Remove ChunkedToXContentBuilder (elastic#119310)

Reverts the introduction of the ChunkedToXContentBuilder to fix the various performance regressions it introduced and the theoretical impossibility of fixing its performance to rival that of the iterator based solution.
With the exception of a few minor adjustments that came out of changes already made on top of the builder migration this simply returns to the previous implementations (and some of the stuff in that code could be done better with the utilities available now).
I also verified that this solves the performance issues that we've been running into with the builder.

closes elastic#118647

This reverts commit 918a9cc
This reverts commit 8c37875
This reverts commit 11c2eb2
This reverts commit c311515

docs/changelog/119310.yaml

@@ -0,0 +1,6 @@
+pr: 119310
+summary: Remove ChunkedToXContentBuilder
+area: "Network"
+type: bug
+issues:
+ - 118647

modules/ingest-geoip/src/main/java/org/elasticsearch/ingest/geoip/IngestGeoIpMetadata.java

@@ -15,9 +15,10 @@
 import org.elasticsearch.cluster.DiffableUtils;
 import org.elasticsearch.cluster.NamedDiff;
 import org.elasticsearch.cluster.metadata.Metadata;
+import org.elasticsearch.common.collect.Iterators;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
-import org.elasticsearch.common.xcontent.ChunkedToXContent;
+import org.elasticsearch.common.xcontent.ChunkedToXContentHelper;
 import org.elasticsearch.ingest.geoip.direct.DatabaseConfigurationMetadata;
 import org.elasticsearch.xcontent.ConstructingObjectParser;
 import org.elasticsearch.xcontent.ParseField;
@@ -90,8 +91,8 @@ public static IngestGeoIpMetadata fromXContent(XContentParser parser) throws IOE
     }
 
     @Override
-    public Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params params) {
-        return ChunkedToXContent.builder(params).xContentObjectFields(DATABASES_FIELD.getPreferredName(), databases);
+    public Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params ignored) {
+        return Iterators.concat(ChunkedToXContentHelper.xContentValuesMap(DATABASES_FIELD.getPreferredName(), databases));
     }
 
     @Override

server/src/main/java/org/elasticsearch/action/admin/cluster/node/stats/NodeStats.java

@@ -15,9 +15,11 @@
 import org.elasticsearch.cluster.node.DiscoveryNodeRole;
 import org.elasticsearch.cluster.routing.allocation.DiskThresholdSettings;
 import org.elasticsearch.cluster.routing.allocation.NodeAllocationStats;
+import org.elasticsearch.common.collect.Iterators;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.ChunkedToXContent;
+import org.elasticsearch.common.xcontent.ChunkedToXContentHelper;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.discovery.DiscoveryStats;
 import org.elasticsearch.http.HttpStats;
@@ -38,10 +40,13 @@
 import org.elasticsearch.xcontent.ToXContent;
 
 import java.io.IOException;
+import java.util.Collections;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Objects;
 
+import static org.elasticsearch.common.xcontent.ChunkedToXContentHelper.singleChunk;
+
 /**
  * Node statistics (dynamic, changes depending on when created).
  */
@@ -342,7 +347,7 @@ public void writeTo(StreamOutput out) throws IOException {
 
