[GitHub] [druid] jihoonson commented on a change in pull request #9407: query laning and load shedding

[GitBox <gi...@apache.org>]

jihoonson commented on a change in pull request #9407: query laning and load shedding
URL: https://github.com/apache/druid/pull/9407#discussion_r389125436
 
 

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 File path: server/src/main/java/org/apache/druid/server/QueryScheduler.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.server;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.HashMultimap;
+import com.google.common.collect.Multimaps;
+import com.google.common.collect.SetMultimap;
+import com.google.common.util.concurrent.ListenableFuture;
+import io.github.resilience4j.bulkhead.Bulkhead;
+import io.github.resilience4j.bulkhead.BulkheadConfig;
+import io.github.resilience4j.bulkhead.BulkheadRegistry;
+import it.unimi.dsi.fastutil.objects.Object2IntMap;
+import org.apache.druid.client.SegmentServerSelector;
+import org.apache.druid.java.util.common.concurrent.Execs;
+import org.apache.druid.java.util.common.guava.Sequence;
+import org.apache.druid.query.Query;
+import org.apache.druid.query.QueryContexts;
+import org.apache.druid.query.QueryPlus;
+import org.apache.druid.query.QueryWatcher;
+import org.apache.druid.server.initialization.ServerConfig;
+
+import java.time.Duration;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+
+/**
+ * QueryScheduler (potentially) assigns any {@link Query} that is to be executed to a 'query lane' using the
+ * {@link QueryLaningStrategy} that is defined in {@link QuerySchedulerConfig}.
+ *
+ * As a {@link QueryWatcher}, it also provides cancellation facilities.
+ *
+ * This class is shared by all requests on the Jetty HTTP theadpool and must be thread safe.
+ */
+public class QueryScheduler implements QueryWatcher
+{
+  static final String TOTAL = "default";
+  private final int totalCapacity;
+  private final QueryLaningStrategy laningStrategy;
+  private final BulkheadRegistry laneRegistry;
+  private final SetMultimap<String, ListenableFuture<?>> queryFutures;
+  private final SetMultimap<String, String> queryDatasources;
+
+  public QueryScheduler(int totalNumThreads, QueryLaningStrategy laningStrategy, ServerConfig serverConfig)
+  {
+    this.laningStrategy = laningStrategy;
+    this.queryFutures = Multimaps.synchronizedSetMultimap(HashMultimap.create());
+    this.queryDatasources = Multimaps.synchronizedSetMultimap(HashMultimap.create());
+    // if totalNumThreads is above 0 and less than druid.server.http.numThreads, enforce total limit
+    final boolean limitTotal;
+    if (totalNumThreads > 0 && totalNumThreads < serverConfig.getNumThreads()) {
+      limitTotal = true;
+      this.totalCapacity = totalNumThreads;
+    } else {
+      limitTotal = false;
+      this.totalCapacity = serverConfig.getNumThreads();
+    }
+    this.laneRegistry = BulkheadRegistry.of(getLaneConfigs(limitTotal));
+  }
+
+  @Override
+  public void registerQueryFuture(Query<?> query, ListenableFuture<?> future)
+  {
+    final String id = query.getId();
+    final Set<String> datasources = query.getDataSource().getTableNames();
+    queryFutures.put(id, future);
+    queryDatasources.putAll(id, datasources);
+    future.addListener(
+        () -> {
+          queryFutures.remove(id, future);
+          for (String datasource : datasources) {
+            queryDatasources.remove(id, datasource);
+          }
+        },
+        Execs.directExecutor()
+    );
+  }
+
+  /**
+   * Assign a query a lane (if not set)
+   */
+  public <T> Query<T> laneQuery(QueryPlus<T> queryPlus, Set<SegmentServerSelector> segments)
+  {
+    Query<T> query = queryPlus.getQuery();
+    // man wins over machine.. for now.
+    if (QueryContexts.getLane(query) != null) {
+      return query;
+    }
+    Optional<String> lane = laningStrategy.computeLane(queryPlus, segments);
+    return lane.map(query::withLane).orElse(query);
+  }
+
+  /**
+   * Run a query with the scheduler, attempting to acquire a semaphore from the total and lane specific query capacities
+   *
+   * Note that {@link #cancelQuery} should not interrupt the thread that calls run, in all current usages it only
+   * cancels any {@link ListenableFuture} created downstream. If this ever commonly changes, we should add
