surekhasaharan commented on a change in pull request #6901: Introduce published segment cache in broker URL: https://github.com/apache/incubator-druid/pull/6901#discussion_r271479675
########## File path: sql/src/main/java/org/apache/druid/sql/calcite/schema/MetadataSegmentView.java ########## @@ -0,0 +1,255 @@ +/* + * 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.concurrent.LifecycleLock; +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.ISE; +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 javax.annotation.Nullable; +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; +import java.util.concurrent.atomic.AtomicBoolean; + +/** + * 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 EmittingLogger log = new EmittingLogger(MetadataSegmentView.class); + + private final DruidLeaderClient coordinatorDruidLeaderClient; + private final ObjectMapper jsonMapper; + private final BytesAccumulatingResponseHandler responseHandler; + private final BrokerSegmentWatcherConfig segmentWatcherConfig; + + private final boolean isCacheEnabled; + @Nullable + private final ConcurrentMap<DataSegment, DateTime> publishedSegments; + private final ScheduledExecutorService scheduledExec; + private final long pollPeriodInMS; + private final LifecycleLock lifecycleLock = new LifecycleLock(); + private final AtomicBoolean cachePopulated = new AtomicBoolean(false); + + @Inject + public MetadataSegmentView( + final @Coordinator DruidLeaderClient druidLeaderClient, + final ObjectMapper jsonMapper, + final BytesAccumulatingResponseHandler responseHandler, + final BrokerSegmentWatcherConfig segmentWatcherConfig, + final PlannerConfig plannerConfig + ) + { + Preconditions.checkNotNull(plannerConfig, "plannerConfig"); + this.coordinatorDruidLeaderClient = druidLeaderClient; + this.jsonMapper = jsonMapper; + this.responseHandler = responseHandler; + this.segmentWatcherConfig = segmentWatcherConfig; + this.isCacheEnabled = plannerConfig.isMetadataSegmentCacheEnable(); + this.pollPeriodInMS = plannerConfig.getMetadataSegmentPollPeriod(); + this.publishedSegments = isCacheEnabled ? new ConcurrentHashMap<>(1000) : null; + this.scheduledExec = Execs.scheduledSingleThreaded("MetadataSegmentView-Cache--%d"); + } + + @LifecycleStart + public void start() + { + if (!lifecycleLock.canStart()) { + throw new ISE("can't start."); + } + try { + if (isCacheEnabled) { + scheduledExec.schedule(new PollTask(), pollPeriodInMS, TimeUnit.MILLISECONDS); + } + lifecycleLock.started(); + log.info("MetadataSegmentView Started."); + } + finally { + lifecycleLock.exitStart(); + } + } + + @LifecycleStop + public void stop() + { + if (!lifecycleLock.canStop()) { + throw new ISE("can't stop."); + } + log.info("MetadataSegmentView is stopping."); + if (isCacheEnabled) { + scheduledExec.shutdown(); + } + log.info("MetadataSegmentView Stopped."); + } + + private void poll() + { + log.info("polling published segments from coordinator"); + final JsonParserIterator<DataSegment> metadataSegments = getMetadataSegments( + coordinatorDruidLeaderClient, + jsonMapper, + responseHandler, + segmentWatcherConfig.getWatchedDataSources() + ); + + final DateTime timestamp = DateTimes.nowUtc(); + while (metadataSegments.hasNext()) { + final DataSegment interned = DataSegmentInterner.intern(metadataSegments.next()); + // timestamp is used to filter deleted segments + publishedSegments.put(interned, timestamp); + } + // filter the segments from cache whose timestamp is not equal to latest timestamp stored, + // since the presence of a segment with an earlier timestamp indicates that + // "that" segment is not returned by coordinator in latest poll, so it's + // likely deleted and therefore we remove it from publishedSegments + // Since segments are not atomically replaced because it can cause high + // memory footprint due to large number of published segments, so + // we are incrementally removing deleted segments from the map + // This means publishedSegments will be eventually consistent with + // the segments in coordinator + publishedSegments.entrySet().removeIf(e -> e.getValue() != timestamp); + cachePopulated.set(true); + } + + public Iterator<DataSegment> getPublishedSegments() + { + if (isCacheEnabled) { + Preconditions.checkState( + lifecycleLock.awaitStarted(1, TimeUnit.MILLISECONDS) && cachePopulated.get(), Review comment: yeah, client would get `IllegalStateException` with the error message `hold on, still syncing published segments`, and they'll have to retry. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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