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Add a generic rescorer retriever based on the search request's resc…
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…ore functionality (elastic#118585)

This pull request introduces a new retriever called `rescorer`, which leverages the `rescore` functionality of the search request.  
The `rescorer` retriever re-scores only the top documents retrieved by its child retriever, offering fine-tuned scoring capabilities.  

All rescorers supported in the `rescore` section of a search request are available in this retriever, and the same format is used to define the rescore configuration.  

<details>
<summary>Example:</summary>

```yaml
  - do:
      search:
        index: test
        body:
          retriever:
            rescorer:
              rescore:
                window_size: 10
                query:
                  rescore_query:
                    rank_feature:
                      field: "features.second_stage"
                      linear: { }
                  query_weight: 0
              retriever:
                standard:
                  query:
                    rank_feature:
                      field: "features.first_stage"
                      linear: { }
          size: 2
```

</details>

Closes elastic#118327

Co-authored-by: Liam Thompson <[email protected]>
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@jimczi @leemthompo
jimczi and leemthompo committed Dec 18, 2024
1 parent 3d1f8d2 commit b589cce
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7 changes: 7 additions & 0 deletions docs/changelog/118585.yaml
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pr: 118585
summary: Add a generic `rescorer` retriever based on the search request's rescore
functionality
area: Ranking
type: feature
issues:
- 118327
121 changes: 120 additions & 1 deletion docs/reference/search/retriever.asciidoc
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Expand Up @@ -22,6 +22,9 @@ A <<standard-retriever, retriever>> that replaces the functionality of a traditi
`knn`::
A <<knn-retriever, retriever>> that replaces the functionality of a <<search-api-knn, knn search>>.

`rescorer`::
A <<rescorer-retriever, retriever>> that replaces the functionality of the <<rescore, query rescorer>>.

`rrf`::
A <<rrf-retriever, retriever>> that produces top documents from <<rrf, reciprocal rank fusion (RRF)>>.

Expand Down Expand Up @@ -371,6 +374,122 @@ GET movies/_search
----
// TEST[skip:uses ELSER]

[[rescorer-retriever]]
==== Rescorer Retriever

The `rescorer` retriever re-scores only the results produced by its child retriever.
For the `standard` and `knn` retrievers, the `window_size` parameter specifies the number of documents examined per shard.

For compound retrievers like `rrf`, the `window_size` parameter defines the total number of documents examined globally.

When using the `rescorer`, an error is returned if the following conditions are not met:

* The minimum configured rescore's `window_size` is:
** Greater than or equal to the `size` of the parent retriever for nested `rescorer` setups.
** Greater than or equal to the `size` of the search request when used as the primary retriever in the tree.

* And the maximum rescore's `window_size` is:
** Smaller than or equal to the `size` or `rank_window_size` of the child retriever.

[discrete]
[[rescorer-retriever-parameters]]
===== Parameters

`rescore`::
(Required. <<rescore, A rescorer definition or an array of rescorer definitions>>)
+
Defines the <<rescore, rescorers>> applied sequentially to the top documents returned by the child retriever.

`retriever`::
(Required. <<retriever, retriever>>)
+
Specifies the child retriever responsible for generating the initial set of top documents to be re-ranked.

`filter`::
(Optional. <<query-dsl, query object or list of query objects>>)
+
Applies a <<query-dsl-bool-query, boolean query filter>> to the retriever, ensuring that all documents match the filter criteria without affecting their scores.

