Multi-match query with filter condition differences between ES2.1.1 and ES.2.3.3

Elastic Stack Elasticsearch
1

Hi:
I am running into a problem with multi-match queries with filter conditions on ES 2.3.3. Its not returning the results I am expecting.
on ES 2.1.1 I get the results in the order I want but on ES 2.3.3. I do not.

Java - 1.8.0_45
Oracle linux 6.5

The mapping... :

{
"entity": {
    "properties": {
      "name": {
        "type": "string",
        "fields": {
          "na": {
            "index": "not_analyzed",
            "type": "string"
          },
          "autocomplete": {
            "analyzer": "autocomplete",
            "type": "string"
          }
        }
      },
  "type": {
    "index": "not_analyzed",
    "type": "string"
  }
}
}
}

My Query does a multi_match against the name field

{
  "query": {
    "bool": {
      "should": [
        {
          "bool": {
            "must": {
              "multi_match": {
                "query": "texas court of appeals, 1s",
                "fields": [
                  "name",
                  "name.na",
                  "name.autocomplete"
                ],
                "type": "best_fields"
              }
            },
            "filter": {
              "term": {
                "type": "date"
              }
            }
          }
        },
        {
          "bool": {
            "must": {
              "bool": {
                "must": {
                  "multi_match": {
                    "query": "texas court of appeals, 1s",
                    "fields": [
                      "name",
                      "name.na",
                      "name.autocomplete"
                    ],
                    "type": "best_fields"
                  }
                },
                "filter": {
                  "term": {
                    "type": "court"
                  }
                }
              }
            }
          }
        }
      ]
    }
  }
}

While I get the right document back in ES 2.1.1, on ES 2.3.3 I do not . and the matching document is not in top 10 or 20 documents.

If I remove the name.na field from the multi_match query, the query works like expected. If it is just one specific type (court) in the outermost bool query, the query returns the correct document.

So My question is :
Did the multi_match implementation change between versions 2.1.1 and 2.3.3 to cause this behavior ?

Any assistance is much appreciated.

Thanks

Ramdev

2

I'm not aware of any changes between those two versions, although that doesn't rule it out.

How many documents are in your index? How many shards? This may be a difference due to how the two versions physically placed the documents. Because scores are generated on a per-shard basis, the doc frequency (e.g. how many documents hold the term) are shard-local. When you only have a small number of documents, the placement on physical shards can often affect scoring simply because the shard-local DFs change.

You could try re-running your searches with dfs_query_then_fetch which does a pre-search to find all DFs so that scoring is "global".

Alternatively, perhaps run the explain api to see how/why each document matched, which may give you some clues.

3

Hi Zachary:
Thanks for the response. Here are the answers to some of the questions you asked :

  1. The index in both instances are in 1 Shard.
  2. There are about 1.7M docs in the index. It is a static index, meaning once docs are indexed, the index is no longer touched. (however, there is indexing going on on the Cluster)

Other than perhaps hardware differences, I am not seeing anything obvious with the setup. However, I will try out the explain API and see why docs are ranked differently. (and also the dfs_query_then_fetch - I am not sure it is affected if there is only 1 shard)

4

Ah, yeah, with only one shard you can ignore what I said about different DF's and dfs_query_then_fetch... since there is only one shard, everything is "global" for scoring purposes.

I think explain is the way to go from here, that should at least provide some details about how things are being scored.

5

This is dumbfounding.
So I just for kicks, tried submitting the query multiple times in rapid succession ( well, quickly, perhaps not rapid) using the sense UI. I found an odd behavior. The results flip flop. meaning every 3rd response is the right one, with a higher score.

I add a sort condition to the query to sort by _score (default being descending order) for deterministic results.

I can clearly see the score for the wrong result is lower than the right one.

Does this mean something ?

6

@polyfractal , a follow up question :

In an INdex (index) with a single Type (type), should a search :

index/_search VS index/type/_search yield different results ?

If it does return different results, how can I explain the behavior ?

Thanks

Ramdev

7

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