Wrong document score of nested knn query

AlexanderOtt85 commented 3 weeks ago

Elasticsearch Version

8.14.1

Installed Plugins

No response

Java Version

bundled

OS Version

docker-image = docker.elastic.co/elasticsearch/elasticsearch:8.14.1

Problem Description

For a nested knn query with score_mode = max the document score does not match the expected score. I would expect the document score = 0.5852207 which is the maximum score of the inner hit (see 'nested knn query' in '_elasticsearch_8_14_1_knn_queryscore.txt').

For a nested query string query however the document score is the maximum score of the inner hit (see '_nested querystring query' in '_elasticsearch_8_14_1_knn_queryscore.txt').

Steps to Reproduce

elasticsearch_8_14_1_knn_query_score.txt

Logs (if relevant)

No response

elasticsearchmachine commented 3 weeks ago

Pinging @elastic/es-search (Team:Search)

elasticsearchmachine commented 2 weeks ago

Pinging @elastic/es-search-relevance (Team:Search Relevance)

benwtrent commented 2 weeks ago

The default for nested vector is indeed max and that is the only score mode supported. However other nested queries can support other modes. See the docs: https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-nested-query.html#nested-top-level-params

The default is avg for all queries other than knn.

Could you provide data and minimal steps for replication?

Is the scoring just weird in the explain or is it the actual _score of the doc?

AlexanderOtt85 commented 2 weeks ago

The actual _score of the doc is incorrect. It should be possible to reproduce with the requests in https://github.com/user-attachments/files/16048978/elasticsearch_8_14_1_knn_query_score.txt

benwtrent commented 2 weeks ago

@AlexanderOtt85 Those queries are exceptionally complex and don't contain any test data nor the responses that were returned.

All the testing I have done shows that scoring is working just fine.

Could you provide the responses for your queries? Possibly some test data that replicates the issue?

AlexanderOtt85 commented 1 week ago

Sorry. The attachment now contains 4 requests (search for ###).

Create index
Index document
knnQuery where the score is not OK. expected score = 0.5852207 current score = 0.5711336
queryStringQuery where the score is OK. expected score = 1.2144799 current score = 1.2144799

elasticsearch_8_14_1_knn_query_score.txt

benwtrent commented 1 week ago

@AlexanderOtt85

I used the doc in your payload and indexed it and got the following:

"_score": 0.5852207,

"_explanation": {
                    "value": 0.5852207,
                    "description": "Score based on 1 child docs in range from 0 to 377, using score mode Max",
                    "details": [...]

            "inner_hits": {
                    "du.medium.keyframe_tc_hit": {
                        "hits": {
                            "total": {
                                "value": 352,
                                "relation": "eq"
                            },
                            "max_score": 0.5852207,

                            "hits": [
                                {
                                    "_index": "my_index",
                                    "_id": "YmkkuJABEnKFO-LMzsrO",
                                    "_nested": {
                                        "field": "du",
                                        "offset": 1,
                                        "_nested": {
                                            "field": "medium",
                                            "offset": 1,
                                            "_nested": {
                                                "field": "keyframe_tc_hit",
                                                "offset": 8
                                            }
                                        }
                                    },
                                    "_score": 0.5852207
                                },

Everything checks out.

What hardware are you testing this on?

Is it a single node cluster?

benwtrent commented 1 week ago

@AlexanderOtt85 I figured out whats going on while fall asleep. A good night's sleep is the best debugger.

This indeed is a bug, and it is fixed in 8.15 (this is why I didn't see it when I tested).

It surfaces in the following scenario:

The new default index type in 8.14 is int8_hnsw, this will automatically quantize vectors and use the quantized vectors for scoring
When a nested query gets more than one inner hit for vectors, it must rescore them (done later, after the initial search process). In 8.14, nested queries did this with the RAW float32 vectors, not the int8_hnsw ones. Consequently, scores can be slightly different between them.
In 8.15, we corrected this by using the quantized scoring when providing the inner scores for the inner hits.

So, to fix your particular weird scenario, the answer is:

upgrade to 8.15 when its out
manually set the index_options: {type: "hnsw"} in your mapping. Note, this requires 4x as much ram.

Sorry for the inconsistency here!

AlexanderOtt85 commented 1 week ago

@benwtrent thanks for the clarification. I also get the expected score of _score": 0.5852207 with index_options: {type: "hnsw"} and 8.14.2

I think we will wait for 8.15... when can we expect a release 8.15

benwtrent commented 1 week ago

@AlexanderOtt85 8.15 release will be the next one. No public date is set.

elastic / elasticsearch