[discrete]
[[rescorer-retriever-example]]
==== Example

The `rescorer` retriever can be placed at any level within the retriever tree.
The following example demonstrates a `rescorer` applied to the results produced by an `rrf` retriever:

[source,console]
----
GET movies/_search
{
"size": 10, <1>
"retriever": {
"rescorer": { <2>
"rescore": {
"query": { <3>
"window_size": 50, <4>
"rescore_query": {
"script_score": {
"script": {
"source": "cosineSimilarity(params.queryVector, 'product-vector_final_stage') + 1.0",
"params": {
"queryVector": [-0.5, 90.0, -10, 14.8, -156.0]
}
}
}
}
}
},
"retriever": { <5>
"rrf": {
"rank_window_size": 100, <6>
"retrievers": [
{
"standard": {
"query": {
"sparse_vector": {
"field": "plot_embedding",
"inference_id": "my-elser-model",
"query": "films that explore psychological depths"
}
}
}
},
{
"standard": {
"query": {
"multi_match": {
"query": "crime",
"fields": [
"plot",
"title"
]
}
}
}
},
{
"knn": {
"field": "vector",
"query_vector": [10, 22, 77],
"k": 10,
"num_candidates": 10
}
}
]
}
}
}
}
}
----
// TEST[skip:uses ELSER]
<1> Specifies the number of top documents to return in the final response.
<2> A `rescorer` retriever applied as the final step.
<3> The definition of the `query` rescorer.
<4> Defines the number of documents to rescore from the child retriever.
<5> Specifies the child retriever definition.
<6> Defines the number of documents returned by the `rrf` retriever, which limits the available documents to

[[text-similarity-reranker-retriever]]
==== Text Similarity Re-ranker Retriever

Expand Down Expand Up @@ -772,4 +891,4 @@ When a retriever is specified as part of a search, the following elements are no
* <<search-after, `search_after`>>
* <<request-body-search-terminate-after, `terminate_after`>>
* <<search-sort-param, `sort`>>
* <<rescore, `rescore`>>
* <<rescore, `rescore`>> use a <<rescorer-retriever, rescorer retriever>> instead
1 change: 1 addition & 0 deletions rest-api-spec/build.gradle
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Expand Up @@ -258,4 +258,5 @@ tasks.named("yamlRestTestV7CompatTransform").configure({ task ->
task.skipTest("search.vectors/41_knn_search_bbq_hnsw/Test knn search", "Scoring has changed in latest versions")
task.skipTest("search.vectors/42_knn_search_bbq_flat/Test knn search", "Scoring has changed in latest versions")
task.skipTest("synonyms/90_synonyms_reloading_for_synset/Reload analyzers for specific synonym set", "Can't work until auto-expand replicas is 0-1 for synonyms index")
task.skipTest("search/90_search_after/_shard_doc sort", "restriction has been lifted in latest versions")
})
225 changes: 225 additions & 0 deletions ...src/yamlRestTest/resources/rest-api-spec/test/search.retrievers/30_rescorer_retriever.yml
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setup:
- requires:
cluster_features: [ "search.retriever.rescorer.enabled" ]
reason: "Support for rescorer retriever"

- do:
indices.create:
index: test
body:
settings:
number_of_shards: 1
number_of_replicas: 0
mappings:
properties:
available:
type: boolean
features:
type: rank_features

- do:
bulk:
refresh: true
index: test
body:
- '{"index": {"_id": 1 }}'
- '{"features": { "first_stage": 1, "second_stage": 10}, "available": true, "group": 1}'
- '{"index": {"_id": 2 }}'
- '{"features": { "first_stage": 2, "second_stage": 9}, "available": false, "group": 1}'
- '{"index": {"_id": 3 }}'
- '{"features": { "first_stage": 3, "second_stage": 8}, "available": false, "group": 3}'
- '{"index": {"_id": 4 }}'
- '{"features": { "first_stage": 4, "second_stage": 7}, "available": true, "group": 1}'
- '{"index": {"_id": 5 }}'
- '{"features": { "first_stage": 5, "second_stage": 6}, "available": true, "group": 3}'
- '{"index": {"_id": 6 }}'
- '{"features": { "first_stage": 6, "second_stage": 5}, "available": false, "group": 2}'
- '{"index": {"_id": 7 }}'
- '{"features": { "first_stage": 7, "second_stage": 4}, "available": true, "group": 3}'
- '{"index": {"_id": 8 }}'
- '{"features": { "first_stage": 8, "second_stage": 3}, "available": true, "group": 1}'
- '{"index": {"_id": 9 }}'
- '{"features": { "first_stage": 9, "second_stage": 2}, "available": true, "group": 2}'
- '{"index": {"_id": 10 }}'
- '{"features": { "first_stage": 10, "second_stage": 1}, "available": false, "group": 1}'

