Reduce allocations due to Jackson serialization. (#12468)

* Reduce allocations due to Jackson serialization.

This patch attacks two sources of allocations during Jackson
serialization:

1) ObjectMapper.writeValue and JsonGenerator.writeObject create a new
   DefaultSerializerProvider instance for each call. It has lots of
   fields and creates pressure on the garbage collector. So, this patch
   adds helper functions in JacksonUtils that enable reuse of
   SerializerProvider objects and updates various call sites to make
   use of this.

2) GroupByQueryToolChest copies the ObjectMapper for every query to
   install a special module that supports backwards compatibility with
   map-based rows. This isn't needed if resultAsArray is set and
   all servers are running Druid 0.16.0 or later. This release was a
   while ago. So, this patch disables backwards compatibility by default,
   which eliminates the need to copy the heavyweight ObjectMapper. The
   patch also introduces a configuration option that allows admins to
   explicitly enable backwards compatibility.

* Add test.

* Update additional call sites and add to forbidden APIs.

codestyle/druid-forbidden-apis.txt

@@ -1,6 +1,8 @@
 com.fasterxml.jackson.databind.ObjectMapper#reader(com.fasterxml.jackson.core.type.TypeReference) @ Use ObjectMapper#readerFor instead
 com.fasterxml.jackson.databind.ObjectMapper#reader(com.fasterxml.jackson.databind.JavaType) @ Use ObjectMapper#readerFor instead
 com.fasterxml.jackson.databind.ObjectMapper#reader(java.lang.Class) @ Use ObjectMapper#readerFor instead
+com.fasterxml.jackson.databind.ObjectMapper#writeValue(com.fasterxml.jackson.core.JsonGenerator, java.lang.Object) @ Use JacksonUtils#writeObjectUsingSerializerProvider to allow SerializerProvider reuse
+com.fasterxml.jackson.core.JsonGenerator#writeObject(java.lang.Object) @ Use JacksonUtils#writeObjectUsingSerializerProvider to allow SerializerProvider reuse
 com.google.common.base.Charsets @ Use java.nio.charset.StandardCharsets instead
 com.google.common.collect.Iterators#emptyIterator() @ Use java.util.Collections#emptyIterator()
 com.google.common.collect.Lists#newArrayList() @ Create java.util.ArrayList directly

core/src/main/java/org/apache/druid/java/util/common/jackson/JacksonUtils.java

@@ -19,9 +19,14 @@
 
 package org.apache.druid.java.util.common.jackson;
 
+import com.fasterxml.jackson.core.JsonGenerator;
 import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.JsonMappingException;
+import com.fasterxml.jackson.databind.JsonSerializer;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializerProvider;
 
+import javax.annotation.Nullable;
 import java.io.IOException;
 import java.util.Map;
 
@@ -40,7 +45,9 @@
       {
       };
 
-  /** Silences Jackson's {@link IOException}. */
+  /**
+   * Silences Jackson's {@link IOException}.
+   */
   public static <T> T readValue(ObjectMapper mapper, byte[] bytes, Class<T> valueClass)
   {
     try {
@@ -51,6 +58,37 @@ public static <T> T readValue(ObjectMapper mapper, byte[] bytes, Class<T> valueC
     }
   }
 
+  /**
+   * Returns a serializer for a particular class. If you have a {@link SerializerProvider}, this is better than calling
+   * {@link JsonGenerator#writeObject(Object)} or {@link ObjectMapper#writeValue(JsonGenerator, Object)}, because it
+   * avoids re-creating the {@link SerializerProvider} for each serialized object.
+   */
+  public static JsonSerializer<Object> getSerializer(final SerializerProvider serializerProvider, final Class<?> clazz)
+      throws JsonMappingException
+  {
+    // cache = true, property = null because this is what DefaultSerializerProvider.serializeValue would do.
+    return serializerProvider.findTypedValueSerializer(clazz, true, null);
+  }
+
+  /**
+   * Serializes an object using a {@link JsonGenerator}. If you have a {@link SerializerProvider}, this is better than
+   * calling {@link JsonGenerator#writeObject(Object)}, because it avoids re-creating the {@link SerializerProvider}
+   * for each serialized object.
+   */
+  public static void writeObjectUsingSerializerProvider(
+      final JsonGenerator jsonGenerator,
+      final SerializerProvider serializers,
+      @Nullable final Object o
+  ) throws IOException
+  {
+    if (o == null) {
+      jsonGenerator.writeNull();
+    } else {
+      final JsonSerializer<Object> serializer = getSerializer(serializers, o.getClass());
+      serializer.serialize(o, jsonGenerator, serializers);
+    }
+  }
+
   private JacksonUtils()
   {
   }

