Fix inefficient org.elasticsearch.index.mapper.Mapper#getTotalFieldsCount implementations (elastic#119555) (elastic#119557)

This is eating up a lot of CPU when creating indices and visibly slowing
down many-shards benchmarks. Looking the profiling the cost of these
implementations is almost exclusively the cost of the stream abstraction
overhead (because we needlessly create the stream for every field mapper).
Keeping it simple and using iterators almost completely removes the cost
of this thing from profiling.

Author: original-brownbear

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

@@ -57,7 +57,6 @@
 import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Supplier;
-import java.util.stream.Stream;
 
 import static org.elasticsearch.core.Strings.format;
 
@@ -444,7 +443,11 @@ protected void doXContentBody(XContentBuilder builder, Params params) throws IOE
 
     @Override
     public int getTotalFieldsCount() {
-        return 1 + Stream.of(builderParams.multiFields.mappers).mapToInt(FieldMapper::getTotalFieldsCount).sum();
+        int sum = 1;
+        for (FieldMapper mapper : builderParams.multiFields.mappers) {
+            sum += mapper.getTotalFieldsCount();
+        }
+        return sum;
     }
 
     public Map<String, NamedAnalyzer> indexAnalyzers() {

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

@@ -263,7 +263,11 @@ public ObjectMapper build(MapperBuilderContext context) {
 
     @Override
     public int getTotalFieldsCount() {
-        return 1 + mappers.values().stream().mapToInt(Mapper::getTotalFieldsCount).sum();
+        int sum = 1;
+        for (Mapper mapper : mappers.values()) {
+            sum += mapper.getTotalFieldsCount();
+        }
+        return sum;
     }
 
     public static class TypeParser implements Mapper.TypeParser {

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

@@ -538,6 +538,6 @@ private static boolean processField(
 
     @Override
     public int getTotalFieldsCount() {
-        return mappers.values().stream().mapToInt(Mapper::getTotalFieldsCount).sum() + runtimeFields.size();
+        return super.getTotalFieldsCount() - 1 + runtimeFields.size();
     }
 }