adding index prefix mapping parameter documentation

_field-types/mapping-parameters/index-prefixes.md

@@ -0,0 +1,112 @@
+---
+layout: default
+title: Index prefixes
+parent: Mapping parameters
+grand_parent: Mapping and field types
+nav_order: 90
+has_children: false
+has_toc: false
+---
+
+# Index prefixes
+
+The `index_prefixes` mapping parameter instructs the engine to generate additional index entries for the beginning segments of terms in a text field. When enabled, it builds a prefix index based on configurable minimum and maximum character lengths. This can significantly improve the performance of prefix queries, such as autocomplete or search-as-you-type, by allowing these queries to quickly match the pre-indexed term prefixes.
+
+By default, prefix indexing is not performed, keeping the index size minimal and indexing operations fast. However, if your application benefits from rapid prefix matching, enabling this parameter can provide a marked improvement in query efficiency.
+
+## Index prefixes configuration
+
+Following configuration can be passed to `index_prefixes` mapping parameter:
+
+- `min_chars`: Minimum length of the prefix that needs to be indexed. Minimum is `0`. Default is `2`.
+- `max_chars`: Maximum length of the prefix that needs to be indexed. Maximum is `20`. Default is `5`.
+
+## Enabling index prefixes on a field
+
+The following request creates an index named `products` with the `name` field configured to build a prefix index with length between `2` and `10` characters:
+
+```json
+PUT /products
+{
+  "mappings": {
+    "properties": {
+      "name": {
+        "type": "text",
+        "index_prefixes": {
+          "min_chars": 2,
+          "max_chars": 10
+        }
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+Index a document using the following command:
+
+```json
+PUT /products/_doc/1
+{
+  "name": "Ultra HD Television"
+}
+```
+{% include copy-curl.html %}
+
+The following search request demonstrates a prefix query that looks for documents where the `name` field starts with `ul`:
+
+```json
+POST /products/_search
+{
+  "query": {
+    "prefix": {
+      "name": "ul"
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+Expected result:
+
+```json
+{
+  ...
+  "hits": {
+    "total": {
+      "value": 1,
+      "relation": "eq"
+    },
+    "max_score": 1,
+    "hits": [
+      {
+        "_index": "products",
+        "_id": "1",
+        "_score": 1,
+        "_source": {
+          "name": "Ultra HD Television"
+        }
+      }
+    ]
+  }
+}
+```
+
+## Using default parameters with index prefixes
+
+The following command creates an index named `products_default` using `index_prefixes` with default parameters:
+
+```json
+PUT /products_default
+{
+  "mappings": {
+    "properties": {
+      "name": {
+        "type": "text",
+        "index_prefixes": {}
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}