core/src/test/java/org/apache/druid/common/jackson/JacksonUtilsTest.java

@@ -0,0 +1,137 @@
+/*
+ * 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.druid.common.jackson;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import org.apache.druid.java.util.common.jackson.JacksonUtils;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+
+public class JacksonUtilsTest
+{
+  @Test
+  public void testWriteObjectUsingSerializerProvider() throws IOException
+  {
+    final ByteArrayOutputStream baos = new ByteArrayOutputStream();
+
+    final ObjectMapper objectMapper = new ObjectMapper();
+    final SerializerProvider serializers = objectMapper.getSerializerProviderInstance();
+
+    final JsonGenerator jg = objectMapper.getFactory().createGenerator(baos);
+    jg.writeStartArray();
+    JacksonUtils.writeObjectUsingSerializerProvider(jg, serializers, new SerializableClass(2));
+    JacksonUtils.writeObjectUsingSerializerProvider(jg, serializers, null);
+    JacksonUtils.writeObjectUsingSerializerProvider(jg, serializers, new SerializableClass(3));
+    jg.writeEndArray();
+    jg.close();
+
+    final List<SerializableClass> deserializedValues = objectMapper.readValue(
+        baos.toByteArray(),
+        new TypeReference<List<SerializableClass>>() {}
+    );
+
+    Assert.assertEquals(
+        Arrays.asList(new SerializableClass(2), null, new SerializableClass(3)),
+        deserializedValues
+    );
+  }
+
+  @Test
+  public void testWritePrimitivesUsingSerializerProvider() throws IOException
+  {
+    final ByteArrayOutputStream baos = new ByteArrayOutputStream();
+
+    final ObjectMapper objectMapper = new ObjectMapper();
+    final SerializerProvider serializers = objectMapper.getSerializerProviderInstance();
+
+    final JsonGenerator jg = objectMapper.getFactory().createGenerator(baos);
+    jg.writeStartArray();
+    JacksonUtils.writeObjectUsingSerializerProvider(jg, serializers, "foo");
+    JacksonUtils.writeObjectUsingSerializerProvider(jg, serializers, null);
+    JacksonUtils.writeObjectUsingSerializerProvider(jg, serializers, 1.23);
+    jg.writeEndArray();
+    jg.close();
+
+    final List<Object> deserializedValues = objectMapper.readValue(
+        baos.toByteArray(),
+        new TypeReference<List<Object>>() {}
+    );
+
+    Assert.assertEquals(
+        Arrays.asList("foo", null, 1.23),
+        deserializedValues
+    );
+  }
+
+  public static class SerializableClass
+  {
+    private final int value;
+
+    @JsonCreator
+    public SerializableClass(@JsonProperty("value") final int value)
+    {
+      this.value = value;
+    }
+
+    @JsonProperty
+    public int getValue()
+    {
+      return value;
+    }
+
+    @Override
+    public boolean equals(Object o)
+    {
+      if (this == o) {
+        return true;
+      }
+      if (o == null || getClass() != o.getClass()) {
+        return false;
+      }
+      SerializableClass that = (SerializableClass) o;
+      return value == that.value;
+    }
+
+    @Override
+    public int hashCode()
+    {
+      return Objects.hash(value);
+    }
+
+    @Override
+    public String toString()
+    {
+      return "SerializableClass{" +
+             "value=" + value +
+             '}';
+    }
+  }
+}

core/src/test/java/org/apache/druid/data/input/impl/prefetch/JsonIteratorTest.java

