opensearch-project · natebower · Oct 7, 2025 · Sep 23, 2025 · Oct 2, 2025 · Oct 6, 2025
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 title: Collapse
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-parent: Search processors
+parent: User-defined search processors
 grand_parent: Search pipelines
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 title: Hybrid score explanation
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-parent: Search processors
+parent: User-defined search processors
 grand_parent: Search pipelines
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 title: Filter query
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-parent: Search processors
+parent: User-defined search processors
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@@ -10,27 +10,22 @@
 
 # Search pipelines
 
-You can use _search pipelines_ to build new or reuse existing result rerankers, query rewriters, and other components that operate on queries or results. Search pipelines make it easier for you to process search queries and search results within OpenSearch. Moving some of your application functionality into an OpenSearch search pipeline reduces the overall complexity of your application. As part of a search pipeline, you specify a list of processors that perform modular tasks. You can then easily add or reorder these processors to customize search results for your application. 
+You can use _search pipelines_ to build new or reuse existing result rerankers, query rewriters, and other components that operate on queries or results. Search pipelines make it easier for you to process search queries and search results within OpenSearch. Moving some of your application functionality into an OpenSearch search pipeline reduces the overall complexity of your application. As part of a search pipeline, you specify a list of search processors that perform modular tasks. You can then easily add or reorder these processors to customize search results for your application. 
 
-## Terminology
-
-The following is a list of search pipeline terminology:
-
-* [_Search request processor_]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/search-processors#search-request-processors): A component that intercepts a search request (the query and the metadata passed in the request), performs an operation with or on the search request, and returns the search request.
-* [_Search response processor_]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/search-processors#search-response-processors): A component that intercepts a search response and search request (the query, results, and metadata passed in the request), performs an operation with or on the search response, and returns the search response.
-* [_Search phase results processor_]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/search-processors#search-phase-results-processors): A component that runs between search phases at the coordinating node level. A search phase results processor intercepts the results retrieved from one search phase and transforms them before passing them to the next search phase.
-* [_Processor_]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/search-processors/): Either a search request processor or a search response processor.
-* _Search pipeline_: An ordered list of processors that is integrated into OpenSearch. The pipeline intercepts a query, performs processing on the query, sends it to OpenSearch, intercepts the results, performs processing on the results, and returns them to the calling application, as shown in the following diagram. 
+When defined, a search pipeline is an ordered list of search processors that is integrated into OpenSearch. The pipeline shown in the following diagram intercepts a query, performs processing on the query, sends it to OpenSearch, intercepts the results, performs processing on the results, and returns them to the calling application.
 
 ![Search processor diagram]({{site.url}}{{site.baseurl}}/images/search-pipelines.png)
 
 Both request and response processing for the pipeline are performed on the coordinator node, so there is no shard-level processing.
 {: .note}
 
-## Processors
+## Search processors
 
-To learn more about available search processors, see [Search processors]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/search-processors/).
+Search processors can be classified by **execution phase** (when they run):
 
+- [Search request processors]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/search-processors#search-request-processors): A _search request processor_ intercepts a search request (the query and the metadata passed in the request), performs an operation with or on the search request, and submits the search request to the index.
+- [Search response processors]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/search-processors#search-response-processors): A _search response processor_ intercepts a search response and search request (the query, results, and metadata passed in the request), performs an operation with or on the search response, and returns the search response.
+- [Search phase results processors]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/search-processors#search-phase-results-processors): A _search phase results processor_ runs between search phases at the coordinating node level. It intercepts the results retrieved from one search phase and transforms them before passing them to the next search phase.
 
 ## Example
 
@@ -77,6 +72,12 @@
 
 To learn about retrieving details for an existing search pipeline, see [Retrieving search pipelines]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/retrieving-search-pipeline/).
 
