"title": "To Leo with Love",
"has_poster": true,
"release_year": 1998,
"django_id": 382168,
"kind": "movie",
"cast": [
"Jo Wyatt",
"Leonardo DiCaprio"
]
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "846212",
"_score": 7.2280827,
"_source": {
"imdb_id": "tt2218442",
"tms_id": "",
"record_url_count": 0,
"title": "Legacy of Secrecy",
"has_poster": false,
"release_year": 1947,
"django_id": 846212,
"kind": "N/A",
"cast": [
"Leonardo DiCaprio",
"Robert De Niro",
"D'Anthony Palms"
]
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "595027",
"_score": 7.1439695,
"_source": {
"imdb_id": "tt1294988",
"tms_id": "",
"record_url_count": 0,
"release_date": "2006-09-27",
"title": "Emporio Armani 'Red' One Night Only",
"has_poster": false,
"release_year": 2006,
"django_id": 595027,
"kind": "movie",
"cast": [
"Kim Cattrall",
"Leonardo DiCaprio",
"Beyoncé Knowles"
]
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "752646",
"_score": 7.1439695,
"_source": {
"imdb_id": "tt1826731",
"tms_id": "",
"record_url_count": 0,
"release_date": "2009-06-02",
"title": "Lives of Quiet Desperation: The Making of Revolutionary Road",
"has_poster": false,
"release_year": 2009,
"django_id": 752646,
"kind": "movie",
"cast": [
"Kathy Bates",
"Leonardo DiCaprio",
"Kate Winslet"
]
}
}
]
}
}
UPDATE:
I disabled field length norm and that seems to have improved it a lot but they still aren't all the same. I'm still confused. According to what i've read there are three ways to determine relevancy:
Term frequency
Inverse document frequency
Field length norm (disabled)
Since each program only has Leonardo Dicaprio one time it seems to me that they should have identical scores but they don't. Maybe i'm misunderstanding. Here are the updated settings after disabling field length norm:
Mapping:
{
"programs": {
"mappings": {
"program_doc_type": {
"properties": {
"cast": {
"type": "string",
"norms": {
"enabled": false
},
"analyzer": "keyword_analyzer",
"fields": {
"name": {
"type": "string",
"norms": {
"enabled": false
},
"analyzer": "name_analyzer"
}
}
},
"django_id": {
"type": "integer"
},
"has_poster": {
"type": "boolean"
},
"imdb_id": {
"type": "string",
"index": "not_analyzed"
},
"kind": {
"type": "string",
"index": "not_analyzed"
},
"record_url_count": {
"type": "integer"
},
"release_date": {
"type": "date",
"format": "dateOptionalTime"
},
"release_year": {
"type": "integer"
},
"title": {
"type": "string",
"analyzer": "pattern"
},
"tms_id": {
"type": "string",
"index": "not_analyzed"
}
}
}
}
}
}
First Page Result:
{
"took": 20,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 836,
"max_score": 13.778852,
"hits": [
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "421026",
"_score": 13.778852,
"_source": {
"tms_id": "",
"django_id": 421026,
"imdb_id": "tt0449557",
"has_poster": false,
"release_date": "2005-05-24",
"kind": "movie",
"cast": [
"Leonardo DiCaprio",
"Jeffrey M. Schwartz",
"Donald L. Barlett",
"James B. Steele"
],
"release_year": 2005,
"record_url_count": 0,
"title": "The Affliction of Howard Hughes: Obsessive-Compulsive Disorder"
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "555015",
"_score": 13.778852,
"_source": {
"tms_id": "MV002510340000",
"django_id": 555015,
"imdb_id": "tt1130884",
"has_poster": true,
"release_date": "2010-02-19",
"kind": "movie",
"cast": [
"Leonardo DiCaprio",
"Mark Ruffalo",
"Ben Kingsley",
"Max von Sydow"
],
"release_year": 2010,
"record_url_count": 2,
"title": "Shutter Island"
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "104669",
"_score": 13.778852,
"_source": {
"tms_id": "",
"django_id": 104669,
"imdb_id": "tt0108330",
"has_poster": true,
