Improve the error message when loading text fielddata. (#52753)

Emphasize keyword over fielddata as the preferred way to use String fields for aggregations or sorting.

client/rest-high-level/src/test/java/org/elasticsearch/client/GraphIT.java

@@ -37,33 +37,33 @@ import java.util.HashMap;
 import java.util.Map;
 
 public class GraphIT extends ESRestHighLevelClientTestCase {
-    
+
     @Before
     public void indexDocuments() throws IOException {
         // Create chain of doc IDs across indices 1->2->3
         Request doc1 = new Request(HttpPut.METHOD_NAME, "/index1/_doc/1");
         doc1.setJsonEntity("{ \"num\":[1], \"const\":\"start\"}");
         client().performRequest(doc1);
-        
+
         Request doc2 = new Request(HttpPut.METHOD_NAME, "/index2/_doc/1");
         doc2.setJsonEntity("{\"num\":[1,2], \"const\":\"foo\"}");
         client().performRequest(doc2);
-        
+
         Request doc3 = new Request(HttpPut.METHOD_NAME, "/index2/_doc/2");
         doc3.setJsonEntity("{\"num\":[2,3], \"const\":\"foo\"}");
-        client().performRequest(doc3);        
+        client().performRequest(doc3);
 
         Request doc4 = new Request(HttpPut.METHOD_NAME, "/index_no_field_data/_doc/2");
         doc4.setJsonEntity("{\"num\":\"string\", \"const\":\"foo\"}");
-        client().performRequest(doc4);        
-        
+        client().performRequest(doc4);
+
         Request doc5 = new Request(HttpPut.METHOD_NAME, "/index_no_field_data/_doc/2");
         doc5.setJsonEntity("{\"num\":[2,4], \"const\":\"foo\"}");
-        client().performRequest(doc5);        
+        client().performRequest(doc5);
+
 
-        
-        client().performRequest(new Request(HttpPost.METHOD_NAME, "/_refresh"));            
-    }    
+        client().performRequest(new Request(HttpPost.METHOD_NAME, "/_refresh"));
+    }
 
     public void testCleanExplore() throws Exception {
         GraphExploreRequest graphExploreRequest = new GraphExploreRequest();
@@ -75,7 +75,7 @@ public class GraphIT extends ESRestHighLevelClientTestCase {
             if (i == 0) {
                 guidingQuery = new TermQueryBuilder("const.keyword", "start");
             } else if (randomBoolean()){
-                guidingQuery = new TermQueryBuilder("const.keyword", "foo");                
+                guidingQuery = new TermQueryBuilder("const.keyword", "foo");
             }
             Hop hop = graphExploreRequest.createNextHop(guidingQuery);
             VertexRequest vr = hop.addVertexRequest("num");
@@ -94,13 +94,13 @@ public class GraphIT extends ESRestHighLevelClientTestCase {
         }
         assertEquals(expectedTermsAndDepths, actualTermsAndDepths);
         assertThat(exploreResponse.isTimedOut(), Matchers.is(false));
-        ShardOperationFailedException[] failures = exploreResponse.getShardFailures();        
+        ShardOperationFailedException[] failures = exploreResponse.getShardFailures();
         assertThat(failures.length, Matchers.equalTo(0));
-        
+
     }
 
     public void testBadExplore() throws Exception {
-        //Explore indices where lack of fielddata=true on one index leads to partial failures 
+        //Explore indices where lack of fielddata=true on one index leads to partial failures
         GraphExploreRequest graphExploreRequest = new GraphExploreRequest();
         graphExploreRequest.indices("index1", "index2", "index_no_field_data");
         graphExploreRequest.useSignificance(false);
@@ -110,7 +110,7 @@ public class GraphIT extends ESRestHighLevelClientTestCase {
             if (i == 0) {
                 guidingQuery = new TermQueryBuilder("const.keyword", "start");
             } else if (randomBoolean()){
-                guidingQuery = new TermQueryBuilder("const.keyword", "foo");                
+                guidingQuery = new TermQueryBuilder("const.keyword", "foo");
             }
             Hop hop = graphExploreRequest.createNextHop(guidingQuery);
             VertexRequest vr = hop.addVertexRequest("num");
@@ -131,9 +131,9 @@ public class GraphIT extends ESRestHighLevelClientTestCase {
         assertThat(exploreResponse.isTimedOut(), Matchers.is(false));
         ShardOperationFailedException[] failures = exploreResponse.getShardFailures();
         assertThat(failures.length, Matchers.equalTo(1));
-        assertTrue(failures[0].reason().contains("Fielddata is disabled"));
-        
+        assertTrue(failures[0].reason().contains("Text fields are not optimised for operations that require per-document field data"));
+
     }
-    
-    
+
+
 }

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

@@ -751,9 +751,10 @@ public class TextFieldMapper extends FieldMapper {
         @Override
         public IndexFieldData.Builder fielddataBuilder(String fullyQualifiedIndexName) {
             if (fielddata == false) {
-                throw new IllegalArgumentException("Fielddata is disabled on text fields by default. Set fielddata=true on [" + name()
-                        + "] in order to load fielddata in memory by uninverting the inverted index. Note that this can however "
-                                + "use significant memory. Alternatively use a keyword field instead.");
+            throw new IllegalArgumentException("Text fields are not optimised for operations that require per-document "
+                + "field data like aggregations and sorting, so these operations are disabled by default. Please use a "
+                    + "keyword field instead. Alternatively, set fielddata=true on [" + name() + "] in order to load "
+                        + "field data by uninverting the inverted index. Note that this can use significant memory.");
             }
             return new PagedBytesIndexFieldData.Builder(fielddataMinFrequency, fielddataMaxFrequency, fielddataMinSegmentSize);
         }

server/src/test/java/org/elasticsearch/index/mapper/TextFieldMapperTests.java

@@ -515,7 +515,7 @@ public class TextFieldMapperTests extends ESSingleNodeTestCase {
             FieldMapper fieldMapper = (FieldMapper) disabledMapper.mappers().getMapper("field");
             fieldMapper.fieldType().fielddataBuilder("test");
         });
-        assertThat(e.getMessage(), containsString("Fielddata is disabled"));
+        assertThat(e.getMessage(), containsString("Text fields are not optimised for operations that require per-document field data"));
 
         mapping = Strings.toString(XContentFactory.jsonBuilder().startObject().startObject("type")
                 .startObject("properties").startObject("field")