[GitHub] clintropolis commented on a change in pull request #6901: Introduce published segment cache in broker

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clintropolis commented on a change in pull request #6901: Introduce published segment cache in broker
URL: https://github.com/apache/incubator-druid/pull/6901#discussion_r252972457
 
 

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 File path: sql/src/main/java/org/apache/druid/sql/calcite/schema/MetadataSegmentView.java
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+/*
+ * 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.sql.calcite.schema;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.JavaType;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.common.base.Preconditions;
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.inject.Inject;
+import org.apache.druid.client.BrokerSegmentWatcherConfig;
+import org.apache.druid.client.DataSegmentInterner;
+import org.apache.druid.client.JsonParserIterator;
+import org.apache.druid.client.coordinator.Coordinator;
+import org.apache.druid.discovery.DruidLeaderClient;
+import org.apache.druid.guice.ManageLifecycle;
+import org.apache.druid.java.util.common.DateTimes;
+import org.apache.druid.java.util.common.StringUtils;
+import org.apache.druid.java.util.common.concurrent.Execs;
+import org.apache.druid.java.util.common.lifecycle.LifecycleStart;
+import org.apache.druid.java.util.common.lifecycle.LifecycleStop;
+import org.apache.druid.java.util.emitter.EmittingLogger;
+import org.apache.druid.java.util.http.client.Request;
+import org.apache.druid.server.coordinator.BytesAccumulatingResponseHandler;
+import org.apache.druid.sql.calcite.planner.PlannerConfig;
+import org.apache.druid.timeline.DataSegment;
+import org.jboss.netty.handler.codec.http.HttpMethod;
+import org.joda.time.DateTime;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Iterator;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * This class polls the coordinator in background to keep the latest published segments.
+ * Provides {@link #getPublishedSegments()} for others to get segments in metadata store.
+ */
+@ManageLifecycle
+public class MetadataSegmentView
+{
+
+  private static final long POLL_PERIOD_IN_MS = 60000;
+  private static final EmittingLogger log = new EmittingLogger(MetadataSegmentView.class);
+
+  private final DruidLeaderClient coordinatorDruidLeaderClient;
+  private final ObjectMapper jsonMapper;
+  private final BytesAccumulatingResponseHandler responseHandler;
+  private final BrokerSegmentWatcherConfig segmentWatcherConfig;
+
+  private final ConcurrentMap<DataSegment, DateTime> publishedSegments = new ConcurrentHashMap<>(1000);
+  private ScheduledExecutorService scheduledExec;
+  final PlannerConfig plannerConfig;
+
+  @Inject
+  public MetadataSegmentView(
+      final @Coordinator DruidLeaderClient druidLeaderClient,
+      final ObjectMapper jsonMapper,
+      final BytesAccumulatingResponseHandler responseHandler,
+      final BrokerSegmentWatcherConfig segmentWatcherConfig,
+      final PlannerConfig plannerConfig
+  )
+  {
+    this.plannerConfig = Preconditions.checkNotNull(plannerConfig, "plannerConfig");
+    this.coordinatorDruidLeaderClient = druidLeaderClient;
+    this.jsonMapper = jsonMapper;
+    this.responseHandler = responseHandler;
+    this.segmentWatcherConfig = segmentWatcherConfig;
+  }
+
+  @LifecycleStart
+  public void start()
+  {
+    if (plannerConfig.isMetadataSegmentCacheEnable()) {
+      scheduledExec = Execs.scheduledSingleThreaded("MetadataSegmentView-Cache--%d");
 
 Review comment:
   I think this needs some sort of synchronization and started check, maybe a `LifecycleLock` if it should start and stop with the service, or maybe just `lock` and `AtomicBoolean` if it can stop and start while service is running.

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