+   * synchronization between {@link #cancelQuery} and the acquisition of the {@link Bulkhead} to continue to ensure that
+   * anything acquired is also released.
+   *
+   * In the meantime, if a {@link ListenableFuture} is registered for the query that calls this method, it MUST handle
+   * this synchronization itself to ensure that no {@link Bulkhead} is acquired without releasing it.
+   */
+  public <T> Sequence<T> run(Query<?> query, Sequence<T> resultSequence)
+  {
+    List<Bulkhead> bulkheads = acquireLanes(query);
+    return resultSequence.withBaggage(() -> releaseLanes(bulkheads));
+  }
+
+  /**
+   * Forcibly cancel all futures that have been registered to a specific query id
+   */
+  public boolean cancelQuery(String id)
+  {
+    // if you re-use queryId and cancel queries... you are going to have a bad time
+    queryDatasources.removeAll(id);
+    Set<ListenableFuture<?>> futures = queryFutures.removeAll(id);
+    boolean success = true;
+    for (ListenableFuture<?> future : futures) {
+      success = success && future.cancel(true);
+    }
+    return success;
+  }
+
+  /**
+   * Get a {@link Set} of datasource names for a {@link Query} id, used by {@link QueryResource#cancelQuery} to
+   * authorize that a user may call {@link #cancelQuery} for the given id and datasources
+   */
+  public Set<String> getQueryDatasources(final String queryId)
+  {
+    return queryDatasources.get(queryId);
+  }
+
+  /**
+   * Get the maximum number of concurrent queries that {@link #run} can support
+   */
+  @VisibleForTesting
+  int getTotalAvailableCapacity()
+  {
+    return laneRegistry.getConfiguration(TOTAL)
+                       .map(config -> laneRegistry.bulkhead(TOTAL, config).getMetrics().getAvailableConcurrentCalls())
+                       .orElse(-1);
+  }
+
+  /**
+   * Get the maximum number of concurrent queries that {@link #run} can support for a given lane
+   */
+  @VisibleForTesting
+  int getLaneAvailableCapacity(String lane)
+  {
+    return laneRegistry.getConfiguration(lane)
+                       .map(config -> laneRegistry.bulkhead(lane, config).getMetrics().getAvailableConcurrentCalls())
+                       .orElse(-1);
+  }
+
+  /**
+   * Acquire a semaphore for both the 'total' and a lane, if any is associated with a query
+   */
+  @VisibleForTesting
+  List<Bulkhead> acquireLanes(Query<?> query)
+  {
+    final String lane = QueryContexts.getLane(query);
+    final Optional<BulkheadConfig> laneConfig = lane == null ? Optional.empty() : laneRegistry.getConfiguration(lane);
+    List<Bulkhead> hallPasses = new ArrayList<>(2);
+    final Optional<BulkheadConfig> totalConfig = laneRegistry.getConfiguration(TOTAL);
+    // if we have a lane, get it first
+    laneConfig.ifPresent(config -> {
+      Bulkhead laneLimiter = laneRegistry.bulkhead(lane, config);
+      if (!laneLimiter.tryAcquirePermission()) {
+        throw new QueryCapacityExceededException(lane);
+      }
+      hallPasses.add(laneLimiter);
+    });
+
+    // everyone needs to take one from the total lane; to ensure we don't acquire a lane and never release it, we want
+    // to check for total capacity exceeded and release the lane (if present) before throwing capacity exceeded
+    totalConfig.ifPresent(config -> {
+      Bulkhead totalLimiter = laneRegistry.bulkhead(TOTAL, config);
+      if (!totalLimiter.tryAcquirePermission()) {
+        releaseLanes(hallPasses);
+        throw new QueryCapacityExceededException();
+      }
+      hallPasses.add(totalLimiter);
+    });
+    return hallPasses;
+  }
+
+  /**
+   * Release all {@link Bulkhead} semaphores in the list
+   */
+  @VisibleForTesting
+  void releaseLanes(List<Bulkhead> bulkheads)
+  {
+    bulkheads.forEach(Bulkhead::releasePermission);
+  }
+
+  /**
+   * With a total thread count and {@link QueryLaningStrategy#getLaneLimits}, create a map of lane name to
+   * {@link BulkheadConfig} to be used to create the {@link #laneRegistry}. This accepts the configured value of
+   * numThreads rather than using {@link #totalCapacity} so that we only have a total {@link Bulkhead} if
+   * {@link QuerySchedulerConfig#getNumThreads()} is set
+   */
+  private Map<String, BulkheadConfig> getLaneConfigs(boolean hastotalLimit)
 
 Review comment:
   `hastotalLimit` -> `hasTotalLimit`

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