+## Manual and automatic processor creation
+
+Search processors can be created manually or automatically:
+
+- [User-defined processors]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/search-processors): Processors configured manually in search pipelines, like in the preceding [example](#example).
+- [System-generated processors]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/system-generated-search-processors/): Processors automatically created by OpenSearch based on search request parameters.
 
 ## Search pipeline metrics
 

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 title: ML inference (request)
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+parent: User-defined search processors
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 title: ML inference (response) 
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+parent: User-defined search processors
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 title: Neural query enricher
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+parent: User-defined search processors
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 layout: default
 title: Neural sparse query two-phase
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 title: Normalization
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 title: Oversample
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-parent: Search processors
+parent: User-defined search processors
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 title: Personalize search ranking
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-parent: Search processors
+parent: User-defined search processors
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 title: Retrieval-augmented generation
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 title: Rerank
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+parent: User-defined search processors
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 layout: default
 title: Score ranker
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+parent: User-defined search processors
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 title: Script
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+parent: User-defined search processors
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@@ -1,7 +1,7 @@
 ---
 layout: default
 title: Search pipeline metrics
-nav_order: 50
+nav_order: 60
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 parent: Search pipelines
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@@ -1,22 +1,20 @@
 ---
 layout: default
-title: Search processors
+title: User-defined search processors
 nav_order: 40
 has_children: true
 parent: Search pipelines
 ---
 
-# Search processors
+# User-defined search processors
 
-Search processors can be of the following types:
+**User-defined search processors** are processors that you manually configure in search pipelines to customize search behavior. You define these processors in your pipeline configuration and control their parameters, execution order, and conditions.
 
-- [Search request processors](#search-request-processors)
-- [Search response processors](#search-response-processors)
-- [Search phase results processors](#search-phase-results-processors)
+The following sections list all user-defined search processors available in OpenSearch. OpenSearch can also create processors automatically based on search request parameters. For more information, see [System-generated search processors]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/system-generated-search-processors/).
 
 ## Search request processors
 
-A search request processor intercepts a search request (the query and the metadata passed in the request), performs an operation with or on the search request, and submits the search request to the index.
+A _search request processor_ intercepts a search request (the query and the metadata passed in the request), performs an operation with or on the search request, and submits the search request to the index.
 
 The following table lists all supported search request processors.
 
@@ -31,7 +29,7 @@ Processor | Description | Earliest available version
 
 ## Search response processors
 
-A search response processor intercepts a search response and search request (the query, results, and metadata passed in the request), performs an operation with or on the search response, and returns the search response.
+A _search response processor_ intercepts a search response and search request (the query, results, and metadata passed in the request), performs an operation with or on the search response, and returns the search response.
 
 The following table lists all supported search response processors.
 
@@ -48,10 +46,9 @@ Processor | Description | Earliest available version
 [`split`]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/split-processor/)| Splits a string field into an array of substrings based on a specified delimiter. | 2.17
 [`truncate_hits`]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/truncate-hits-processor/)| Discards search hits after a specified target count is reached. Can undo the effect of the `oversample` request processor.  | 2.12
 
-
 ## Search phase results processors
 
-A search phase results processor runs between search phases at the coordinating node level. It intercepts the results retrieved from one search phase and transforms them before passing them to the next search phase.
+A _search phase results processor_ runs between search phases at the coordinating node level. It intercepts the results retrieved from one search phase and transforms them before passing them to the next search phase.
 
 The following table lists all supported search phase results processors.
 

