KAFKA-14336: MetadataResponse#convertToNodeArray uses iteration (#12782)

Avoids stream allocation on hot code path in Admin#listOffsets

This patch avoids allocating the stream reference pipeline & spliterator for this case by explicitly allocating the pre-sized Node[] and using a for loop with int induction over the specified IDs List argument.

Reviewers: Apoorv Mittal <apoorvmittal10@gmail.com>, Kirk True <kirk@kirktrue.pro>, David Arthur <mumrah@gmail.com>

clients/src/main/java/org/apache/kafka/common/requests/MetadataResponse.java

@@ -177,12 +177,17 @@ public class MetadataResponse extends AbstractResponse {
     }
 
     private static Node[] convertToNodeArray(List<Integer> replicaIds, Map<Integer, Node> nodesById) {
-        return replicaIds.stream().map(replicaId -> {
+        // Since this is on hot path for partition info, use indexed iteration to avoid allocation overhead of Streams.
+        int size = replicaIds.size();
+        Node[] nodes = new Node[size];
+        for (int i = 0; i < size; i++) {
+            Integer replicaId = replicaIds.get(i);
             Node node = nodesById.get(replicaId);
             if (node == null)
-                return new Node(replicaId, "", -1);
-            return node;
-        }).toArray(Node[]::new);
+                node = new Node(replicaId, "", -1);
+            nodes[i] = node;
+        }
+        return nodes;
     }
 
     /**

jmh-benchmarks/src/main/java/org/apache/kafka/jmh/common/MetadataResponseBenchmark.java

@@ -0,0 +1,88 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.kafka.jmh.common;
+
+import org.apache.kafka.common.Node;
+import org.apache.kafka.common.PartitionInfo;
+import org.apache.kafka.common.TopicPartition;
+import org.apache.kafka.common.protocol.Errors;
+import org.apache.kafka.common.requests.MetadataResponse;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.RunnerException;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+import java.util.concurrent.TimeUnit;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+@State(Scope.Benchmark)
+@Fork(value = 1)
+@Warmup(iterations = 3, time = 5)
+@Measurement(iterations = 5, time = 5)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+public class MetadataResponseBenchmark {
+
+    @Param({"10", "500", "1000"})
+    private int nodes;
+
+    private MetadataResponse.PartitionMetadata metadata;
+    private Map<Integer, Node> nodesById;
+
+    @Setup
+    public void setup() {
+        metadata = new MetadataResponse.PartitionMetadata(Errors.UNKNOWN_SERVER_ERROR,
+                new TopicPartition("benchmark", 42),
+                Optional.of(4),
+                Optional.of(42),
+                IntStream.range(0, nodes).boxed().collect(Collectors.toList()),
+                IntStream.range(0, nodes).filter(i1 -> i1 % 3 != 0).boxed().collect(Collectors.toList()),
+                IntStream.range(0, nodes).filter(i2 -> i2 % 3 == 0).boxed().collect(Collectors.toList()));
+        nodesById = new HashMap<>(nodes);
+        for (int i = 0; i < nodes; i++) {
+            nodesById.put(i, new Node(i, "localhost", 1234));
+        }
+        nodesById = Collections.unmodifiableMap(nodesById);
+    }
+
+    @Benchmark
+    public PartitionInfo toPartitionInfo() {
+        return MetadataResponse.toPartitionInfo(metadata, nodesById);
+    }
+
+    public static void main(String[] args) throws RunnerException {
+        new Runner(new OptionsBuilder().include(MetadataResponseBenchmark.class.getSimpleName()).build()).run();
+    }
+
+}