@@ -23,9 +23,11 @@
 import com.fasterxml.jackson.core.JsonGenerator;
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializerProvider;
 import com.fasterxml.jackson.dataformat.smile.SmileFactory;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
+import org.apache.druid.java.util.common.jackson.JacksonUtils;
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -50,9 +52,10 @@ public void testSerde() throws IOException
     };
     try (FileOutputStream fos = new FileOutputStream(testFile)) {
       final JsonGenerator jg = mapper.getFactory().createGenerator(fos);
+      final SerializerProvider serializers = mapper.getSerializerProviderInstance();
       jg.writeStartArray();
       for (Map<String, Object> mapFromList : expectedList) {
-        jg.writeObject(mapFromList);
+        JacksonUtils.writeObjectUsingSerializerProvider(jg, serializers, mapFromList);
       }
       jg.writeEndArray();
       jg.close();

docs/querying/groupbyquery.md

@@ -409,6 +409,7 @@ Supported runtime properties:
 |--------|-----------|-------|
 |`druid.query.groupBy.defaultStrategy`|Default groupBy query strategy.|v2|
 |`druid.query.groupBy.singleThreaded`|Merge results using a single thread.|false|
+|`druid.query.groupBy.intermediateResultAsMapCompat`|Whether Brokers are able to understand map-based result rows. Setting this to `true` adds some overhead to all groupBy queries. It is required for compatibility with data servers running versions older than 0.16.0, which introduced [array-based result rows](#array-based-result-rows).|false|
 
 Supported query contexts:
 

processing/src/main/java/org/apache/druid/jackson/DruidDefaultSerializersModule.java

@@ -31,6 +31,7 @@
 import org.apache.druid.java.util.common.guava.Accumulator;
 import org.apache.druid.java.util.common.guava.Sequence;
 import org.apache.druid.java.util.common.guava.Yielder;
+import org.apache.druid.java.util.common.jackson.JacksonUtils;
 import org.apache.druid.query.context.ResponseContext;
 import org.apache.druid.query.context.ResponseContextDeserializer;
 import org.joda.time.DateTimeZone;
@@ -93,11 +94,26 @@ public void serialize(Sequence value, final JsonGenerator jgen, SerializerProvid
                 null,
                 new Accumulator<Object, Object>()
                 {
+                  // Save allocations in jgen.writeObject by caching serializer.
+                  JsonSerializer<Object> serializer = null;
+                  Class<?> serializerClass = null;
+
                   @Override
-                  public Object accumulate(Object o, Object o1)
+                  public Object accumulate(Object ignored, Object object)
                   {
                     try {
-                      jgen.writeObject(o1);
+                      if (object == null) {
+                        jgen.writeNull();
+                      } else {
+                        final Class<?> clazz = object.getClass();
+
+                        if (serializerClass != clazz) {
+                          serializer = JacksonUtils.getSerializer(provider, clazz);
+                          serializerClass = clazz;
+                        }
+
+                        serializer.serialize(object, jgen, provider);
+                      }
                     }
                     catch (IOException e) {
                       throw new RuntimeException(e);
@@ -119,11 +135,27 @@ public Object accumulate(Object o, Object o1)
           public void serialize(Yielder yielder, final JsonGenerator jgen, SerializerProvider provider)
               throws IOException
           {
+            // Save allocations in jgen.writeObject by caching serializer.
+            JsonSerializer<Object> serializer = null;
+            Class<?> serializerClass = null;
+
             try {
               jgen.writeStartArray();
               while (!yielder.isDone()) {
                 final Object o = yielder.get();
-                jgen.writeObject(o);
+                if (o == null) {
+                  jgen.writeNull();
+                } else {
+                  final Class<?> clazz = o.getClass();
+
+                  if (serializerClass != clazz) {
+                    serializer = JacksonUtils.getSerializer(provider, clazz);
+                    serializerClass = clazz;
+                  }
+
+                  serializer.serialize(o, jgen, provider);
+                }
+
                 yielder = yielder.next(null);
               }
               jgen.writeEndArray();

processing/src/main/java/org/apache/druid/query/groupby/GroupByQueryConfig.java

@@ -105,6 +105,9 @@
   @JsonProperty
   private boolean vectorize = true;
 
