Scoring - queryNorm differs for documents during one query

Elastic Stack Elasticsearch
1

Hi,
The ES guide states, that when computing score, "The same query
normalization factor is applied to every document" - viz
http://www.elastic.co/guide/en/elasticsearch/guide/master/practical-scoring-function.html#query-norm
But when I try this example:

curl -s -XDELETE 'localhost:9200/ttt'

curl -s -XPUT 'http://localhost:9200/ttt/tweet/1?refresh=true' -d '{
"user" : "a b"
}'
curl -s -XPUT 'http://localhost:9200/ttt/tweet/2?refresh=true' -d '{
"user" : "b c"
}'

curl -s -XGET 'localhost:9200/ttt/_search?explain=trye&format=yaml' -d '
{
"query": {
"match" : { "user" : "a b" }
}
}
'

I got this result - I highlighted the interesting parts:

took: 5
timed_out: false
_shards:
total: 5
successful: 5
failed: 0
hits:
total: 2
max_score: 0.2712221
hits:

  • _shard: 2
    _node: "_baxQafwQ0WyAAZpyIv2ow"
    _index: "ttt"
    _type: "tweet"
    _id: "1"
    _score: 0.2712221
    _source:
    user: "a b"
    _explanation:
    value: 0.27122214
    description: "sum of:"
    details:
    • value: 0.13561107
      description: "weight(user:a in 0) [PerFieldSimilarity], result of:"
      details:
      • value: 0.13561107
        description: "score(doc=0,freq=1.0), product of:"
        details:
        • value: 0.70710677
          description: "queryWeight, product of:"
          details:
          • value: 0.30685282
            description: "idf(docFreq=1, maxDocs=1)"
          • value: 2.3043842
            description: "queryNorm"
        • value: 0.19178301
          description: "fieldWeight in 0, product of:"
          details:
          • value: 1.0
            description: "tf(freq=1.0), with freq of:"
            details:
            • value: 1.0
              description: "termFreq=1.0"
          • value: 0.30685282
            description: "idf(docFreq=1, maxDocs=1)"
          • value: 0.625
            description: "fieldNorm(doc=0)"
    • value: 0.13561107
      description: "weight(user:b in 0) [PerFieldSimilarity], result of:"
      details:
      • value: 0.13561107
        description: "score(doc=0,freq=1.0), product of:"
        details:
        • value: 0.70710677
          description: "queryWeight, product of:"
          details:
          • value: 0.30685282
            description: "idf(docFreq=1, maxDocs=1)"
          • value: 2.3043842
            description: "queryNorm"
        • value: 0.19178301
          description: "fieldWeight in 0, product of:"
          details:
          • value: 1.0
            description: "tf(freq=1.0), with freq of:"
            details:
            • value: 1.0
              description: "termFreq=1.0"
          • value: 0.30685282
            description: "idf(docFreq=1, maxDocs=1)"
          • value: 0.625
            description: "fieldNorm(doc=0)"
  • _shard: 3
    _node: "_baxQafwQ0WyAAZpyIv2ow"
    _index: "ttt"
    _type: "tweet"
    _id: "2"
    _score: 0.028130025
    _source:
    user: "b c"
    _explanation:
    value: 0.028130027
    description: "product of:"
    details:
    • value: 0.056260053
      description: "sum of:"
      details:
      • value: 0.056260053
        description: "weight(user:b in 0) [PerFieldSimilarity], result
        of:"
        details:
        • value: 0.056260053
          description: "score(doc=0,freq=1.0), product of:"
          details:
          • value: 0.29335263
            description: "queryWeight, product of:"
            details:
            • value: 0.30685282
              description: "idf(docFreq=1, maxDocs=1)"
            • value: 0.9560043
              description: "queryNorm"
          • value: 0.19178301
            description: "fieldWeight in 0, product of:"
            details:
            • value: 1.0
              description: "tf(freq=1.0), with freq of:"
              details:
              • value: 1.0
                description: "termFreq=1.0"
            • value: 0.30685282
              description: "idf(docFreq=1, maxDocs=1)"
            • value: 0.625
              description: "fieldNorm(doc=0)"
    • value: 0.5
      description: "coord(1/2)"

For the document, where only one term matches, the queryNorm is cca 2.5
times smaller than at document where both terms match. The result is too
much penalty for documents matching only one term.
I can see the same behaviour when using "bool" query with two "should"
clauses.

Is this a bug? Or what is the explanation of this behaviour? Where can I
find more info?

Thank you for help

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2

BTW - the reason I'm bothering with this is more complicated. Example in
the question is already simplified to the core. In my real scenario, I use
bool query composing more fuzzy queries. Then, the resulting score
penalizes some documents when only one field matches, which in that case
has more drastic impact to the user experience. For example exact match in
one field is far more scored than two fuzzy fields and so on. But the core
of the problem is the difference of queryNorm between documents which I
don't understand and cannot find the explanation among the Internet
resources.