"release_date": "1993-04-23",
"kind": "movie",
"cast": [
"Robert De Niro",
"Ellen Barkin",
"Leonardo DiCaprio",
"Jonah Blechman"
],
"release_year": 1993,
"record_url_count": 1,
"title": "This Boy's Life"
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "846212",
"_score": 13.778852,
"_source": {
"django_id": 846212,
"title": "Legacy of Secrecy",
"imdb_id": "tt2218442",
"has_poster": false,
"kind": "N/A",
"cast": [
"Leonardo DiCaprio",
"Robert De Niro",
"D'Anthony Palms"
],
"release_year": 1947,
"record_url_count": 0,
"tms_id": ""
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "256632",
"_score": 13.778852,
"_source": {
"django_id": 256632,
"title": "The Movie Show",
"imdb_id": "tt0271918",
"has_poster": false,
"kind": "series",
"cast": [
"Ray Brady",
"Russell Crowe",
"Larry Day",
"Leonardo DiCaprio"
],
"release_year": 1986,
"record_url_count": 0,
"tms_id": ""
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "269743",
"_score": 13.778852,
"_source": {
"django_id": 269743,
"title": "Total Eclipse",
"imdb_id": "tt0286234",
"has_poster": false,
"kind": "movie",
"cast": [
"Leonardo DiCaprio",
"Agnieszka Holland"
],
"release_year": 1995,
"record_url_count": 0,
"tms_id": ""
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "1007190",
"_score": 13.778852,
"_source": {
"tms_id": "",
"django_id": 1007190,
"imdb_id": "tt3391950",
"has_poster": false,
"release_date": "2013-12-29",
"kind": "series",
"cast": [
"Leonardo DiCaprio",
"Jonah Hill",
"Martin Scorsese",
"Terence Winter"
],
"release_year": 2013,
"record_url_count": 0,
"title": "The Hollywood Reporter in Focus"
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "1077511",
"_score": 13.778852,
"_source": {
"tms_id": "",
"django_id": 1077511,
"imdb_id": "tt4007278",
"has_poster": false,
"release_date": "2014-08-20",
"kind": "movie",
"cast": [
"Leonardo DiCaprio"
],
"release_year": 2014,
"record_url_count": 0,
"title": "Carbon"
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "302615",
"_score": 13.57246,
"_source": {
"django_id": 302615,
"title": "Directors: James Cameron",
"imdb_id": "tt0322031",
"has_poster": true,
"kind": "movie",
"cast": [
"Michael Biehn",
"James Cameron",
"Jamie Lee Curtis",
"Leonardo DiCaprio"
],
"release_year": 1997,
"record_url_count": 0,
"tms_id": ""
}
},
{
"_index": "programs",
"_type": "program_doc_type",
"_id": "509785",
"_score": 13.57246,
"_source": {
"tms_id": "",
"django_id": 509785,
"imdb_id": "tt0923573",
"has_poster": false,
"release_date": "2003-05-06",
"kind": "movie",
"cast": [
"Frank Abagnale Jr.",
"Amy Adams",
"Nathalie Baye",
"Leonardo DiCaprio"
],
"release_year": 2003,
"record_url_count": 0,
"title": "'Catch Me If You Can': The Casting of the Film"
}
}
]
}
}
The results are MUCH improved but still the last 2 have different scores than the rest of the results.

Answer 1

Elasticsearch relevancy default model is called TF/IDF. You can read more about it here.
The _score you see in your search hits is calculated by this model.
Basically, the score is a result of a calculation on three factors (more info here):
Term frequency - How often does a term appear in a specific document? TF
Inverse document frequency - How often does the term appear in all documents in the collection? IDF
Field-length norm - How long is the field?
As you can infer from the above, because each document that contains leonardo dicaprio is different in its matching terms count, length of fields and matching terms count all over the index, its relevancy score is different.
Nevertheless, you get high scores for documents that contains leonardo dicaprio than those who doesn't.
Hope it helps.