---
"Rescorer retriever basic":
- do:
search:
index: test
body:
retriever:
rescorer:
rescore:
window_size: 10
query:
rescore_query:
rank_feature:
field: "features.second_stage"
linear: { }
query_weight: 0
retriever:
standard:
query:
rank_feature:
field: "features.first_stage"
linear: { }
size: 2

- match: { hits.total.value: 10 }
- match: { hits.hits.0._id: "1" }
- match: { hits.hits.0._score: 10.0 }
- match: { hits.hits.1._id: "2" }
- match: { hits.hits.1._score: 9.0 }

- do:
search:
index: test
body:
retriever:
rescorer:
rescore:
window_size: 3
query:
rescore_query:
rank_feature:
field: "features.second_stage"
linear: {}
query_weight: 0
retriever:
standard:
query:
rank_feature:
field: "features.first_stage"
linear: {}
size: 2

- match: {hits.total.value: 10}
- match: {hits.hits.0._id: "8"}
- match: { hits.hits.0._score: 3.0 }
- match: {hits.hits.1._id: "9"}
- match: { hits.hits.1._score: 2.0 }

---
"Rescorer retriever with pre-filters":
- do:
search:
index: test
body:
retriever:
rescorer:
filter:
match:
available: true
rescore:
window_size: 10
query:
rescore_query:
rank_feature:
field: "features.second_stage"
linear: { }
query_weight: 0
retriever:
standard:
query:
rank_feature:
field: "features.first_stage"
linear: { }
size: 2

- match: { hits.total.value: 6 }
- match: { hits.hits.0._id: "1" }
- match: { hits.hits.0._score: 10.0 }
- match: { hits.hits.1._id: "4" }
- match: { hits.hits.1._score: 7.0 }

- do:
search:
index: test
body:
retriever:
rescorer:
rescore:
window_size: 4
query:
rescore_query:
rank_feature:
field: "features.second_stage"
linear: { }
query_weight: 0
retriever:
standard:
filter:
match:
available: true
query:
rank_feature:
field: "features.first_stage"
linear: { }
size: 2

- match: { hits.total.value: 6 }
- match: { hits.hits.0._id: "5" }
- match: { hits.hits.0._score: 6.0 }
- match: { hits.hits.1._id: "7" }
- match: { hits.hits.1._score: 4.0 }

---
"Rescorer retriever and collapsing":
- do:
search:
index: test
body:
retriever:
rescorer:
rescore:
window_size: 10
query:
rescore_query:
rank_feature:
field: "features.second_stage"
linear: { }
query_weight: 0
retriever:
standard:
query:
rank_feature:
field: "features.first_stage"
linear: { }
collapse:
field: group
size: 3

- match: { hits.total.value: 10 }
- match: { hits.hits.0._id: "1" }
- match: { hits.hits.0._score: 10.0 }
- match: { hits.hits.1._id: "3" }
- match: { hits.hits.1._score: 8.0 }
- match: { hits.hits.2._id: "6" }
- match: { hits.hits.2._score: 5.0 }

---
"Rescorer retriever and invalid window size":
- do:
catch: "/\\[rescorer\\] requires \\[window_size: 5\\] be greater than or equal to \\[size: 10\\]/"
search:
index: test
body:
retriever:
rescorer:
rescore:
window_size: 5
query:
rescore_query:
rank_feature:
field: "features.second_stage"
linear: { }
query_weight: 0
retriever:
standard:
query:
rank_feature:
field: "features.first_stage"
linear: { }
size: 10
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