Multiterms on multi index

[Suresh_Ghatuwa]

Currently I am testing on ES Multi Terms feature. Please find the sample data with indices.

PUT multi_terms_test1
{
  "settings": {
    "number_of_shards": 1,
    "number_of_replicas": 0
  }
}

PUT multi_terms_test1/_mapping
{
  "properties": {
    "COUNTRY": {
      "type": "keyword"
    },
    "FIRST_NAME": {
      "type": "keyword"
    },
    "FULL_NAME": {
      "type": "keyword"
    },
    "PAY_DATE": {
      "type": "date",
      "format": "yyyy-MM-dd"
    },
    "SALARY": {
      "type": "long"
    },
    "ID": {
      "type": "keyword"
    }
  }
}

PUT multi_terms_test1/_doc/1
{
  "ID": "1",
  "COUNTRY": "USA",
  "FIRST_NAME": "John",
  "FULL_NAME":"John B",
  "PAY_DATE":"2022-02-15",
  "SALARY":1200
}

PUT multi_terms_test1/_doc/2
{
  "ID": "1",
  "COUNTRY": "Nepal",
  "FIRST_NAME": "Suresh",
  "FULL_NAME":"Suresh G",
  "PAY_DATE":"2022-12-31",
  "SALARY":1000
}

PUT multi_terms_test1/_doc/3
{
  "ID": "1",
  "COUNTRY": "France",
  "FIRST_NAME": "Michel",
  "FULL_NAME":"Michel J",
  "PAY_DATE":"2022-08-09",
  "SALARY":1500
}

PUT multi_terms_test2
{
  "settings": {
    "number_of_shards": 1,
    "number_of_replicas": 0
  }
}

POST _aliases
{
  "actions": [
    {
      "add": {
        "index": "multi_terms_test1",
        "alias": "multi_terms"
      }
    },
     {
      "add": {
        "index": "multi_terms_test2",
        "alias": "multi_terms"
      }
    }
  ]
}

Note:

• multi_terms_test1 is with mapping
• multi_terms_test2 is without mapping

From the above request, we had created multi_terms_test1 and multi_terms_test2 index pointing with multi_terms alias.

Now we are quering on alias (i.e. multi_terms) as shown below:

GET multi_terms/_search
{
  "size": 0,
  "aggs": {
    "country_pay_date": {
      "multi_terms": {
        "terms": [
          {
            "field": "COUNTRY"
          },
          {
            "field": "PAY_DATE"
          }
        ],
        "order": {
          "_key": "desc"
        },
        "size":7
      }
    }
  }
}

As multi_terms_test1 contains mapping but multi_terms_test2 doesnot contain mapping, we got following exception.

Exception:
Merging/Reducing the multi_term aggregations failed when computing the aggregation country_pay_date because the field in the position 2 in the aggregation has two different types in two different indices

But If i run the query on multi_terms_test1 index, we got the result as shown below:

{
  "took": 1,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": {
      "value": 3,
      "relation": "eq"
    },
    "max_score": null,
    "hits": []
  },
  "aggregations": {
    "country_pay_date": {
      "doc_count_error_upper_bound": 0,
      "sum_other_doc_count": 0,
      "buckets": [
        {
          "key": [
            "USA",
            "2022-02-15"
          ],
          "key_as_string": "USA|2022-02-15",
          "doc_count": 1
        }
      ]
    }
  }
}

And executing on multi_terms_test2 index result empty result as shown below:

{
  "took": 1,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": {
      "value": 0,
      "relation": "eq"
    },
    "max_score": null,
    "hits": []
  },
  "aggregations": {
    "country_pay_date": {
      "doc_count_error_upper_bound": 0,
      "sum_other_doc_count": 0,
      "buckets": []
    }
  }
}

Question:

• Do we need to have mapping in all index for multi terms?
• Why multi terms works on quering single index without mapping one?
• Is there any other parameter (like ignore_unmapped) need to be added in ES Query?

OR
Is this known issue in Elasticsearch itself?

Tested ES Version: 7.16 and 8.6
Thank you inadvance.