Constant Expression Script Score Returns Two Different Results for Different Queries

Elastic Stack Elasticsearch
1

Hi all :slight_smile:

Using Elasticsearch 6.8.1 I'm seeing some very strange behavior with script_score. Using either expression or painless lang, the script "42" which should be a constant expression in either language that evaluates the same value for every document every time, is giving me two different results, even for the same document, when used to score a different query.

$ cat ~/audit.sh
#!/bin/bash

function search() {
  curl -sS -X POST 'http://10.101.0.1:20400/saas/_search?pretty' -H content-type:application/json -d "$1"
}

search '{
  "size": 1,
  "_source": false,
  "query": {
    "function_score": {
      "script_score": {
        "script": {
          "lang": "expression",
          "source": "42"
        }
      },
      "query": {
        "bool": {
          "filter": [
            {
              "exists": {
                "field": "social_account.customer_codes"
              }
            }
          ]
        }
      }
    }
  }
}'

search '{
  "size": 1,
  "_source": false,
  "query": {
    "function_score": {
      "script_score": {
        "script": {
          "lang": "expression",
          "source": "42"
        }
      },
      "query": {
        "term": {
          "_id" : "a903c3a5-32f5-45ba-b092-3a80dc4e965a"
        }
      }
    }
  }
}'
$ ~/audit.sh
{
  "took" : 31,
  "timed_out" : false,
  "_shards" : {
    "total" : 10,
    "successful" : 10,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 441988,
    "max_score" : 0.0,
    "hits" : [
      {
        "_index" : "saas-data-2",
        "_type" : "_doc",
        "_id" : "a903c3a5-32f5-45ba-b092-3a80dc4e965a",
        "_score" : 0.0
      }
    ]
  }
}
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 10,
    "successful" : 10,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 1,
    "max_score" : 42.0,
    "hits" : [
      {
        "_index" : "saas-data-2",
        "_type" : "_doc",
        "_id" : "a903c3a5-32f5-45ba-b092-3a80dc4e965a",
        "_score" : 42.0
      }
    ]
  }
}

I'm unsure why the score would be 42.0 in some cases and 0.0 in another, even on the same document.

Thanks in advance

2

I've solved the issue.

It turns out that function_score has a boost_mode parameter that is set by default to product and according to the _explain, the score contribution for the queryexists is 0.0 while for the term query it is 1.0 because the former is run in a filter context.

{
  "_index" : "saas-data-2",
  "_type" : "_doc",
  "_id" : "a903c3a5-32f5-45ba-b092-3a80dc4e965a",
  "matched" : true,
  "explanation" : {
    "value" : 0.0,
    "description" : "sum of:",
    "details" : [
      {
        "value" : 0.0,
        "description" : "function score, product of:",
        "details" : [
          {
            "value" : 0.0,
            "description" : "ConstantScore(DocValuesFieldExistsQuery [field=social_account.customer_codes])^0.0",
            "details" : [ ]
          },
          {
            "value" : 42.0,
            "description" : "min of:",
            "details" : [
              {
                "value" : 42.0,
                "description" : "script score function, computed with script:\"Script{type=inline, lang='expression', idOrCode='42', options={}, params={}}\" and parameters: \n{}",
                "details" : [
                  {
                    "value" : 0.0,
                    "description" : "_score: ",
                    "details" : [
                      {
                        "value" : 0.0,
                        "description" : "ConstantScore(DocValuesFieldExistsQuery [field=social_account.customer_codes])^0.0",
                        "details" : [ ]
                      }
                    ]
                  }
                ]
              },
              {
                "value" : 3.4028235E38,
                "description" : "maxBoost",
                "details" : [ ]
              }
            ]
          }
        ]
      },
      {
        "value" : 0.0,
        "description" : "match on required clause, product of:",
        "details" : [
          {
            "value" : 0.0,
            "description" : "# clause",
            "details" : [ ]
          },
          {
            "value" : 1.0,
            "description" : "DocValuesFieldExistsQuery [field=_primary_term]",
            "details" : [ ]
          }
        ]
      }
    ]
  }
}

versus:

{
  "_index" : "saas-data-2",
  "_type" : "_doc",
  "_id" : "a903c3a5-32f5-45ba-b092-3a80dc4e965a",
  "matched" : true,
  "explanation" : {
    "value" : 42.0,
    "description" : "sum of:",
    "details" : [
      {
        "value" : 42.0,
        "description" : "function score, product of:",
        "details" : [
          {
            "value" : 1.0,
            "description" : "ConstantScore(_id:[6b dd 37 73 76 b9 fb 7d 9f e7 ee 39 6d af 9b d3 dd be dd af 34 75 ce 1e f7 ae 5a])",
            "details" : [ ]
          },
          {
            "value" : 42.0,
            "description" : "min of:",
            "details" : [
              {
                "value" : 42.0,
                "description" : "script score function, computed with script:\"Script{type=inline, lang='expression', idOrCode='42', options={}, params={}}\" and parameters: \n{}",
                "details" : [
                  {
                    "value" : 1.0,
                    "description" : "_score: ",
                    "details" : [
                      {
                        "value" : 1.0,
                        "description" : "ConstantScore(_id:[6b dd 37 73 76 b9 fb 7d 9f e7 ee 39 6d af 9b d3 dd be dd af 34 75 ce 1e f7 ae 5a])",
                        "details" : [ ]
                      }
                    ]
                  }
                ]
              },
              {
                "value" : 3.4028235E38,
                "description" : "maxBoost",
                "details" : [ ]
              }
            ]
          }
        ]
      },
      {
        "value" : 0.0,
        "description" : "match on required clause, product of:",
        "details" : [
          {
            "value" : 0.0,
            "description" : "# clause",
            "details" : [ ]
          },
          {
            "value" : 1.0,
            "description" : "DocValuesFieldExistsQuery [field=_primary_term]",
            "details" : [ ]
          }
        ]
      }
    ]
  }
}
3

So it turns out that 6.5.3 and 6.8.1 behave differently. The results above are from 6.8.1 but in 6.5.3, both queries score the document the same way.

I believe 6.5.3 has a bug that has been fixed in 6.8.1 that hasn't been backported to 6.5.

Is 6.5 still receiving fixes or no?

Thanks!

4

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