     @Override
     public Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params outerParams) {
-        return ChunkedToXContent.builder(outerParams).append((builder, params) -> {
+        return Iterators.concat(singleChunk((builder, params) -> {
             builder.field("name", getNode().getName());
             builder.field("transport_address", getNode().getAddress().toString());
             builder.field("host", getNode().getHostName());
@@ -353,38 +358,47 @@ public Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params outerP
                 builder.value(role.roleName());
             }
             builder.endArray();
-
             if (getNode().getAttributes().isEmpty() == false) {
                 builder.startObject("attributes");
                 for (Map.Entry<String, String> attrEntry : getNode().getAttributes().entrySet()) {
                     builder.field(attrEntry.getKey(), attrEntry.getValue());
                 }
                 builder.endObject();
             }
+
             return builder;
-        })
-
-            .appendIfPresent(getIndices())
-            .append((builder, p) -> builder.value(ifPresent(getOs()), p).value(ifPresent(getProcess()), p).value(ifPresent(getJvm()), p))
-
-            .appendIfPresent(getThreadPool())
-            .appendIfPresent(getFs())
-            .appendIfPresent(getTransport())
-            .appendIfPresent(getHttp())
-            .appendIfPresent(getBreaker())
-            .appendIfPresent(getScriptStats())
-            .appendIfPresent(getDiscoveryStats())
-            .appendIfPresent(getIngestStats())
-            .appendIfPresent(getAdaptiveSelectionStats())
-            .appendIfPresent(getScriptCacheStats())
-            .append(
+        }),
+            ifPresent(getIndices()).toXContentChunked(outerParams),
+            singleChunk(
+                (builder, p) -> builder.value(ifPresent(getOs()), p).value(ifPresent(getProcess()), p).value(ifPresent(getJvm()), p)
+            ),
+            ifPresent(getThreadPool()).toXContentChunked(outerParams),
+            singleChunkIfPresent(getFs()),
+            ifPresent(getTransport()).toXContentChunked(outerParams),
+            ifPresent(getHttp()).toXContentChunked(outerParams),
+            singleChunkIfPresent(getBreaker()),
+            ifPresent(getScriptStats()).toXContentChunked(outerParams),
+            singleChunkIfPresent(getDiscoveryStats()),
+            ifPresent(getIngestStats()).toXContentChunked(outerParams),
+            singleChunkIfPresent(getAdaptiveSelectionStats()),
+            singleChunkIfPresent(getScriptCacheStats()),
+            singleChunk(
                 (builder, p) -> builder.value(ifPresent(getIndexingPressureStats()), p)
                     .value(ifPresent(getRepositoriesStats()), p)
                     .value(ifPresent(getNodeAllocationStats()), p)
-            );
+            )
+        );
+    }
+
+    private static ChunkedToXContent ifPresent(@Nullable ChunkedToXContent chunkedToXContent) {
+        return Objects.requireNonNullElse(chunkedToXContent, ChunkedToXContent.EMPTY);
     }
 
     private static ToXContent ifPresent(@Nullable ToXContent toXContent) {
         return Objects.requireNonNullElse(toXContent, ToXContent.EMPTY);
     }
+
+    private static Iterator<ToXContent> singleChunkIfPresent(ToXContent toXContent) {
+        return toXContent == null ? Collections.emptyIterator() : ChunkedToXContentHelper.singleChunk(toXContent);
+    }
 }

server/src/main/java/org/elasticsearch/action/admin/cluster/node/stats/NodesStatsResponse.java

@@ -14,9 +14,10 @@
 import org.elasticsearch.action.support.nodes.BaseNodesXContentResponse;
 import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.common.Strings;
+import org.elasticsearch.common.collect.Iterators;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
-import org.elasticsearch.common.xcontent.ChunkedToXContent;
+import org.elasticsearch.common.xcontent.ChunkedToXContentHelper;
 import org.elasticsearch.xcontent.ToXContent;
 
 import java.io.IOException;
@@ -41,12 +42,15 @@ protected void writeNodesTo(StreamOutput out, List<NodeStats> nodes) throws IOEx
 
     @Override
     protected Iterator<? extends ToXContent> xContentChunks(ToXContent.Params outerParams) {
-        return ChunkedToXContent.builder(outerParams)
-            .object(
-                "nodes",
-                getNodes().iterator(),
-                (b, ns) -> b.object(ns.getNode().getId(), ob -> ob.field("timestamp", ns.getTimestamp()).append(ns))
-            );
+        return Iterators.concat(
+            ChunkedToXContentHelper.startObject("nodes"),
+            Iterators.flatMap(getNodes().iterator(), nodeStats -> Iterators.concat(Iterators.single((builder, params) -> {
+                builder.startObject(nodeStats.getNode().getId());
+                builder.field("timestamp", nodeStats.getTimestamp());
+                return builder;
+            }), nodeStats.toXContentChunked(outerParams), ChunkedToXContentHelper.endObject())),
+            ChunkedToXContentHelper.endObject()
+        );
     }
 
     @Override

server/src/main/java/org/elasticsearch/action/admin/cluster/reroute/ClusterRerouteResponse.java