+  @JsonProperty
+  private boolean intermediateResultAsMapCompat = false;
+
   @JsonProperty
   private boolean enableMultiValueUnnesting = true;
 
@@ -203,6 +206,11 @@ public boolean isVectorize()
     return vectorize;
   }
 
+  public boolean isIntermediateResultAsMapCompat()
+  {
+    return intermediateResultAsMapCompat;
+  }
+
   public boolean isForcePushDownNestedQuery()
   {
     return forcePushDownNestedQuery;

processing/src/main/java/org/apache/druid/query/groupby/GroupByQueryQueryToolChest.java

@@ -31,6 +31,7 @@
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Function;
 import com.google.common.base.Functions;
+import com.google.common.base.Supplier;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Lists;
 import com.google.inject.Inject;
@@ -40,6 +41,7 @@
 import org.apache.druid.java.util.common.guava.MappedSequence;
 import org.apache.druid.java.util.common.guava.Sequence;
 import org.apache.druid.java.util.common.guava.Sequences;
+import org.apache.druid.java.util.common.jackson.JacksonUtils;
 import org.apache.druid.query.CacheStrategy;
 import org.apache.druid.query.DataSource;
 import org.apache.druid.query.Query;
@@ -91,21 +93,24 @@ public class GroupByQueryQueryToolChest extends QueryToolChest<ResultRow, GroupB
   public static final String GROUP_BY_MERGE_KEY = "groupByMerge";
 
   private final GroupByStrategySelector strategySelector;
+  private final GroupByQueryConfig queryConfig;
   private final GroupByQueryMetricsFactory queryMetricsFactory;
 
   @VisibleForTesting
   public GroupByQueryQueryToolChest(GroupByStrategySelector strategySelector)
   {
-    this(strategySelector, DefaultGroupByQueryMetricsFactory.instance());
+    this(strategySelector, GroupByQueryConfig::new, DefaultGroupByQueryMetricsFactory.instance());
   }
 
   @Inject
   public GroupByQueryQueryToolChest(
       GroupByStrategySelector strategySelector,
+      Supplier<GroupByQueryConfig> queryConfigSupplier,
       GroupByQueryMetricsFactory queryMetricsFactory
   )
   {
     this.strategySelector = strategySelector;
+    this.queryConfig = queryConfigSupplier.get();
     this.queryMetricsFactory = queryMetricsFactory;
   }
 
@@ -415,6 +420,12 @@ public ObjectMapper decorateObjectMapper(final ObjectMapper objectMapper, final
   {
     final boolean resultAsArray = query.getContextBoolean(GroupByQueryConfig.CTX_KEY_ARRAY_RESULT_ROWS, false);
 
+    if (resultAsArray && !queryConfig.isIntermediateResultAsMapCompat()) {
+      // We can assume ResultRow are serialized and deserialized as arrays. No need for special decoration,
+      // and we can save the overhead of making a copy of the ObjectMapper.
+      return objectMapper;
+    }
+
     // Serializer that writes array- or map-based rows as appropriate, based on the "resultAsArray" setting.
     final JsonSerializer<ResultRow> serializer = new JsonSerializer<ResultRow>()
     {
@@ -426,9 +437,9 @@ public void serialize(
       ) throws IOException
       {
         if (resultAsArray) {
-          jg.writeObject(resultRow.getArray());
+          JacksonUtils.writeObjectUsingSerializerProvider(jg, serializers, resultRow.getArray());
         } else {
-          jg.writeObject(resultRow.toMapBasedRow(query));
+          JacksonUtils.writeObjectUsingSerializerProvider(jg, serializers, resultRow.toMapBasedRow(query));
         }
       }
     };