From a4d232521b250e6df883d45dda8629859d38f858 Mon Sep 17 00:00:00 2001
From: Armin Braun <me@obrown.io>
Date: Sat, 4 Jan 2025 14:41:22 +0100
Subject: [PATCH] Fix inefficient
 org.elasticsearch.index.mapper.Mapper#getTotalFieldsCount implementations

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.
---
 .../java/org/elasticsearch/index/mapper/FieldMapper.java   | 7 +++++--
 .../java/org/elasticsearch/index/mapper/ObjectMapper.java  | 6 +++++-
 .../org/elasticsearch/index/mapper/RootObjectMapper.java   | 2 +-
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/server/src/main/java/org/elasticsearch/index/mapper/FieldMapper.java b/server/src/main/java/org/elasticsearch/index/mapper/FieldMapper.java
index ffd60efc772f9..5bbecbf117dba 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/FieldMapper.java
+++ b/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() {
diff --git a/server/src/main/java/org/elasticsearch/index/mapper/ObjectMapper.java b/server/src/main/java/org/elasticsearch/index/mapper/ObjectMapper.java
index 6a107dbaa9e63..f4084b3ede24f 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/ObjectMapper.java
+++ b/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 {
diff --git a/server/src/main/java/org/elasticsearch/index/mapper/RootObjectMapper.java b/server/src/main/java/org/elasticsearch/index/mapper/RootObjectMapper.java
index ce983e8a327c9..2fe82b4eacfc5 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/RootObjectMapper.java
+++ b/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();
     }
 }