@@ -13,18 +13,20 @@
 import org.elasticsearch.action.support.master.IsAcknowledgedSupplier;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.routing.allocation.RoutingExplanations;
+import org.elasticsearch.common.collect.Iterators;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.logging.DeprecationCategory;
 import org.elasticsearch.common.logging.DeprecationLogger;
-import org.elasticsearch.common.xcontent.ChunkedToXContent;
+import org.elasticsearch.common.xcontent.ChunkedToXContentHelper;
 import org.elasticsearch.common.xcontent.ChunkedToXContentObject;
 import org.elasticsearch.core.RestApiVersion;
 import org.elasticsearch.core.UpdateForV10;
 import org.elasticsearch.rest.action.search.RestSearchAction;
 import org.elasticsearch.xcontent.ToXContent;
 
 import java.io.IOException;
+import java.util.Collections;
 import java.util.Iterator;
 import java.util.Objects;
 
@@ -92,14 +94,17 @@ public Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params outerP
         if (emitState(outerParams)) {
             deprecationLogger.critical(DeprecationCategory.API, "reroute_cluster_state", STATE_FIELD_DEPRECATION_MESSAGE);
         }
-        return ChunkedToXContent.builder(outerParams).object(b -> {
-            b.field(ACKNOWLEDGED_KEY, isAcknowledged());
-            if (emitState(outerParams)) {
-                b.xContentObject("state", state);
-            }
-            if (outerParams.paramAsBoolean("explain", false)) {
-                b.append(explanations);
-            }
-        });
+        return Iterators.concat(
+            Iterators.single((builder, params) -> builder.startObject().field(ACKNOWLEDGED_KEY, isAcknowledged())),
+            emitState(outerParams)
+                ? ChunkedToXContentHelper.wrapWithObject("state", state.toXContentChunked(outerParams))
+                : Collections.emptyIterator(),
+            Iterators.single((builder, params) -> {
+                if (params.paramAsBoolean("explain", false)) {
+                    explanations.toXContent(builder, params);
+                }
+                return builder.endObject();
+            })
+        );
     }
 }

server/src/main/java/org/elasticsearch/action/bulk/BulkResponse.java

@@ -14,7 +14,6 @@
 import org.elasticsearch.common.collect.Iterators;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
-import org.elasticsearch.common.xcontent.ChunkedToXContent;
 import org.elasticsearch.common.xcontent.ChunkedToXContentObject;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.xcontent.ToXContent;
@@ -158,13 +157,14 @@ public void writeTo(StreamOutput out) throws IOException {
 
     @Override
     public Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params params) {
-        return ChunkedToXContent.builder(params).object(ob -> ob.append((b, p) -> {
-            b.field(ERRORS, hasFailures());
-            b.field(TOOK, tookInMillis);
+        return Iterators.concat(Iterators.single((builder, p) -> {
+            builder.startObject();
+            builder.field(ERRORS, hasFailures());
+            builder.field(TOOK, tookInMillis);
             if (ingestTookInMillis != BulkResponse.NO_INGEST_TOOK) {
-                b.field(INGEST_TOOK, ingestTookInMillis);
+                builder.field(INGEST_TOOK, ingestTookInMillis);
             }
-            return b;
-        }).array(ITEMS, Iterators.forArray(responses)));
+            return builder.startArray(ITEMS);
+        }), Iterators.forArray(responses), Iterators.<ToXContent>single((builder, p) -> builder.endArray().endObject()));
     }
 }

server/src/main/java/org/elasticsearch/action/search/SearchResponse.java

@@ -14,12 +14,13 @@
 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.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;
@@ -382,17 +383,24 @@ public Clusters getClusters() {
     @Override
     public Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params params) {
         assert hasReferences();
-        return ChunkedToXContent.builder(params).xContentObject(innerToXContentChunked(params));
+        return Iterators.concat(
+            ChunkedToXContentHelper.startObject(),
+            this.innerToXContentChunked(params),
+            ChunkedToXContentHelper.endObject()
+        );
     }
 
     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 Iterators.concat(
+            ChunkedToXContentHelper.singleChunk(SearchResponse.this::headerToXContent),
+            Iterators.single(clusters),
+            Iterators.concat(
+                hits.toXContentChunked(params),
+                aggregations == null ? Collections.emptyIterator() : ChunkedToXContentHelper.singleChunk(aggregations),
+                suggest == null ? Collections.emptyIterator() : ChunkedToXContentHelper.singleChunk(suggest),
+                profileResults == null ? Collections.emptyIterator() : ChunkedToXContentHelper.singleChunk(profileResults)
+            )
+        );
     }
 
     public XContentBuilder headerToXContent(XContentBuilder builder, ToXContent.Params params) throws IOException {

server/src/main/java/org/elasticsearch/action/support/broadcast/ChunkedBroadcastResponse.java

