From e90fb0c8f70a0e1b9d0ef969d9cf9aae02068255 Mon Sep 17 00:00:00 2001
From: Armin Braun <me@obrown.io>
Date: Mon, 24 Feb 2025 12:00:29 +0100
Subject: [PATCH] Speedup SearchResponse serialization (#123211)

No need to have a nested concat here. There's obviously lots and lots of
room for optimization on this one, but just flattening out one obvious
step here outright halves the number of method calls required when
serializing a search response. Given that method calls can consume up to
half the serialization cost this change might massively speed up some
usecases.
---
 .../action/search/SearchResponse.java         | 26 ++++++++++++-------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/server/src/main/java/org/elasticsearch/action/search/SearchResponse.java b/server/src/main/java/org/elasticsearch/action/search/SearchResponse.java
index d67d5d2faf47e..8a94f0fd15bd8 100644
--- a/server/src/main/java/org/elasticsearch/action/search/SearchResponse.java
+++ b/server/src/main/java/org/elasticsearch/action/search/SearchResponse.java
@@ -14,13 +14,14 @@
 import org.elasticsearch.action.OriginalIndices;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.bytes.BytesReference;
+import org.elasticsearch.common.collect.Iterators;
 import org.elasticsearch.common.io.stream.DelayableWriteable;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.common.lucene.Lucene;
 import org.elasticsearch.common.util.concurrent.ConcurrentCollections;
-import org.elasticsearch.common.xcontent.ChunkedToXContent;
+import org.elasticsearch.common.xcontent.ChunkedToXContentHelper;
 import org.elasticsearch.common.xcontent.ChunkedToXContentObject;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.core.RefCounted;
@@ -391,17 +392,24 @@ public Clusters getClusters() {
     @Override
     public Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params params) {
         assert hasReferences();
-        return ChunkedToXContent.builder(params).xContentObject(innerToXContentChunked(params));
+        return getToXContentIterator(true, params);
     }
 
     public Iterator<? extends ToXContent> innerToXContentChunked(ToXContent.Params params) {
-        return ChunkedToXContent.builder(params)
-            .append(SearchResponse.this::headerToXContent)
-            .append(clusters)
-            .append(hits)
-            .appendIfPresent(aggregations)
-            .appendIfPresent(suggest)
-            .appendIfPresent(profileResults);
+        return getToXContentIterator(false, params);
+    }
+
+    private Iterator<ToXContent> getToXContentIterator(boolean wrapInObject, ToXContent.Params params) {
+        return Iterators.concat(
+            wrapInObject ? ChunkedToXContentHelper.startObject() : Collections.emptyIterator(),
+            ChunkedToXContentHelper.singleChunk(SearchResponse.this::headerToXContent),
+            Iterators.single(clusters),
+            hits.toXContentChunked(params),
+            aggregations == null ? Collections.emptyIterator() : ChunkedToXContentHelper.singleChunk(aggregations),
+            suggest == null ? Collections.emptyIterator() : ChunkedToXContentHelper.singleChunk(suggest),
+            profileResults == null ? Collections.emptyIterator() : ChunkedToXContentHelper.singleChunk(profileResults),
+            wrapInObject ? ChunkedToXContentHelper.endObject() : Collections.emptyIterator()
+        );
     }
 
     public XContentBuilder headerToXContent(XContentBuilder builder, ToXContent.Params params) throws IOException {