Add index mapping parameter for counted_keyword

With this commit we add a new mapping parameter `index` to the
`counted_keyword` mapping type. This allows to reduce disk usage for use
cases where indexed fields are not required.

Relates elastic#101826

x-pack/plugin/mapper-counted-keyword/src/main/java/org/elasticsearch/xpack/countedkeyword/CountedKeywordFieldMapper.java

@@ -78,16 +78,24 @@ public class CountedKeywordFieldMapper extends FieldMapper {
     public static final String CONTENT_TYPE = "counted_keyword";
     public static final String COUNT_FIELD_NAME_SUFFIX = "_count";
 
-    public static final FieldType FIELD_TYPE;
+    private static final FieldType FIELD_TYPE_INDEXED;
+    private static final FieldType FIELD_TYPE_NOT_INDEXED;
 
     static {
-        FieldType ft = new FieldType();
-        ft.setDocValuesType(DocValuesType.SORTED_SET);
-        ft.setTokenized(false);
-        ft.setOmitNorms(true);
-        ft.setIndexOptions(IndexOptions.DOCS);
-        ft.freeze();
-        FIELD_TYPE = freezeAndDeduplicateFieldType(ft);
+        FieldType indexed = new FieldType();
+        indexed.setDocValuesType(DocValuesType.SORTED_SET);
+        indexed.setTokenized(false);
+        indexed.setOmitNorms(true);
+        indexed.setIndexOptions(IndexOptions.DOCS);
+        FIELD_TYPE_INDEXED = freezeAndDeduplicateFieldType(indexed);
+
+        FieldType notIndexed = new FieldType();
+        notIndexed.setDocValuesType(DocValuesType.SORTED_SET);
+        notIndexed.setTokenized(false);
+        notIndexed.setOmitNorms(true);
+        notIndexed.setIndexOptions(IndexOptions.NONE);
+        FIELD_TYPE_NOT_INDEXED = freezeAndDeduplicateFieldType(notIndexed);
+
     }
 
     private static class CountedKeywordFieldType extends StringFieldType {
@@ -261,7 +269,12 @@ public TermsEnum termsEnum() throws IOException {
         }
     }
 
+    private static CountedKeywordFieldMapper toType(FieldMapper in) {
+        return (CountedKeywordFieldMapper) in;
+    }
+
     public static class Builder extends FieldMapper.Builder {
+        private final Parameter<Boolean> indexed = Parameter.indexParam(m -> toType(m).mappedFieldType.isIndexed(), true);
         private final Parameter<Map<String, String>> meta = Parameter.metaParam();
 
         protected Builder(String name) {
@@ -270,22 +283,24 @@ protected Builder(String name) {
 
         @Override
         protected Parameter<?>[] getParameters() {
-            return new Parameter<?>[] { meta };
+            return new Parameter<?>[] { meta, indexed };
         }
 
         @Override
         public FieldMapper build(MapperBuilderContext context) {
 
             BinaryFieldMapper countFieldMapper = new BinaryFieldMapper.Builder(name + COUNT_FIELD_NAME_SUFFIX, true).build(context);
+            boolean isIndexed = indexed.getValue();
+            FieldType ft = isIndexed ? FIELD_TYPE_INDEXED : FIELD_TYPE_NOT_INDEXED;
             return new CountedKeywordFieldMapper(
                 name,
-                FIELD_TYPE,
+                ft,
                 new CountedKeywordFieldType(
                     context.buildFullName(name),
-                    true,
+                    isIndexed,
                     false,
                     true,
-                    new TextSearchInfo(FIELD_TYPE, null, KEYWORD_ANALYZER, KEYWORD_ANALYZER),
+                    new TextSearchInfo(ft, null, KEYWORD_ANALYZER, KEYWORD_ANALYZER),
                     meta.getValue(),
                     countFieldMapper.fieldType()
                 ),

x-pack/plugin/src/yamlRestTest/resources/rest-api-spec/test/counted_keyword/10_basic.yml

@@ -14,6 +14,17 @@ setup:
                 type: counted_keyword
 
 
+  - do:
+      indices.create:
+        index: test-events-no-index
+        body:
+          mappings:
+            properties:
+              events:
+                type: counted_keyword
+                index: false
+
+
   - do:
       index:
         index: test-events
@@ -26,12 +37,18 @@ setup:
         id: "2"
         body: { "events": [ "a", "b", "b", "b", "c" ] }
 
+  - do:
+      index:
+        index: test-events-no-index
+        id: "1"
+        body: { "events": [ "a", "a", "b", "c" ] }
+
+
   - do:
       indices.refresh: { }
 
 ---
 "Counted Terms agg":
-
   - do:
       search:
         index: test-events
@@ -49,3 +66,22 @@ setup:
   - match: { aggregations.event_terms.buckets.2.key: "c" }
   - match: { aggregations.event_terms.buckets.2.doc_count: 2 }
   - length: { aggregations.event_terms.buckets: 3 }
+
+# although the field is not indexed, the counted_terms agg should still work
+  - do:
+      search:
+        index: test-events-no-index
+        body:
+          size: 0
+          aggs:
+            event_terms:
+              counted_terms:
+                field: events
+
+  - match: { aggregations.event_terms.buckets.0.key: "b" }
+  - match: { aggregations.event_terms.buckets.0.doc_count: 4 }
+  - match: { aggregations.event_terms.buckets.1.key: "a" }
+  - match: { aggregations.event_terms.buckets.1.doc_count: 3 }
+  - match: { aggregations.event_terms.buckets.2.key: "c" }
+  - match: { aggregations.event_terms.buckets.2.doc_count: 2 }
+  - length: { aggregations.event_terms.buckets: 3 }