@@ -3,7 +3,7 @@ layout: default
 title: Sort
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-parent: Search processors
+parent: User-defined search processors
 grand_parent: Search pipelines
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@@ -3,7 +3,7 @@ layout: default
 title: Split
 nav_order: 140
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-parent: Search processors
+parent: User-defined search processors
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@@ -0,0 +1,66 @@
+---
+layout: default
+title: System-generated search processors
+nav_order: 50
+has_children: false
+parent: Search pipelines
+---
+
+# System-generated search processors
+**Introduced 3.3**
+{: .label .label-purple }
+
+System-generated search processors are processors that OpenSearch creates automatically based on the search request. Unlike [user-defined processors]({{site.url}}{{site.baseurl}}/search-plugins/search-pipelines/search-processors/) that you manually configure in pipelines, system-generated processors are triggered automatically when certain features are used, eliminating the need for manual processor configuration.
+
+## Enabling system-generated search processors
+
+To enable system-generated search processor creation, set the `cluster.search.enabled_system_generated_factories` cluster setting to `*` (all factories) or explicitly list the factories you want to enable. The following example enables `mmr_over_sample_factory` and `mmr_rerank_factory`:
+
+```json
+PUT _cluster/settings
+{
+  "persistent": {
+    "cluster.search.enabled_system_generated_factories": [
+      "mmr_over_sample_factory",
+      "mmr_rerank_factory"
+    ]
+  }
+}
+```
+{% include copy-curl.html %}
+
+## Processor types
+
+OpenSearch supports the following types of system-generated processors:
+
+* [Search request processors](#system-generated-search-request-processors)
+* [Search response processors](#system-generated-search-response-processors)
+
+Each system-generated processor runs at a fixed execution stage, either before or after user-defined processors of the same type.
+{: .note}
+
+### System-generated search request processors
+
+The following table lists the available system-generated search request processors.
+
+| Processor name    | Processor factory name    | Execution stage     | Trigger condition                                          | Description                                                                                                                                         |
+| ----------------- | ------------------------- | ------------------- | ---------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `mmr_over_sample` | `mmr_over_sample_factory` | Runs after any user-defined request processors. | Triggered when a search request includes the `mmr` parameter in the `ext` object. See [Vector search with MMR reranking]({{site.url}}{{site.baseurl}}/vector-search/specialized-operations/vector-search-mmr/). | Adjusts the query size and `k` value of the `knn` or `neural` query to oversample candidates for maximal marginal relevance (MMR) reranking. |
+
+### System-generated search response processors
+
+The following table lists the available system-generated search response processors.
+
+| Processor name | Processor factory name | Execution stage    | Trigger condition                                          | Description                                                                                                                               |
+| -------------- | ---------------------- | ------------------ | ---------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------- |
+| `mmr_rerank`   | `mmr_rerank_factory`   | Runs before any user-defined response processors. | Triggered when a search request includes the `mmr` parameter in the `ext` object. See [Vector search with MMR reranking]({{site.url}}{{site.baseurl}}/vector-search/specialized-operations/vector-search-mmr/). | Reranks the oversampled results using MMR and reduces them to the original query size.  |
+
+## Limitations
+
+The following limitations apply to system-generated processors:
+
+- OpenSearch supports only **one system-generated processor per processor type and execution stage** for a given search request. Since each processor type (request and response) can run at two execution stages (before or after user-defined processors), a single search request can include multiple system-generated processors, as long as they are of different types or run at different execution stages. This limitation ensures deterministic execution order and predictable behavior.
+
+## Related pages
+
+- [Vector search with MMR reranking]({{site.url}}{{site.baseurl}}/vector-search/specialized-operations/vector-search-mmr/)
@@ -3,7 +3,7 @@ layout: default
 title: Truncate hits
 nav_order: 150
 has_children: false
-parent: Search processors
+parent: User-defined search processors
 grand_parent: Search pipelines
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@@ -13,6 +13,9 @@ cards:
   - heading: "Radial search"
     description: "Search all points in a vector space that reside within a specified maximum distance or minimum score threshold from a query point"
     link: "/vector-search/specialized-operations/radial-search-knn/"
+  - heading: "Vector search with MMR reranking"
+    description: "Improve vector search results by automatically reranking for both relevance and diversity using maximal marginal relevance (MMR)"
+    link: "/vector-search/specialized-operations/vector-search-mmr/"
 ---
 
 # Specialized vector search