@@ -9,8 +9,9 @@
 package org.elasticsearch.action.support.broadcast;
 
 import org.elasticsearch.action.support.DefaultShardOperationFailedException;
+import org.elasticsearch.common.collect.Iterators;
 import org.elasticsearch.common.io.stream.StreamInput;
-import org.elasticsearch.common.xcontent.ChunkedToXContent;
+import org.elasticsearch.common.xcontent.ChunkedToXContentHelper;
 import org.elasticsearch.common.xcontent.ChunkedToXContentObject;
 import org.elasticsearch.rest.action.RestActions;
 import org.elasticsearch.xcontent.ToXContent;
@@ -35,8 +36,11 @@ public ChunkedBroadcastResponse(
 
     @Override
     public final Iterator<ToXContent> toXContentChunked(ToXContent.Params params) {
-        return ChunkedToXContent.builder(params)
-            .object(ob -> ob.append((b, p) -> RestActions.buildBroadcastShardsHeader(b, p, this)).append(this::customXContentChunks));
+        return Iterators.concat(Iterators.single((b, p) -> {
+            b.startObject();
+            RestActions.buildBroadcastShardsHeader(b, p, this);
+            return b;
+        }), customXContentChunks(params), ChunkedToXContentHelper.endObject());
     }
 
     protected abstract Iterator<ToXContent> customXContentChunks(ToXContent.Params params);

server/src/main/java/org/elasticsearch/action/support/nodes/BaseNodesXContentResponse.java

@@ -11,7 +11,8 @@
 
 import org.elasticsearch.action.FailedNodeException;
 import org.elasticsearch.cluster.ClusterName;
-import org.elasticsearch.common.xcontent.ChunkedToXContent;
+import org.elasticsearch.common.collect.Iterators;
+import org.elasticsearch.common.xcontent.ChunkedToXContentHelper;
 import org.elasticsearch.common.xcontent.ChunkedToXContentObject;
 import org.elasticsearch.rest.action.RestActions;
 import org.elasticsearch.xcontent.ToXContent;
@@ -29,12 +30,11 @@ protected BaseNodesXContentResponse(ClusterName clusterName, List<TNodeResponse>
 
     @Override
     public final Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params params) {
-        return ChunkedToXContent.builder(params)
-            .object(
-                ob -> ob.append((b, p) -> RestActions.buildNodesHeader(b, p, this))
-                    .field("cluster_name", getClusterName().value())
-                    .append(xContentChunks(params))
-            );
+        return Iterators.concat(Iterators.single((b, p) -> {
+            b.startObject();
+            RestActions.buildNodesHeader(b, p, this);
+            return b.field("cluster_name", getClusterName().value());
+        }), xContentChunks(params), ChunkedToXContentHelper.endObject());
     }
 
     protected abstract Iterator<? extends ToXContent> xContentChunks(ToXContent.Params outerParams);

server/src/main/java/org/elasticsearch/cluster/ClusterFeatures.java

@@ -11,9 +11,10 @@
 
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
+import org.elasticsearch.common.collect.Iterators;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
-import org.elasticsearch.common.xcontent.ChunkedToXContent;
+import org.elasticsearch.common.xcontent.ChunkedToXContentHelper;
 import org.elasticsearch.common.xcontent.ChunkedToXContentObject;
 import org.elasticsearch.features.NodeFeature;
 import org.elasticsearch.xcontent.ToXContent;
@@ -278,12 +279,15 @@ public ClusterFeatures apply(ClusterFeatures part) {
 
     @Override
     public Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params params) {
-        return ChunkedToXContent.builder(params)
-            .array(nodeFeatures.entrySet().stream().sorted(Map.Entry.comparingByKey()).iterator(), e -> (builder, p) -> {
+        return Iterators.concat(
+            ChunkedToXContentHelper.startArray(),
+            nodeFeatures.entrySet().stream().sorted(Map.Entry.comparingByKey()).<ToXContent>map(e -> (builder, p) -> {
                 String[] features = e.getValue().toArray(String[]::new);
                 Arrays.sort(features);
                 return builder.startObject().field("node_id", e.getKey()).array("features", features).endObject();
-            });
+            }).iterator(),
+            ChunkedToXContentHelper.endArray()
+        );
     }
 
     @Override