Uses norms for exists query if enabled (#27237)

* Uses norms for exists query if enabled

This change means that for indexes created from 6.1.0, if normas are enabled we will not write the field name to the `_field_names` field and for an exists query we will instead use the NormsFieldExistsQuery which was added in Lucene 7.1.0. If norms are not enabled or if the index was created before 6.1.0 `_field_names` will be used as before.

* Fixes tests

core/src/main/java/org/elasticsearch/index/mapper/TextFieldMapper.java

@@ -23,7 +23,7 @@ import org.apache.lucene.document.Field;
 import org.apache.lucene.index.IndexOptions;
 import org.apache.lucene.index.IndexableField;
 import org.apache.lucene.index.Term;
-import org.apache.lucene.search.DocValuesFieldExistsQuery;
+import org.apache.lucene.search.NormsFieldExistsQuery;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.TermQuery;
 import org.elasticsearch.common.settings.Settings;
@@ -280,10 +280,10 @@ public class TextFieldMapper extends FieldMapper {
 
         @Override
         public Query existsQuery(QueryShardContext context) {
-            if (hasDocValues()) {
+            if (omitNorms()) {
-                return new DocValuesFieldExistsQuery(name());
-            } else {
                 return new TermQuery(new Term(FieldNamesFieldMapper.NAME, name()));
+            } else {
+                return new NormsFieldExistsQuery(name());
             }
         }
 
@@ -345,7 +345,9 @@ public class TextFieldMapper extends FieldMapper {
         if (fieldType().indexOptions() != IndexOptions.NONE || fieldType().stored()) {
             Field field = new Field(fieldType().name(), value, fieldType());
             fields.add(field);
-            createFieldNamesField(context, fields);
+            if (fieldType().omitNorms()) {
+                createFieldNamesField(context, fields);
+            }
         }
     }
 

core/src/test/java/org/elasticsearch/index/mapper/FieldNamesFieldMapperTests.java

@@ -26,6 +26,7 @@ import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.test.ESSingleNodeTestCase;
 
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.Set;
 import java.util.SortedSet;
 import java.util.TreeSet;
@@ -87,7 +88,7 @@ public class FieldNamesFieldMapperTests extends ESSingleNodeTestCase {
                 .bytes(),
                 XContentType.JSON));
 
-        assertFieldNames(set("a"), doc);
+        assertFieldNames(Collections.emptySet(), doc);
     }
 
     public void testExplicitEnabled() throws Exception {

core/src/test/java/org/elasticsearch/index/query/ExistsQueryBuilderTests.java

@@ -24,6 +24,7 @@ import org.apache.lucene.search.BooleanQuery;
 import org.apache.lucene.search.ConstantScoreQuery;
 import org.apache.lucene.search.DocValuesFieldExistsQuery;
 import org.apache.lucene.search.MatchNoDocsQuery;
+import org.apache.lucene.search.NormsFieldExistsQuery;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.TermQuery;
 import org.elasticsearch.Version;
@@ -113,6 +114,10 @@ public class ExistsQueryBuilderTests extends AbstractQueryTestCase<ExistsQueryBu
                 assertThat(constantScoreQuery.getQuery(), instanceOf(DocValuesFieldExistsQuery.class));
                 DocValuesFieldExistsQuery dvExistsQuery = (DocValuesFieldExistsQuery) constantScoreQuery.getQuery();
                 assertEquals(field, dvExistsQuery.getField());
+            } else if (context.getQueryShardContext().getMapperService().fullName(field).omitNorms() == false) {
+                assertThat(constantScoreQuery.getQuery(), instanceOf(NormsFieldExistsQuery.class));
+                NormsFieldExistsQuery normsExistsQuery = (NormsFieldExistsQuery) constantScoreQuery.getQuery();
+                assertEquals(field, normsExistsQuery.getField());
             } else {
                 assertThat(constantScoreQuery.getQuery(), instanceOf(TermQuery.class));
                 TermQuery termQuery = (TermQuery) constantScoreQuery.getQuery();

core/src/test/java/org/elasticsearch/index/query/RangeQueryBuilderTests.java

@@ -26,6 +26,7 @@ import org.apache.lucene.search.ConstantScoreQuery;
 import org.apache.lucene.search.DocValuesFieldExistsQuery;
 import org.apache.lucene.search.IndexOrDocValuesQuery;
 import org.apache.lucene.search.MatchNoDocsQuery;
+import org.apache.lucene.search.NormsFieldExistsQuery;
 import org.apache.lucene.search.PointRangeQuery;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.TermQuery;
@@ -129,6 +130,9 @@ public class RangeQueryBuilderTests extends AbstractQueryTestCase<RangeQueryBuil
                 if (context.mapperService().getIndexSettings().getIndexVersionCreated().onOrAfter(Version.V_6_1_0)
                         && context.mapperService().fullName(queryBuilder.fieldName()).hasDocValues()) {
                     expectedQuery = new ConstantScoreQuery(new DocValuesFieldExistsQuery(queryBuilder.fieldName()));
+                } else if (context.mapperService().getIndexSettings().getIndexVersionCreated().onOrAfter(Version.V_6_1_0)
+                        && context.mapperService().fullName(queryBuilder.fieldName()).omitNorms() == false) {
+                    expectedQuery = new ConstantScoreQuery(new NormsFieldExistsQuery(queryBuilder.fieldName()));
                 } else {
                     expectedQuery = new ConstantScoreQuery(new TermQuery(new Term(FieldNamesFieldMapper.NAME, queryBuilder.fieldName())));
                 }