Ignore conflicting fields during dynamic mapping update

This fixes a bug when concurrently executing index requests that have different types for the same field.

server/src/internalClusterTest/java/org/elasticsearch/index/mapper/DynamicMappingIT.java

@@ -63,6 +63,8 @@
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.hasKey;
 import static org.hamcrest.Matchers.instanceOf;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.oneOf;
 
 public class DynamicMappingIT extends ESIntegTestCase {
 
@@ -190,6 +192,35 @@ private Map<String, Object> indexConcurrently(int numberOfFieldsToCreate, Settin
         return properties;
     }
 
+    public void testConcurrentDynamicMappingsWithConflictingType() throws Throwable {
+        int numberOfDocsToCreate = 16;
+        indicesAdmin().prepareCreate("index").setSettings(Settings.builder()).get();
+        ensureGreen("index");
+        final AtomicReference<Throwable> error = new AtomicReference<>();
+        startInParallel(numberOfDocsToCreate, i -> {
+            try {
+                assertEquals(
+                    DocWriteResponse.Result.CREATED,
+                    prepareIndex("index").setId(Integer.toString(i)).setSource("field" + i, 0, "field" + (i + 1), 0.1).get().getResult()
+                );
+            } catch (Exception e) {
+                error.compareAndSet(null, e);
+            }
+        });
+        if (error.get() != null) {
+            throw error.get();
+        }
+        client().admin().indices().prepareRefresh("index").get();
+        for (int i = 0; i < numberOfDocsToCreate; ++i) {
+            assertTrue(client().prepareGet("index", Integer.toString(i)).get().isExists());
+        }
+        Map<String, Object> index = indicesAdmin().prepareGetMappings("index").get().getMappings().get("index").getSourceAsMap();
+        for (int i = 0, j = 1; i < numberOfDocsToCreate; i++, j++) {
+            assertThat(new WriteField("properties.field" + i + ".type", () -> index).get(null), is(oneOf("long", "float")));
+            assertThat(new WriteField("properties.field" + j + ".type", () -> index).get(null), is(oneOf("long", "float")));
+        }
+    }
+
     public void testPreflightCheckAvoidsMaster() throws InterruptedException, IOException {
         // can't use INDEX_MAPPING_TOTAL_FIELDS_LIMIT_SETTING nor INDEX_MAPPING_DEPTH_LIMIT_SETTING as a check here, as that is already
         // checked at parse time, see testTotalFieldsLimitForDynamicMappingsUpdateCheckedAtDocumentParseTime

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

@@ -677,14 +677,30 @@ private static Map<String, Mapper> buildMergedMappers(
                     // replaces an existing one.
                     if (objectMergeContext.getMapperBuilderContext().getMergeReason() == MergeReason.INDEX_TEMPLATE) {
                         putMergedMapper(mergedMappers, mergeWithMapper);
-                    } else {
+                    } else if (isConflictingDynamicMapping(objectMergeContext, mergeWithMapper, mergeIntoMapper) == false) {
                         putMergedMapper(mergedMappers, mergeIntoMapper.merge(mergeWithMapper, objectMergeContext));
                     }
                 }
             }
             return Map.copyOf(mergedMappers);
         }
 
+        /*
+         * We're ignoring the field if a dynamic mapping update tries to define a conflicting field type (dynamic mappings update)
+         * This is caused by another index request with a different value racing to update the mappings.
+         * After ignoring the update the index request will be re-tried and sees the updated mappings for this field.
+         * The updated mappings will be taken into account when parsing the document
+         * (for example by coercing the value, ignore_malformed values, or failing the index request due to a type conflict).
+         */
+        private static boolean isConflictingDynamicMapping(
+            MapperMergeContext objectMergeContext,
+            Mapper mergeWithMapper,
+            Mapper mergeIntoMapper
+        ) {
+            return objectMergeContext.getMapperBuilderContext().getMergeReason().isAutoUpdate()
+                && mergeIntoMapper.typeName().equals(mergeWithMapper.typeName()) == false;
+        }
+
         private static void putMergedMapper(Map<String, Mapper> mergedMappers, @Nullable Mapper merged) {
             if (merged != null) {
                 mergedMappers.put(merged.leafName(), merged);