Allow query through router when load moving average extension (#11276)

* init commit

* change NoopQuerySegmentWalker name

* change doc

* move NoopQuerySegmentWalker and add document

* fix doc

Co-authored-by: yuanyi <yuanyi@freewheel.tv>

docs/development/extensions-contrib/moving-average-query.md

@@ -52,14 +52,14 @@ It runs the query in two main phases:
 ## Operations
 
 ### Installation
-Use [pull-deps](../../operations/pull-deps.md) tool shipped with Druid to install this [extension](../../development/extensions.md#community-extensions) on all Druid broker nodes.
+Use [pull-deps](../../operations/pull-deps.md) tool shipped with Druid to install this [extension](../../development/extensions.md#community-extensions) on all Druid broker and router nodes.
 
 ```bash
 java -classpath "<your_druid_dir>/lib/*" org.apache.druid.cli.Main tools pull-deps -c org.apache.druid.extensions.contrib:druid-moving-average-query:{VERSION}
 ```
 
 ### Enabling
-After installation, to enable this extension, just add `druid-moving-average-query` to `druid.extensions.loadList` in brokers' `runtime.properties` file and then restart broker nodes.
+After installation, to enable this extension, just add `druid-moving-average-query` to `druid.extensions.loadList` in broker and routers' `runtime.properties` file and then restart broker and router nodes.
 
 For example:
 
@@ -71,7 +71,6 @@ druid.extensions.loadList=["druid-moving-average-query"]
 There are currently no configuration properties specific to Moving Average.
 
 ## Limitations
-* movingAverage is not supported by Druid router(including the Web Console), all queries should be sent to broker nodes directly.
 * movingAverage is missing support for the following groupBy properties: `subtotalsSpec`, `virtualColumns`.
 * movingAverage is missing support for the following timeseries properties: `descending`.
 * movingAverage is missing support for [SQL-compatible null handling](https://github.com/apache/druid/issues/4349) (So setting druid.generic.useDefaultValueForNull in configuration will give an error).

server/src/main/java/org/apache/druid/server/NoopQuerySegmentWalker.java

@@ -0,0 +1,48 @@
+/*
+ * 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.server;
+
+import org.apache.druid.query.Query;
+import org.apache.druid.query.QueryRunner;
+import org.apache.druid.query.QuerySegmentWalker;
+import org.apache.druid.query.SegmentDescriptor;
+import org.joda.time.Interval;
+
+/**
+ * An empty implementation of {@link QuerySegmentWalker}.
+ *
+ * Some extentions need implementation of QuerySegmentWalker, but this class will not be used in
+ * router. Bind {@link NoopQuerySegmentWalker} in router to allow router load some extentions, which
+ * makes query can run through router.
+ */
+public class NoopQuerySegmentWalker implements QuerySegmentWalker
+{
+  @Override
+  public <T> QueryRunner<T> getQueryRunnerForIntervals(Query<T> query, Iterable<Interval> intervals)
+  {
+    return null;
+  }
+
+  @Override
+  public <T> QueryRunner<T> getQueryRunnerForSegments(Query<T> query, Iterable<SegmentDescriptor> specs)
+  {
+    return null;
+  }
+}

services/src/main/java/org/apache/druid/cli/CliRouter.java

@@ -38,8 +38,10 @@ import org.apache.druid.guice.RouterProcessingModule;
 import org.apache.druid.guice.annotations.Self;
 import org.apache.druid.guice.http.JettyHttpClientModule;
 import org.apache.druid.java.util.common.logger.Logger;
+import org.apache.druid.query.QuerySegmentWalker;
 import org.apache.druid.query.lookup.LookupSerdeModule;
 import org.apache.druid.server.AsyncQueryForwardingServlet;
+import org.apache.druid.server.NoopQuerySegmentWalker;
 import org.apache.druid.server.http.RouterResource;
 import org.apache.druid.server.http.SelfDiscoveryResource;
 import org.apache.druid.server.initialization.jetty.JettyServerInitializer;
@@ -91,6 +93,8 @@ public class CliRouter extends ServerRunnable
           JsonConfigProvider.bind(binder, "druid.router.avatica.balancer", AvaticaConnectionBalancer.class);
           JsonConfigProvider.bind(binder, "druid.router.managementProxy", ManagementProxyConfig.class);
 
+          binder.bind(QuerySegmentWalker.class).to(NoopQuerySegmentWalker.class).in(LazySingleton.class);
+
           binder.bind(CoordinatorRuleManager.class);
           LifecycleModule.register(binder, CoordinatorRuleManager.class);