9.1 docs backports for 8.19 features (#132605)

Author: shainaraskas

docs/reference/index-modules.asciidoc

@@ -378,6 +378,10 @@ pipeline attempts to change the `_index` field, the indexing request will fail.
     per request through the use of the `expand_wildcards` parameter. Possible values are
     `true` and `false` (default).
 
+[[index-esql-stored-fields-sequential-proportion]] `index.esql.stored_fields_sequential_proportion`::
+
+    Tuning parameter for deciding when ES|QL will load <<search-fields-request,stored fields>> using a strategy tuned for loading dense sequence of documents. Allows values between 0.0 and 1.0 and defaults to 0.2. Indices with documents smaller than 10kb may see speed improvements loading `text` fields by setting this lower.
+
 [discrete]
 === Settings in other index modules
 

docs/reference/search/retriever.asciidoc

@@ -43,6 +43,9 @@ A <<text-similarity-reranker-retriever, retriever>> that enhances search results
 `rule`::
 A <<rule-retriever, retriever>> that applies contextual <<query-rules>> to pin or exclude documents for specific queries.
 
+`pinned`::
+A <<pinned-retriever, retriever>> that always places specified documents at the top of the results, with the remaining hits provided by a secondary retriever.
+
 [[standard-retriever]]
 ==== Standard Retriever
 
@@ -946,6 +949,60 @@ GET movies/_search
 <1> The `rule` retriever is the outermost retriever, applying rules to the search results that were previously reranked using the `rrf` retriever.
 <2> The `rrf` retriever returns results from all of its sub-retrievers, and the output of the `rrf` retriever is used as input to the `rule` retriever.
 
+[[pinned-retriever]]
+==== Pinned retriever
+
+A `pinned` retriever returns top documents by always placing specific documents at the top of the results, with the remaining hits provided by a secondary retriever. This retriever offers similar functionality to the <<query-dsl-pinned-query,pinned query>>, but works seamlessly with other retrievers. This is useful for promoting certain documents for particular queries, regardless of their relevance score.
+
+[discrete]
+[[retrievers-overview-pinned-retriever-parameters]]
+===== Parameters
+
+`ids`::
+(Optional, array of strings)
++
+A list of document IDs to pin at the top of the results, in the order provided.
+
+`docs`::
+(Optional, array of objects)
++
+List of objects specifying documents to pin. Each object must contain at least an `_id` field, and may also specify `_index` if pinning documents across multiple indices.
+
+`retriever`::
+(Optional, retriever object)
++
+A retriever (for example a `standard` retriever or a specialized retriever such as `rrf` retriever) used to retrieve the remaining documents after the pinned ones.
+
+Either `ids` or `docs` must be specified.
+
+[discrete]
+[[pinned-retriever-example]]
+==== Example: Pinned retriever using `docs
+
+[source,console]
+----
+GET /restaurants/_search
+{
+  "retriever": {
+    "pinned": {
+      "docs": [
+        { "_id": "doc1", "_index": "my-index" },
+        { "_id": "doc2" }
+      ],
+      "retriever": {
+        "standard": {
+          "query": {
+            "match": {
+              "title": "elasticsearch"
+            }
+          }
+        }
+      }
+    }
+  }
+}
+----
+
 [discrete]
 [[multi-field-query-format]]
 === Multi-field query format

docs/reference/search/search-your-data/retrievers-overview.asciidoc

@@ -69,30 +69,9 @@ Applies <<query-rules,query rules>> to the query before returning results.
 * <<text-similarity-reranker-retriever,*Text Similarity Re-ranker Retriever*>>.
 Used for <<semantic-reranking,semantic reranking>>.
 Requires first creating a `rerank` task using the <<put-inference-api,{es} Inference API>>.
-* <<retrievers-overview-pinned-retriever-parameters,*Pinned Retriever*>>.
+* <<pinned-retriever,*Pinned Retriever*>>.
 Returns top documents by always placing specific documents at the top of the results, with the remaining hits provided by a secondary retriever.
 
-[discrete]
-[[retrievers-overview-pinned-retriever-parameters]]
-==== Pinned Retriever Parameters
-
-`ids`::
-(Optional, array of strings)
-+
-A list of document IDs to pin at the top of the results, in the order provided.
-
-`docs`::
-(Optional, array of objects)
-+
-List of objects specifying documents to pin. Each object must contain at least an `_id` field, and may also specify `_index` if pinning documents across multiple indices.
-
-`retriever`::
-(Optional, retriever object)
-+
-A retriever (for example a `standard` retriever or a specialized retriever such as `rrf` retriever) used to retrieve the remaining documents after the pinned ones.
-
-Either `ids` or `docs` must be specified.
-
 [discrete]
 [[retrievers-overview-why-are-they-useful]]
 === What makes retrievers useful?