Dne pátek 17. dubna 2015 15:00:40 UTC+2 Jakub Neubauer napsal(a):

Hi,
The ES guide states, that when computing score, "The same query
normalization factor is applied to every document" - viz
Lucene’s Practical Scoring Function | Elasticsearch: The Definitive Guide [master] | Elastic
But when I try this example:

curl -s -XDELETE 'localhost:9200/ttt'

curl -s -XPUT 'http://localhost:9200/ttt/tweet/1?refresh=true' -d '{
"user" : "a b"
}'
curl -s -XPUT 'http://localhost:9200/ttt/tweet/2?refresh=true' -d '{
"user" : "b c"
}'

curl -s -XGET 'localhost:9200/ttt/_search?explain=trye&format=yaml' -d '
{
"query": {
"match" : { "user" : "a b" }
}
}
'

I got this result - I highlighted the interesting parts:

took: 5
timed_out: false
_shards:
total: 5
successful: 5
failed: 0
hits:
total: 2
max_score: 0.2712221
hits:

  • _shard: 2
    _node: "_baxQafwQ0WyAAZpyIv2ow"
    _index: "ttt"
    _type: "tweet"
    _id: "1"
    _score: 0.2712221
    _source:
    user: "a b"
    _explanation:
    value: 0.27122214
    description: "sum of:"
    details:
    • value: 0.13561107
      description: "weight(user:a in 0) [PerFieldSimilarity], result of:"
      details:
      • value: 0.13561107
        description: "score(doc=0,freq=1.0), product of:"
        details:
        • value: 0.70710677
          description: "queryWeight, product of:"
          details:
          • value: 0.30685282
            description: "idf(docFreq=1, maxDocs=1)"
          • value: 2.3043842
            description: "queryNorm"
        • value: 0.19178301
          description: "fieldWeight in 0, product of:"
          details:
          • value: 1.0
            description: "tf(freq=1.0), with freq of:"
            details:
            • value: 1.0
              description: "termFreq=1.0"
          • value: 0.30685282
            description: "idf(docFreq=1, maxDocs=1)"
          • value: 0.625
            description: "fieldNorm(doc=0)"
    • value: 0.13561107
      description: "weight(user:b in 0) [PerFieldSimilarity], result of:"
      details:
      • value: 0.13561107
        description: "score(doc=0,freq=1.0), product of:"
        details:
        • value: 0.70710677
          description: "queryWeight, product of:"
          details:
          • value: 0.30685282
            description: "idf(docFreq=1, maxDocs=1)"
          • value: 2.3043842
            description: "queryNorm"
        • value: 0.19178301
          description: "fieldWeight in 0, product of:"
          details:
          • value: 1.0
            description: "tf(freq=1.0), with freq of:"
            details:
            • value: 1.0
              description: "termFreq=1.0"
          • value: 0.30685282
            description: "idf(docFreq=1, maxDocs=1)"
          • value: 0.625
            description: "fieldNorm(doc=0)"
  • _shard: 3
    _node: "_baxQafwQ0WyAAZpyIv2ow"
    _index: "ttt"
    _type: "tweet"
    _id: "2"
    _score: 0.028130025
    _source:
    user: "b c"
    _explanation:
    value: 0.028130027
    description: "product of:"
    details:
    • value: 0.056260053
      description: "sum of:"
      details:
      • value: 0.056260053
        description: "weight(user:b in 0) [PerFieldSimilarity], result
        of:"
        details:
        • value: 0.056260053
          description: "score(doc=0,freq=1.0), product of:"
          details:
          • value: 0.29335263
            description: "queryWeight, product of:"
            details:
            • value: 0.30685282
              description: "idf(docFreq=1, maxDocs=1)"
            • value: 0.9560043
              description: "queryNorm"
          • value: 0.19178301
            description: "fieldWeight in 0, product of:"
            details:
            • value: 1.0
              description: "tf(freq=1.0), with freq of:"
              details:
              • value: 1.0
                description: "termFreq=1.0"
            • value: 0.30685282
              description: "idf(docFreq=1, maxDocs=1)"
            • value: 0.625
              description: "fieldNorm(doc=0)"
    • value: 0.5
      description: "coord(1/2)"

For the document, where only one term matches, the queryNorm is cca 2.5
times smaller than at document where both terms match. The result is too
much penalty for documents matching only one term.
I can see the same behaviour when using "bool" query with two "should"
clauses.

Is this a bug? Or what is the explanation of this behaviour? Where can I
find more info?

Thank you for help

--
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3

Just some thoughts: As the queryNorm is calculated from terms frequencies -
it seems to me, that it is calculated from only those terms of the query
that somehow "matched" the document in some clause. So in our example, for
first document terms "a" and "b" were used to calculate queryNorm, but for
the second document only term "b". But this is not what one would suppose
from the documentation! I would expect that all query terms would be used
in calculation, to satisfy the statement that queryNorm is fixed for all
hits.

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